4_6032952067461482414

BS 8519:2020

BSI Standards Publication

Selection and installation of fire‑resistant power and control cable systems for life safety, fire‑fighting and other critical applications — Code of practice

BS 8519:2020

BRITISH STANDARD

Publishing and copyright information The BSI copyright notice displayed in this document indicates when the document was last issued. © The British Standards Institution 2020

Published by BSI Standards Limited 2020 ISBN 978 0 539 00951 4

ICS 13.220.20; 29.060.01

The following BSI references relate to the work on this document: Committee reference FSH/1 Drafts for comment 19/30377411 DC; 20/30413528 DC Amendments/corrigenda issued since publication Date

Text affected

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BS 8519:2020

Contents

Page

Foreword Introduction 1 Scope 2 Normative references 3 Terms and definitions 4 General 5 Fire survival times Table 1 — Recommended cable categories based on application 6 Power supplies 6.1 General Figure 1 — Example of dual supply — Mains with standby LV generation 6.2 Primary supply 6.3 Secondary supply Table 2 — Fuel storage capacity (based on BS EN 12101-10:2005) 7 Dual circuits/diverse routes 7.1 General 7.2 HV power supplies 7.3 LV power supplies 8 Fire-resisting building fabric enclosures 9 Automatic changeover devices 10 Motor control panels 11 Cable selection 12 Cable protective systems 12.1 General 12.2 Performance criteria 12.3 Installation criteria Figure 2 — Wall detail — cable enclosure 12.4 Cable transits, fire stopping, wall terminations and linear expansion 13 Effects of fire temperature on cable size 14 Use of circuit protective conductors (CPCs) 15 Cable installation practice 16 Cable support systems 17 Junction boxes and joints 17.1 Power cables 17.2 Control cables 18 Fire-resistant busbar systems 19 Areas of special fire risk 20 Life safety and fire-fighting applications 20.1 Sprinkler and wet riser pumps 20.2 Smoke control systems 20.3 Car park smoke control systems 20.4 Firefighters and evacuation lifts

Annex A (informative)  Selection and specification of UPS/battery inverter systems to serve as the secondary source of supply to life safety, fire-fighting and other critical systems Annex B (informative)  Typical high voltage (HV) circuit in a building

Annex C (informative)  Performance criteria for cable protective systems

iii 1 2 2 4 5 5 5 7 7 9 10 11 11 12 12 12 12 13 13 14 14 15 15 16 16 17 17 17 18 18 19 20 20 21 21 21 22 22 23 23 24

25 27 27

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Figure C.1 — Example of test arrangement for horizontal service ducts (fire exposure from outside), adapted from BS EN 1366-5:2003

Annex D (normative)  Testing of Category 3 cables of core sizes up to and including 4 mm2 crosssectional area Annex E (normative)  Determining the cross-sectional area of drop rods Figure E.1 — Typical thread detail identifying the major and minor diameters Figure E.2 — Elements of the cable support system Table E.1 — Maximum allowable stress of steel drop rods in fire conditions Table E.2 — Typical metric thread details (assumed to be coarse pitch) Annex F (informative)  Example voltage drop calculations for cables in a fire

28

29

30 31 32 32 33 33

Annex G (informative)  Fire-resistant cables under fire and fault conditions Table G.1 — Temperature correction factors for copper

36 36

Annex I (informative)  Guidance on calculating the mechanical loading on the drop rods Figure I.1 — Example of mechanical loading on the drop rods

37 38



40

Annex H (informative)  Cable protective systems to BS EN 1366‑11

Annex J (informative)  Variation from the recommendations of BS 8519:2020 Figure J.1 — Model completion certificate — Design — Declaration of conformity Bibliography

37

38 39

Summary of pages This document comprises a front cover, and inside front cover, pages i to iv, pages 1 to 40, an inside back cover and a back cover. ii © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED

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BS 8519:2020

Foreword Publishing information This British Standard is published by BSI Standards Limited, under licence from The British Standards Institution, and came into effect on 30 June 2020. It was prepared by Technical Committee FSH/1, Fire safety cables. A list of organizations represented on this committee can be obtained on request to the committee manager.

Supersession

This British Standard supersedes BS 8519:2010, which is withdrawn.

Information about this document

This is a full revision of BS 8519, and introduces the following principal changes: •

definitions added for:

○

average power output;

○

building fabric enclosure;

○ ○ ○ •

○

selectivity (discrimination); cable protective system;

electrical equipment enclosure; and other critical systems;

added recognition of other critical systems, other than life safety or fire-fighting applications;

•

added reference to fuel storage requirements in BS EN 12101‑10 (Clause 6);

•

added information on uninterruptable power supplies, UPS (Clause 6);

• • • • • • •

added recommendation to include fuel polishing equipment (Clause 6); added life safety generator recommendations;

added roof-mounted generator recommendations;

correction made to Table 1 sub-main power distribution minimum cable category;

Clause 7 generally updated for high voltage (HV) and low voltage (LV) cable routes;

Clause 9 revised to include further recommendations for the automatic transfer switch;

Clause 12 revised to include the recommendation for internal and external fire stopping to maintain the switchroom fire compartmentation and the need to cater for the thermal expansion of the cable protective enclosure;

•

added further detailed recommendations included in Clause 12 for the design and selection of the cable enclosure support systems;

•

Clause 18 fire-resistant busbar systems added;

• • •

Clause 17 junction boxes revised test protocol identified;

Clause 19 inverter text relocated to new subclause 20.2, smoke control systems;

Clause 20 multi-zoned smoke ventilation systems text relocated to new subclause 20.2, smoke control systems; © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED iii

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• new Clause 20 added providing recommendations for life safety and fire-fighting applications; and •

new informative Annex A on selection and specification of uninterruptable power supplies (UPS).

This publication can be withdrawn, revised, partially superseded or superseded. Information regarding the status of this publication can be found in the Standards Catalogue on the BSI website at bsigroup.com/standards, or by contacting the Customer Services team. Where websites and webpages have been cited, they are provided for ease of reference and are correct at the time of publication. The location of a webpage or website, or its contents, cannot be guaranteed.

Use of this document

As a code of practice, this British Standard takes the form of guidance and recommendations. It should not be quoted as if it were a specification and particular care should be taken to ensure that claims of compliance are not misleading.

Any user claiming compliance with this British Standard is expected to be able to justify any course of action that deviates from its recommendations.

Presentational conventions

The provisions of this standard are presented in roman (i.e. upright) type. Its recommendations are expressed in sentences in which the principal auxiliary verb is “should”.

Commentary, explanation and general informative material is presented in smaller italic type, and does not constitute a normative element. The word “should” is used to express recommendations of this standard. The word “may” is used in the text to express permissibility, e.g. as an alternative to the primary recommendation of the clause. The word “can” is used to express possibility, e.g. a consequence of an action or an event. Notes and commentaries are provided throughout the text of this standard. Notes give references and additional information that are important but do not form part of the recommendations. Commentaries give background information. Where words have alternative spellings, the preferred spelling of the Shorter Oxford English Dictionary is used (e.g. “organization” rather than “organisation”).

Contractual and legal considerations

This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations.

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BS 8519:2020

Introduction Buildings continue to develop in terms of increased size and height, and complexity of active fire protection. This has led to solutions being developed which require a high level of performance from the building services components, including the electrical supplies. This British Standard is primarily intended for designers, contractors, fire engineers, regulators and enforcers, including building control bodies, fire authorities and health and safety inspectors.

It is primarily concerned with cables which need to maintain their circuit integrity during a fire for life safety and fire-fighting purposes. However, the recommendations of this British Standard can also be used for cables which need to maintain their circuit integrity during a fire because the function they support is critical for business continuity, property protection or environmental protection. The presence of potential hazards, including fire, mechanical and water damage, are referred to throughout this British Standard.

This British Standard identifies electrical loads defined as life safety and fire-fighting. It identifies the factors to be accounted for by the engineer when selecting and specifying the performance requirements of the electrical distribution system needed to maintain circuit integrity under defined fire conditions for a specified period, referred to as the fire survival time. It makes reference to the recommendations of BS 9999 and BS 9991, with regard to the design and installation of the electrical distribution systems for life safety and fire-fighting equipment.

This British Standard also makes reference to three categories of circuits required to maintain their circuit integrity under defined fire conditions for varying fire survival times of 30 min, 60 min and 120 min. Appropriate cable tests are identified for each cable category derived from applicable British Standards assessing cable performance under conditions of fire as might be expected in an actual fire incident. This British Standard aims to ensure that the level of circuit fire integrity is not compromised by other components of the whole electrical distribution system, including cable glands, terminations, joints and cable support systems.

It also identifies the need for dual redundant electrical supplies run via diverse cable routes, installed within separate compartments, and the need to incorporate automatic changeover devices located within the same compartment as the life safety, fire-fighting or other critical equipment.

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BRITISH STANDARD

1 Scope This British Standard gives recommendations and guidance on the selection and installation of fire-resistant power and control cable systems which need to maintain their circuit integrity for life safety and fire-fighting. It also gives specific recommendations for electrical system design for such applications, and for fire survival times.

This British Standard is primarily intended for use in buildings which, due to their size, height, form or use, require the installation of life safety and fire-fighting systems, e.g. sprinkler pumps, wet riser pumps, smoke control systems, fire-fighting and evacuation lifts or other systems as required by the fire engineered strategy. It covers: •

the source of supply;

•

the appropriate location of the main intake rooms, HV switchrooms, LV switchrooms, transformer rooms, generator rooms, risers, fire life safety equipment plant rooms and fire‑fighting/evacuation lift motor rooms/shafts.

•

the distribution voltage [high voltage (HV) or low voltage (LV)]; and

The British Standard can also be used for systems which need to maintain their circuit integrity during a fire because the function they support is critical for business continuity, property protection or environmental protection reasons. This British Standard does not give recommendations for those installations covered in BS 5839‑1, BS 5839‑8, BS 5839‑9 and BS 5266‑1, but makes reference to these standards.



2 Normative references

The following documents are referred to in the text in such a way that some or all of their content constitutes provisions of this document.1) For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. BS 3643‑1, ISO metric screw threads — Part 1: Principles and basic data

BS 3643‑2, ISO metric screw threads — Part 2: Specification for selected limits of size2)

BS 5266‑1, Emergency lighting — Part 1: Code of practice for the emergency lighting of premises BS 5306‑1, Code of practice for fire extinguishing installations and equipment on premises — Part 1: Hose reels and foam inlets

BS 5839‑1, Fire detection and fire alarm systems for buildings — Part 1: Code of practice for design, installation, commissioning and maintenance of systems in non-domestic premises

BS 5839‑8, Fire detection and fire alarm systems for buildings — Part 8: Code of practice for the design, installation, commissioning and maintenance of voice alarm systems BS 5839‑9, Fire detection and alarm systems for buildings — Part 9: Code of practice for the design, installation, commissioning and maintenance of emergency voice communication systems

BS 7273‑4, Code of practice for the operation of fire protection measures — Part 4: Actuation of release mechanisms for doors

1) 2)

BS 7346 (all parts), Components for smoke and heat control systems

Documents that are referred to solely in an informative manner are listed in the Bibliography. This British Standard also gives an informative reference to BS 3643-2:2007.

2 © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED

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BS 7671, Requirements for Electrical Installations — IET Wiring Regulations3)

BS 7698‑12, ISO 8528-12, Reciprocating internal combustion engine driven alternating current generating sets — Part 12: Emergency power supply to safety devices

BS 7835, Electric cables — Armoured cables with thermosetting insulation for rated voltages from 3.8/6.6 kV to 19/33 kV having low emission of smoke and corrosive gases when affected by fire — Requirements and test methods BS 8434‑2, Methods of test for assessment of the fire integrity of electric cables — Part 2: Test for unprotected small cables for use in emergency circuits — BS EN 50200 with 930° flame and with water spray BS 8458, Fixed fire protection systems — Residential and domestic watermist systems — Code of practice for design and installation

BS 8489 (all parts), Fixed fire protection systems — Industrial and commercial watermist systems

BS 8491, Method for assessment of fire integrity of large diameter power cables for use as components for smoke and heat control systems and certain other active fire safety systems BS 8524 (both parts), Active fire curtain barrier assemblies

BS 8602, Method for assessment of fire integrity of cast resin busbar trunking systems for the safety critical power distribution to life safety and fire fighting systems

BS 8629, Code of practice for the design, installation, commissioning and maintenance of evacuation alert systems for use by fire and rescue services in buildings containing flats BS 9251, Fire sprinkler systems for domestic and residential occupancies — Code of practice BS 9990, Non-automatic fire-fighting systems in buildings — Code of practice

BS 9991, Fire safety in the design, management and use of residential buildings — Code of practice BS 9999:2017, Fire safety in the design, management and use of buildings — Code of practice

BS EN 81‑72, Safety rules for the construction and installation of lifts — Particular applications for passenger and goods passenger lifts — Part 72: Firefighters lifts BS EN 1363‑1, Fire resistance tests — Part 1: General requirements

BS EN 12094 (all parts), Fixed firefighting systems — Components for gas extinguishing systems BS EN 12101‑1, Smoke and heat control systems — Part 1: Specification for smoke barriers

BS EN 12101‑2, Smoke and heat control systems — Part 2: Natural smoke and heat exhaust ventilators BS EN 12101‑3, Smoke and heat control systems — Part 3: Specification for powered smoke and heat control ventilators (Fans) BS EN 12101‑6, Smoke and heat control systems — Part 6: Specification for pressure differential systems — Kits BS EN 12101‑8, Smoke and heat control systems — Part 8: Smoke control dampers BS EN 12101‑10, Smoke and heat control systems — Part 10: Power supplies4) BS EN 12416 (both parts), Fixed firefighting systems — Powder systems

BS EN 12845, Fixed firefighting systems — Automatic sprinkler systems — Design, installation and maintenance

3) 4)

This British Standard also gives an informative reference to BS 7671:2018+A1:2020. This British Standard also gives an informative reference to BS EN 12101-10:2005. © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED 3

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BS EN 13501‑2:2016, Fire classification of construction products and building elements — Part 2: Classification using data from fire resistance tests, excluding ventilation services BS EN 13565 (both parts), Fixed firefighting systems — Foam systems

BS EN 15004 (all parts), Fixed firefighting systems — Gas extinguishing systems

BS EN 50200:2015, Method of test for resistance to fire of unprotected small cables for use in emergency circuits

BS EN 50393, Test methods and requirements for accessories for use on distribution cables of rated voltage 0,6/1,0 (1,2) kV BS EN 60947 (all parts), Low-voltage switchgear and controlgear

DD CEN/TS 14816, Fixed firefighting systems – Water spray systems – Design, installation and maintenance



3 Terms and definitions For the purposes of this British Standard, the following terms and definitions apply.

3.1 average power output

ratio of the average load demand to the rated generator power

3.2 building fabric enclosure

elements of a building that in combination offer a specified level of fire resistance and water ingress protection to protect the life safety, fire-fighting and other critical equipment NOTE











These elements can comprise walls, floors, doors, etc.

3.3 cable protective system factory-manufactured insulated enclosure providing thermal, mechanical and water protection to the life safety, fire-fighting and other critical system cables installed within the enclosure to maintain their circuit integrity with a fire condition external to the enclosure

3.4 electrical equipment enclosure

control panel or switchgear enclosure accommodating control, indication and protective devices serving the life safety, fire-fighting and other critical system equipment

3.5 fire-resistant cable

cable able to maintain circuit integrity for a stated fire survival time and under conditions as defined in a standard test

3.6 other critical systems

systems, other than life safety and fire-fighting, that by virtue of their importance to business resilience, property protection or protection of the environment or safety, are specified as required to remain operable during a fire for a predefined period

3.7 selectivity (discrimination)

ability of a protective device to operate in preference to another protective device in series

3.8 substation

switch room of an electricity transmission and distribution system where voltage is transformed from high to low voltage or the reverse using transformers 4 © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED

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BS 8519:2020

4 General The electrical system should be designed, installed and verified by a skilled person suitably competent to comply with BS 7671 and to install switchgear and controlgear conforming to BS EN 60947.

The type of electrical distribution system selected during the design phase should be derived from a detailed process of consultation with the relevant authorities having jurisdiction over the project in question, taking account of the overall fire strategy. The design should be agreed at the earliest stage. NOTE Specifically with reference to other critical systems, the appropriate levels of fire survival time are agreed in consultation between all interested parties.



5 Fire survival times The minimum fire survival time of the power and control (cable) circuits should be categorized as follows: a) circuit category 1: 30 min fire survival time;

b) circuit category 2: 60 min fire survival time; or c) circuit category 3: 120 min fire survival time.

The recommended cable categories shown in Table 1 should be used for specific life safety and fire‑fighting applications.

NOTE The fire survival time of power and control (cable) circuits to life safety, fire-fighting and other critical systems within buildings is dependent on the fire survival time of the building fabric and the cable/busbar installation. In fire engineered buildings designed to BS 7974, the fire survival time of the building fabric might vary according to the fire strategy, as part of a fire engineered solution.

Table 1 — Recommended cable categories based on application System

Related standards A)

Application

Minimum cable

Fire alarms

BS 5839‑1

Standard

(1) B)

 

BS 8629

Enhanced

(3) B)

category  

Evacuation systems Communications        

Emergency lighting    

BS 5839‑1 BS 8629

BS 5839‑9 BS 5839‑9 −

BS 5839‑8 BS 5839‑8 BS 5266‑1 BS 5266‑1 BS 5266‑1

Sub-main power distribution − (see Figure 1)  

Smoke and heat control: Fire‑fighting

−

BS 7346‑7, BS 7346‑8

Enhanced Standard

Disabled evacuation alarms (refuges)

Emergency voice communication systems

Closed-circuit television (CCTV) Voice alarm systems – standard

Voice alarm systems – enhanced Emergency escape lighting Escape route lighting

Central battery and distribution Fire-fighting applications

Means of escape applications Car park smoke control

(3) B) (1) B) (3) B) (3) B) 2

(1) B) (3) B) (2) B) (2) B) (2) B) 3

1 or 2 3 C)

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Table 1 (continued) System

Related standards A)

Application

Minimum cable category

                 

−

BS EN 12101‑8 BS EN 12101‑1

BS 8524 (both parts) BS EN 12101‑2 BS EN 12101‑3 BS EN 12101‑1 BS EN 12101‑3 −

 

−

Means of escape

BS 7346‑7

                         

Fire-fighting shafts      

BS EN 12101‑6 −

BS EN 12101‑8 BS EN 12101‑1 −

BS EN 12101‑2 BS EN 12101‑3 BS EN 12101‑1 BS EN 12101‑3 − −

BS EN 12101‑6 BS 7273‑4

BS EN 12101‑6 − −

BS 9999

Wiring in other areas of special fire risk

Smoke control dampers – supply and control

Smoke barriers – supply and control

3 C) 3 3

Fire barriers – supply and control 3 Natural smoke and heat exhaust

2

Powered SHEVS – supply and

2 or 3 D)

ventilation systems (SHEVS) – supply and control control

Smoke curtains – supply and control

Smoke fans

Smoke shafts – controlled motorized fire and smoke dampers (MFSDs)

3 3 2

Powered smoke shafts and

3

Car park smoke clearance

2

controlled MFSDs Pressurization

Wiring in other areas of special fire risk

Smoke control dampers – supply and control

Smoke barriers – supply and control

3

3 C) 2 2

Fire barriers – supply and control 2 Natural SHEVS – supply and control

Powered SHEVS – supply and control

Smoke curtains – supply and control

Smoke fans

Smoke shafts – controlled MFSDs Powered smoke shafts and controlled MFSDs Pressurization

Powered sliding doors Pressurization

Chimneys – controlled (MFSD) dampers

1 or 2 F) 2 2 3 2 2 2 2 3 3

Powered chimneys and controlled 3 MFSDs

Fire-fighting shaft normal lighting 3 G)

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Table 1 (continued) System

Related standards A)

Application

Minimum cable category

 

BS 9999

Fire-fighting shaft system

3 G)

 

BS EN 81‑72

Fire-fighting – Communications

(3) B)

Lifts    

Fire suppression      

BS 9999 BS 9999 −

BS 8489 (all parts) parts)

BS EN 12845

 

BS 9251

 

BS EN 13565 (both parts)

 

BS 5306‑1

   

Fire mains  

Evacuation – Lift supplies

Evacuation – Communications

BS EN 15004 (all parts) Gaseous extinguishing systems BS EN 12416 (both

 

Fire-fighting – Lift supplies

BS EN 12094 (all parts) Gaseous extinguishing systems BS 8458

 

monitoring

DD CEN/TS 14816 −

BS 9990 −

Water mist

Water mist – residential Powder systems

Sprinkler systems

Sprinkler systems – residential Automatic foam systems Hose reel systems

Water spray systems

Suppression system monitoring Wet riser pumps

Valve and equipment monitoring

NOTE Further guidance on power supplies is given in BS EN 12101‑10.

3 2

(2) B) 2 2 3 2 2 3 2 2 3 3 2 3 3

Refer to these standards for further information on the relevant system or application.

A) B)

The categories given in parentheses are approximately equivalent to the cable performance recommendations given in the related standards, and are included here for information. The actual cable performance recommendations for these applications are given in the related standards.

See Clause 19 for information on areas of special fire risk.

C)

Use minimum Category 2 or 3 depending on the type of system (60 min or 120 min).

D) E)

Use minimum Category 2 for automatic system activation, or Category 3 for firefighters’ manual override.

Use minimum Category 1 for automatic system activation, or Category 2 for firefighters’ manual override.

F)

Use minimum Category 3 control cables and provide mechanical protection where necessary.

G)



6 Power supplies 6.1 General Where electrical services in the building are essential to maintain the operation of the life safety, fire‑fighting or other critical systems, a secondary power supply should be provided independent of the primary supply, typically an automatically started standby generator (see Figure 1).

The secondary power supply should be of sufficient capacity and resilience to maintain the life safety, fire-fighting and other critical systems in operation for at least the fire survival time identified in Clause 5 for the appropriate systems and be capable of operating safely in fire conditions for the appropriate period of time. © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED 7

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The components of the primary supply should be separated from the components of the secondary supply so that a failure of a cable or equipment in either supply does not affect the other supply. The secondary supply should preferably be an automatic starting standby generator.

NOTE 1 The designer may incorporate alternatives, provided that the integrity and independent nature of supply can be guaranteed. NOTE 2 If the secondary supply is an alternative HV supply from a utility primary network, refer to BS 7671:2018, regulation 560.6.5: “Separate independent feeders from a distributors network shall not serve as electrical sources for safety services unless assurance can be obtained that the two supplies are unlikely to fail concurrently”.

Dual independent incoming low voltage utility supplies should not be considered to be sufficiently independent and resilient to be suitable for dual independent electrical supplies to life safety and fire-fighting equipment unless designed in accordance with the recommendations for primary and secondary power supplies in BS 9999:2017, 37.2.3.3.

Where the installation of UPS equipment/battery inverter systems are proposed, their performance, rating and suitability for the intended purpose should be evaluated by the specifier/designer. The advice of the specialist manufacturer should be sought to ensure the UPS equipment provides the appropriate level of resilience, capacity and endurance as that offered by a life safety generator serving as the secondary means of supply.

NOTE 3 Refer to Annex A for technical guidance on the selection and specification of UPS/battery inverter systems intended to provide the secondary source of supply to life safety, fire-fighting and other critical systems.

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Figure 1 — Example of dual supply — Mains with standby LV generation

NOTE

ATS stands for automatic transfer switch.

NOTE 4 Figure 1 is an example of the typical distribution arrangement recommended by this British Standard to feed life safety and fire-fighting equipment. It does not preclude alternative arrangements that ensure fire integrity and availability of both the primary and secondary supplies. NOTE 5 HV switchgear, LV switchgear and transformers may be installed within the same 120 min fire-resistant building fabric enclosure. Generators and their associated distribution equipment may also be installed within the same 120 min fire-resistant building fabric enclosure, but separate from the primary supply equipment, provided the equipment is suitable for the environment in which it is to be installed and system resilience is maintained.

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NOTE 6 In Figure 1, 120 min fire resistance for the building fabric enclosure is recommended even for life safety or other critical systems requiring 30 min or 60 min fire survival time. This is because fire test standards for cables and structural elements are fundamentally different. If justified by a fire engineering analysis in accordance with BS 7974, an alternative building fabric fire-resisting period may be selected instead of 120 min.

Each connection at the power supply source should be via an isolating protective device reserved solely for the individual items of life safety and fire-fighting equipment and independent of any other main or sub-main circuit. Such isolating protective devices should be clearly labelled and identified as to their purpose and should be secured against unauthorized operation. The primary and secondary power sources, electrical distribution boards, cables and control equipment supplying power to the life safety and fire-fighting equipment (see Figure 1) should be protected against fire and water damage for a period of at least the fire survival time identified in Clause 5 for the appropriate systems.

NOTE 7 Typically, the transformers and main LV switchgear enclosures are specified as a minimum of IP31 in accordance with BS EN 60529:1992+A2:2013. Therefore it is for the designer to identify the appropriate location and type of construction for the switchroom enclosures to minimize the risk of water ingress.

The fire-resisting building fabric enclosure for the equipment should have a minimum fire resistance of 120 min.

The electrical distribution system supplying the life safety and fire-fighting equipment should be designed in such a way as to ensure that power is available at all times. To achieve this, dual supplies should be provided to each of the critical items of equipment; the supplies being via an automatic changeover device installed within the same fire compartment formed by the switchroom or plant room enclosure, minimizing the cable length between the ATS and the critical equipment. NOTE 8 The primary supply is generally derived from the mains or utility supply, whilst the secondary supply is derived from a standby generator.



6.2 Primary supply The incoming utility supply cables should, where practicable, enter directly the HV/LV switchrooms and not pass through the building. Where HV supply cables need to be routed through the building, the HV cable routes should be fire protected for 120 min, which can be achieved in one of the following ways: a) enclosed for their entire length by a cable protective system comprising passive fire protection material (see Clause 12); b) routed within a dedicated shaft or void of appropriate fire rating; or c) installed within a concrete trench with concrete cover.

Account should be taken of the reduction in the current rating of cables which occurs when they are enclosed. If necessary, the cable manufacturer should be consulted. NOTE 1 For cables installed within a concrete trench, derating factors are published in BS 7671.

NOTE 2 For cables installed within an enclosure of passive fire protection material, no ratings have been published but a derating factor of 50% is generally considered appropriate and may be used unless the manufacturer of the protective system advises a different derating factor for their particular system. NOTE 3 An example of a cable size calculation is given in Annex B.

Where two independent utility supplies are to be installed, the two supply cable routes should be adequately separated from each other to avoid a single fault affecting both supplies.

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BS 8519:2020

6.3 Secondary supply The standby generator should start automatically and be adequately sized to maintain in operation the maximum design load and be able to support the worst-case transient load and fault conditions. The fuel storage capacity should be not less than the minimum shown in Table 2.

Table 2 — Fuel storage capacity (based on BS EN 12101-10:2005) Criteria

Minimum fuel storage at full load

Generator set dedicated to the building life safety/ fire-fighting systems:

4h

a) only starts in case of a fire signal; and

b) provides fault indication to a permanently manned control room

Generator operates whenever the primary power source fails and provides fault indication to a permanently manned control room Otherwise

8h

72 h A)

For applications other than life safety and fire-fighting, the time period is as determined by the fire engineered strategy.

A)

The designer should provide fuel polishing equipment, where recommended by the generator specialist, to maintain the quality of the fuel due to the likelihood of the fuel remaining in the storage tank for an extended period. NOTE 1 Increased biofuel content of the diesel increases the risk of the engine performance being adversely affected by the degradation of the fuel quality over time.

The generator-starting electrical supply should also be independent of the primary source of supply (i.e. it should incorporate a battery automatic starting system). The rating of the generator should be selected in accordance with BS 7698‑12, ISO 8528‑12 as either prime or standby rated; for the standby set the variable average power output should not exceed 70%.

The electrical output in terms of voltage and frequency stability should be classified as G2 or better in order to provide the quality of supply equivalent to the primary mains supply. The designer should identify the effects of transient voltage conditions under starting and fault events. NOTE 2 For generator performance, refer to IEC 60364‑5‑56 and BS ISO 8528‑5.

The standby generator should be capable of providing the supply to the critical life safety and fire-fighting load within 15 s of the failure of the primary supply in accordance with BS 9999 and BS EN 12845.

Visual indication should be provided at the main fire alarm panel of the fire control room, giving the operational state of the standby generator, including mains healthy, generator running and generator fault. A voltmeter and ammeter should also be provided to indicate the total load on the generator, in accordance with BS EN 12101‑10. The standby generator should be installed within a 120 min fire-resisting building fabric enclosure rated 120 min EI in accordance with BS EN 13501‑2:2016 (except for doors which should be 120 min ESa) unless it is installed outside of the building, either at ground floor or roof level. The roof slab supporting the equipment should provide 120 min fire separation (REI in accordance with BS EN 13501‑2:2016). Where both the primary and secondary supplies are located on the ground floor or roof level, the designer should ensure that they are suitably protected such that the risk of a fire affecting both supplies is minimized as far as practicable. This should be achieved by enclosing each within a 120 min fire-resisting enclosure (REI, EI or ESa in accordance with BS EN 13501‑2:2016) or by

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separation if it can be shown by a fire safety engineering analysis by a suitably qualified fire safety engineer that fire or smoke will not spread from one to the other. A 120 min fire compartmentation (EI or ESa as appropriate) should also be provided to physically separate the generator from any adjacent fire risks either at ground floor or roof level. NOTE 3 If justified by a fire engineering analysis in accordance with BS 7974, an alternative building fabric fire‑resisting period may be selected instead of 120 min.

A local fuel service tank should be provided within the generator building fabric enclosure large enough for at least 120 min of operation at rated power, including the appropriate bunding to protect against the risk of a fuel leak.





Whichever secondary power source is provided, the distribution should be organized such that the secondary supply remains live when the remainder of the supplies in the building are isolated in an emergency.

7 Dual circuits/diverse routes 7.1 General

Both the primary and the secondary supplies should be protected against fire and water damage and be separated from each other throughout the installation, by adopting diverse cable routes.

7.2 HV power supplies

Where HV supply cables from the electrical utility intake rooms need to be routed through the building to HV switchrooms and transformer rooms, both the primary and secondary supply cables should be protected against the risk of damage by exposure to fire and water.

Standard HV cables conforming to BS 7835 should be installed within cable protective systems, capable of giving thermal protection and limiting the cable operating temperature, with a fire condition external to the enclosure, to less than the cable’s maximum emergency 120 min operating temperature of 250 °C, i.e. maximum temperature rise above ambient of 180 °C; assuming an initial conductor temperature of 70 °C under load conditions. NOTE



For further guidance, see Annex C.

7.3 LV power supplies When designing diverse cable routes, any fire risks located within the area of the cable route should be identified. Where the diverse routes come together in the same area (external to the fire-resisting and water-protected building fabric enclosure housing the life safety and fire-fighting equipment), they should be separated by fire compartmentation with a fire resistance period of at least the fire survival time in Clause 5 for the appropriate system. In the case of two low-voltage cables (i.e. 400 V 3-phase), the cables should be selected for the appropriate fire survival time (see Clause 11 for cable selection and Clause 5 for the fire survival times).

The life safety, fire-fighting and other critical system cables should be installed on a dedicated cable support system, independent of other cable support systems and designed to maintain its circuit integrity when exposed to fire conditions for a period of at least the survival time in Clause 5 for the appropriate system that it supports.

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8 Fire-resisting building fabric enclosures Switchrooms, substations and plant rooms containing any of the following equipment feeding the life safety, fire-fighting and other critical system equipment should be separated from other non‑fire‑fighting building services and the rest of the building by a fire-resisting enclosure classified REI or EI 120 in accordance with BS EN 13501‑2:2016, with the exception of any doorsets which should be classified ESa 120 unless otherwise stated in the specific related standard: •

high-voltage switchgear;

•

low-voltage switchgear;

•

motor control panels;

• transformers; • • •

distribution boards;

smoke control/clearance plant; pressurization plant;

•

communication equipment;

•

any other equipment associated with life safety and fire-fighting systems.

•

automatic changeover devices, with their associated switchgear; and

NOTE If justified by a fire engineering analysis in accordance with BS 7974, an alternative building fabric fire‑resisting period may be selected instead of 120 min.



9 Automatic changeover devices The primary and secondary power supply cables should be terminated in a changeover device (automatic transfer switch) located within:

a) a plant room(s) housing the life safety, fire-fighting or other critical system equipment; or

b) in the case of a firefighters lift, within the fire-fighting shaft outside the lift well or within a fire protected building fabric enclosure directly adjacent to the fire-fighting shaft.

The changeover device should automatically effect the transition from the primary to the secondary power supply in the event of the loss of the primary supply to the life safety, fire-fighting or other critical system plant.

Changeover devices should conform to BS EN 60947‑6‑1, and should be based on switch technology (PC classification), rather than circuit breakers or contactors. The automatic transfer switch (ATS) should be a single component with integrated controller from the same manufacturer.

Where occupation of the building is conditional upon the availability of the life safety and fire-fighting equipment, a single or dual bypass arrangement should be provided to enable the changeover device to be maintained without loss of service from the critical plant. NOTE 1 Where a single bypass is considered necessary, this comprises a single bypass on the primary supply.

The designer should carry out a design risk assessment for the specific application to identify the impact of the loss of service, for example, during planned maintenance. It should identify whether there are alternative management activities that could be put in place that would overcome the need for the bypass. It should also be strictly in accordance with the specific maintenance requirements for the switching device, recommended by the manufacturer.

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The ATS should be selected and specified by the designer with a utilization category of either AC33A or AC33B (i.e. motor loads or mixed loads including motors, resistive loads and 30% incandescent lamp loads as recommended by BS EN 60947‑6‑1).

The ATS device should meet the PC classification conforming to BS EN 60947‑6‑1 in terms of its short circuit capability, being capable of making and withstanding, but not breaking, short-circuit currents. The appropriate protective devices should be provided upstream of the ATS for both the primary and secondary supplies for protection coordination.

The ATS should give a clear indication of the “Normal”, “Off” (where provided) and “Alternative” switch positions. The operating mechanism should be interlocked to prevent simultaneous connection to both primary and secondary supplies. Remote indication should also be provided of the ATS status to the main fire alarm panel or the fire control room. The ATS should monitor the voltage and frequency of both the primary and secondary supplies, transferring from primary to secondary automatically in the event of primary mains supply failure. The status/condition of the primary and secondary supplies should also be monitored remotely. NOTE 2 When power to the primary supply has been restored, return to the primary supply can be manual or automatic.



Category 3 fire-resistant control cables should be installed from each ATS to the generator to provide the start signal and status indication in the event of the loss of supply to an individual ATS. Unprotected fire-resistant control cables should be further protected in areas where mechanical damage is likely (e.g. armoured cable or cable tray with lid).

10 Motor control panels

Motor control panels serving the appropriate life safety, fire-fighting or other critical circuits should be protected to a minimum of IP54 classification where wet services are present. NOTE 1 IP54 classification is defined in BS EN 60529:1992+A2:2013.

If a fire control room is provided, it should contain monitoring facilities to show, as far as is reasonably practicable, that power is available to the life safety, fire-fighting and other critical equipment.

NOTE 2 The regulatory authorities usually require exact details of all switchboard, automatic transfer switches and standby generator enclosures (including oil storage) associated with life safety systems to be submitted for approval, including location, ratings, operation, fire rating proposals and protection afforded.



11 Cable selection The cables selected for life safety, fire-fighting or other critical systems should be either:

a) high voltage: standard HV cables, having supplementary protection as described in 7.2; or NOTE 1 These cables conform to BS 7835.

b) low voltage: fire-resistant cables meeting the minimum fire survival time categories for the appropriate application as shown in Table 1. NOTE 2 These cables conform to BS 7629‑1, BS 7846 or BS EN 60702‑1.

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NOTE 3 The categories given in Table 1 are defined as follows, based on the fire survival time required of the cable (i.e. 30 min, 60 min or 120 min).

1) Category 1: means of escape (30 min fire survival time); category 1 cables should be one of the following: • •

power cables meeting the 30 min survival time when tested in accordance with BS 8491; or control cables having a fire survival time of 30 min when tested in accordance with BS EN 50200:2015, and the 30 min survival time when tested in accordance with BS EN 50200:2015, Annex E (core sizes up to and including 4 mm2 cross-sectional area), excluding 3-phase power circuits.

2) Category 2: means of escape (60 min fire survival time); category 2 cables should be one of the following: • •

power cables meeting the 60 min survival time when tested in accordance with BS 8491; or control cables having a fire survival time of 60 min when tested in accordance with BS EN 50200:2015, and the 120 min survival time when tested in accordance with BS 8434‑2 (core sizes up to and including 4 mm2 cross-sectional area), excluding 3-phase power circuits.

3) Category 3: fire-fighting (120 min fire survival time); category 3 cables should be one of the following: • •

power cables meeting the 120 min survival time when tested in accordance with BS 8491; or

control cables having a fire survival time of 120 min when tested in accordance with BS EN 50200:2015, and the 120 min survival time when tested in accordance with BS 8434‑2 (core sizes up to and including 4 mm2 cross-sectional area) and Annex D (core sizes up to and including 4 mm2 cross-sectional area), excluding 3-phase power circuits.

When a Category 3 control cable is used as a single-phase small power cable, then a mechanically‑protected (e.g. armoured) cable should be used or additional mechanical protection should be provided.

NOTE 4 Power cables of overall diameter less than 20 mm may be used if they can be demonstrated to give the same level of fire resistance as in BS 8491, which identifies test criteria for cables over 20 mm in overall diameter. NOTE 5 An application list is provided in the third column of Table 1, allowing the appropriate cable category for each application to be determined by the system designer/installer. Where a relevant application document exists, it is noted in the second column for reference.



12 Cable protective systems COMMENTARY ON CLAUSE 12 Cable protective systems, either riser ducts and shafts, or proprietary supplementary cable protective systems may be used as a means of protecting non-fire-resistant high-voltage cables (see Clause 6).



12.1 General The cable protective systems should be four-sided, fully enclosing the cables to be protected. Two and three-sided systems installed against the building structure should not be used, as the interface between the two represents a significant risk to the fire integrity of the cable protective system because it is impossible to assess the quality and fire performance upon completion of the site installation. The cable protective systems should provide the required thermal, mechanical and water protection for a minimum fire survival time of 120 min. The fire-resistant cable protective system © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED 15

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should be a factory-built assembly, designed to minimize reliance on the quality and workmanship on site, to ensure quality control and fire integrity performance is maintained throughout the installation.

The fixings or suspension system for the cable protective system should be capable of supporting the load of the cable protective system and its contents so that the circuit integrity of the cables therein is not compromised for a minimum fire survival time of 120 min.

The cable protective system should not contain any other services, other than the cable(s) to be protected and the primary and secondary supply cables should not be installed within the same cable protective system.



Warning labels should be applied to and visible on each section of a cable protective system stating that the installation should not be dismantled or altered in any way or used to support any other service. The label should identify life safety services and HV cables contained within the relevant section of the cable protective system.

12.2 Performance criteria

The protective system should meet the performance requirement for 120 min. NOTE



For further information on the performance of the cable protective system, see Annex C.

12.3 Installation criteria Where the fire-resistant cable protective system penetrates the fire compartmentation of switchrooms, it should not only provide thermal protection to the enclosed cables, but also maintain the fire integrity of the fire compartmentation, both externally and internally to the cable protective system, at both ends, to reduce the risk of fire spread from one room to another via the cable protective system. The fire resistance performance of the internal and external fire barriers should be equivalent to the BS EN 13501‑2 classification of the element (wall, floor, ceiling, etc.) through which the cable protective system passes. Where the cable protective systems are to be installed from the utility intake substation containing liquid filled transformers, blast protection should also be provided where necessary.

The services penetration into the intake room should maintain the fire integrity of the room enclosure. Suitably-rated cable transits, typically 10 kN/m2 (10 kPa), should be installed in the utility intake room wall, providing the required fire and blast rating (see Figure 2).

The HV cable protective system should be terminated against the inner face of the electrical intake room wall, ensuring the thermal protection to the HV cable is maintained. The other end of the cable protection system should penetrate the compartmentation with the appropriate internal and external fire stopping, which can accommodate thermal expansion of the cable protective system. Cable support systems should take into account the weight of the cable protective enclosure, the cables within it and the performance of the supporting structure with expansion limited to 40 mm to minimize the stress on the penetration sealing system. When designing support components, the installer should be suitably trained and utilize the correct anchor/fastenings into the supporting structure, fixed in accordance with the manufacturer’s instructions.

The fixings should be suitable for the density/grade and type of substrate into which they are installed. Anchors/fasteners should be verified as being fit for purpose in the particular substrate in question, and the performance under fire conditions should be confirmed by supporting evidence of fire resistance performance. 16 © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED

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If mild steel drop rods are to form the suspension element of the support system, their cross-sectional area should be determined in accordance with Annex E.

Figure 2 — Wall detail — cable enclosure

In selecting mild steel threaded rod support mechanisms, the maximum stress for fire exposure times of 120 min should not exceed 6 N/mm2 within vertically-orientated support components. NOTE Proprietary alternatives to threaded rod suspensions may be used if it can be verified that these have been furnace tested in accordance with the BS EN 1363‑1 fire curve and shown to be able to withstand the proposed imposed loads for the fire survival time of 120 min.





The physical integrity of the cable protective enclosures should not be compromised by any non-fire rated services that might fail prematurely. The enclosures should be installed above or beyond the influence of any non-fire rated services.

12.4 Cable transits, fire stopping, wall terminations and linear expansion

Although correctly tested systems prevent fire break-in (as proven by fire outside or type A fire test exposure), fire stopping internally within the cable protective system should be provided. The expansion of cable protective systems under fire conditions and their reaction with the building structure should also form part of the design process to ensure that the protection to both the enclosed cables and the fire compartmentation is maintained.

13 Effects of fire temperature on cable size COMMENTARY ON CLAUSE 13

When a cable is involved in a fire, the conductor temperature rises above the maximum conductor temperature upon which tabulated current rating and voltage drop data are based. This has implications for voltage drop, current rating and the effects of fault currents.

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A number of factors can affect any necessary “de-rating” such as length of cable exposed in the fire, actual temperature of the cable in the fire, heat flux exposure of the cable to the fire, and actual current to be carried under fire conditions. Assumptions therefore have to be made in assessing the effects on cable sizing. Cables for circuits covered by this standard are most likely to be sized on the basis of voltage drop, although other factors could apply in certain applications. The voltage drop at typical fire temperatures is higher than at normal maximum operating temperature and this can be significant for certain types of load. Assuming a worst case of the total length of cable run in the fire, it would be necessary to increase the conductor size by approximately two sizes. It is possible to calculate the voltage drop for cables involved in a fire by assuming the cable temperature in a fire and the cable length affected. Examples of the calculation are given in Annex F. Information on the effects of fault currents on cables operating under fire conditions is given in Annex G. The process of cable sizing and selection for fire-resistant cable should take account of the effects on the cable performance from the increased operating temperature above its normal maximum ambient temperature likely to be experienced under fire conditions. NOTE

In practice, for this standard this temperature is taken as 842 °C in accordance with BS 8491.

Where provided, any guidance given in the applicable Wiring Regulations (BS 7671) or specific advice from the cable manufacturer should be taken into account in selecting the appropriate cable for the load being fed under the fire conditions specified.





In the absence of any such guidance and where specific detailed calculations are not possible, there should be an increase of the conductor size by two sizes (compared with that selected for normal operation) in order to alleviate the effect of increased temperature on voltage drop and current rating.

14 Use of circuit protective conductors (CPCs)

Cable sizes should be selected to ensure that the earth fault loop impedance of the appropriate circuit from source to final load can be accommodated, and, in particular, the impedance contribution of the cable being sized. The total earth fault impedance should be sufficiently low to ensure that the prospective earth fault current is high enough to trip the circuit protective device in the required time.

15 Cable installation practice

When installing cables that are required to maintain circuit integrity under fire conditions, the resistance to fire of the cable fixings, cable support system and any joints should be at least equivalent to the survival time required for the cable. Cables should be installed in accordance with the following recommendations.

a) Where fire-resistant cables have by their method of construction adequate mechanical protection (e.g. cables conforming to BS 7629‑1, BS 7846 and BS EN 60702‑1), they should either be fixed directly to the building structure, or be installed such that they are enclosed in or carried upon cable management or support systems [see 15b)]. If the cables are fixed directly to the building, the fixings should provide adequate support in the presence of the potential hazards. NOTE

More information is given in the Introduction of this British Standard.

b) Where fire-resistant cables require additional mechanical protection, they should be enclosed in or carried upon cable management or support systems. Such systems should provide adequate 18 © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED

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support and maintain necessary mechanical protection in the presence of the potential hazards. The supports should be sized to cater for the reduction in the strength of steel when exposed to the effects of fire or it should be determined that the supports can withstand the proposed loads for the time duration required by the BS EN 1363‑1 fire curve.

c) Cable management or support systems that are not used as a primary means of support or to provide necessary mechanical protection should not compromise the defined performance of the cables in the presence of the potential hazards. d) Any glands used in the termination of fire-resistant cables into equipment should not compromise the defined performance of the cables in the presence of the potential hazards.

e) Cable joints should be avoided where possible and minimized in their use. Where conditions require that a joint be used, it should be of a type that has similar performance to the cable in the presence of the potential hazards.

f) The cable fixing should be in accordance with the cable manufacturer’s recommendations and preclude the use of non-metallic cable clips, cable ties and cable trunking as the sole means of support for the cables, for example, plastic, nylon and aluminium cable cleats would not normally be deemed suitable. g) The cable fixing centres should be within the cable manufacturer’s recommended maximum spacings for both the vertical and horizontal runs. The adverse effects of expansion, contraction and vibration should also be in accordance with the manufacturer’s recommendations.

h) Cables should, wherever practicable, be installed upon the dedicated cable support system. Where this is impractical due to the nature of the installation, the cable fixing should be carefully selected to achieve the fire performance required of the cables to be supported. i) j)



Cables installed within vertical risers and cable enclosures with straight runs over 32 m should incorporate an offset of two cable diameters to provide strain relief from the vertical weight of the cable.

Designers and installers should follow the installation practices recommended by the material suppliers and equipment manufacturers when designing and installing the cables and their associated support systems, as under fire conditions, cables and the associated support systems can collapse and block the means of escape.

16 Cable support systems

The support system should have a fire survival time equal to that of the cables it supports and for the same defined fire conditions. When sizing the brackets for support systems intended to carry fire-resistant cables in a fire condition and where the circuits are to maintain their circuit integrity under defined fire conditions for a predetermined period, the support system should be adequately sized to account for the fact that the strength of steel is significantly reduced in a fire situation.

NOTE 1 Failure to observe the design criteria can result in premature collapse of the cable support system and the circuit failure of the cables being supported.

If mild steel drop rods are to form the suspension element of the support system, their cross-sectional area should be determined in accordance with Annex E. NOTE 2 This British Standard does not preclude the use of alternative support systems to threaded rod and steel bearers, such as wire suspension systems or direct fixings to the structure or custom-fabricated supports, where it can be clearly demonstrated by appropriate testing that they offer the required fire survival performance.

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The selection of the fixing anchors should be treated as equally as important as the design of the cable support system. Where practicable, the fire-resistant route should be arranged to be one of the upper tiers of the coordinated high-level services.

NOTE 3 When coordinating the route for the fire-resistant cables, it needs to be recognized that some of the other services, such as pipes, ducts, busbars and other cable routes, are unlikely to be designed to maintain their fire integrity (for the same duration) under fire conditions and could collapse during a fire. The result of the collapse could be the overloading of the fire-resistant cable support system, which itself could then fail.



To maximize the fire integrity of the fire-resistant cable system, fire-resistant and non-fire-resistant cable support systems should be separate and, if following the same route, the fire-resistant cable support system should, where practicable, be installed above the non-fire-resistant cable support system.

17 Junction boxes and joints 17.1 Power cables

The installation of joints in cables, other than those contained within the electrical equipment enclosures, should be avoided wherever practicable.

Where the life safety, fire-fighting or other critical circuits require the use of joints or junction boxes to house terminations and other critical system components, they should provide the same level of fire performance as that offered by the cable.

The test protocol should be based on the test methodology described in BS 8491, which incorporates the elements of fire, mechanical impact and water spray on to a single test sample, with the impact being applied directly to the junction box or joint. The sample junction box or cable joint should be securely fixed to the standard test ladder, defined in BS 8491, at the point of the flame impingement, mechanical impact and water jet application. The junction box or joint test sample should incorporate two lengths of fire-resistant cable and, where required, incorporate appropriately IP-rated cable glands. The method of cable termination should be in accordance with the cable manufacturer’s installation instructions and should also include the necessary shrouds, gaskets, terminations and other required equipment to form part of the fire test.

NOTE 1 The intent of this recommendation is not to stifle innovative solutions so long as the level of fire and water ingress integrity is maintained, and any alternative solution is agreed with the cable manufacturer in writing.

The electrical continuity of the two lengths of cable and the terminations should be monitored throughout the test for their circuit integrity in accordance with BS 8491.

The sample should be evenly heated via the standard horizontally-mounted ribbon burner to a temperature of 842 °C for a period of 120 min.

The mechanical impact device should be in accordance with BS 8491 with the impact applied directly to the sample junction box or joint under test. The impact should be applied every 10 min throughout the test duration. The water jet should be applied 5 min from the end of the test duration, comprising 5 s bursts every 60 s for the last 5 min of the test, in accordance with BS 8491. A complete junction box assembly should maintain an IP rating of IP56 and a completed joint assembly should have a type approval in accordance with BS EN 50393. 20 © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED

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NOTE 2 It is not the intention of this recommendation that the IP test forms an integral part of the fire integrity test for the junction box assembly.

A detailed test report should be provided at the conclusion of the test, in accordance with BS 8491, including a detailed description of all of the components of the test sample and how they have been assembled, including cables, junction box or joint, terminals, cable glands, shrouds and gaskets.

The selected terminals should be suitable for the fire test temperatures likely to be experienced; typically, ceramic terminals are used to maintain circuit integrity under fire conditions. Where internal equipment such as power supplies, fire alarm interface modules and relays, have a maximum operating condition, this should be monitored and recorded as part of the test protocol and, where necessary, the appropriate additional thermal protection provided. The maximum permitted internal operating temperature and the associated temperature rise above ambient should be determined based on the specific temperature limits of the equipment to be accommodated within the junction box and should be as defined by the equipment manufacturer.



17.2 Control cables

Where the circuit integrity of control cables might affect the availability or operation of fire life safety equipment, the recommendations of 17.1 should be followed for control cables, using the relevant test methods for each category described in Clause 11.



18 Fire-resistant busbar systems

Where a cast resin busbar has been specified in high-rise commercial offices for electrical distribution feeding life safety and fire-fighting equipment, the busbar should comprise compact, low impedance copper conductors, encapsulated in cast epoxy resin. The busbar products should be tested in accordance with BS 8602 where the busbar systems are intended to supply life safety and fire-fighting equipment. NOTE



The test standard is applicable to cast resin busbar trunking of rated voltage not exceeding 1 000 V.

19 Areas of special fire risk COMMENTARY ON CLAUSE 19 Research has confirmed that where there are ventilation limitations and/or very large fire sizes (e.g. in underground car parks and loading bays), temperatures can reach as high as 1 200 °C. Such areas therefore need special consideration. Areas that can be classified as areas of special fire risk include: •

high bay warehouses;

•

underground car parks; 5)

•

hydrocarbons fuel storage; and

•

loading bays;

•

large basement storage;

•

self-storage buildings/units.

Further information on areas that could be classified as areas of special fire risk is given in BS EN 12845.



5)

As a general principle, cables for life safety, fire-fighting or other critical systems should not be installed within areas of special fire risk. However, where this cannot be avoided, the cables used

BRE Fire Spread in Car Parks report dated 16th February 2009.

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should be Category 3 cables as defined in Clause 11 and should be additionally protected and designed for the specific risk identified. Protective systems may be used, but the designer should take account of the revised thermal conditions into which the cable is to be installed and the resulting impact on the cable’s installed rating (IZ) when installed in an insulated enclosure. Fixings should have suitable protection, appropriate for the anticipated maximum temperatures.

20 Life safety and fire-fighting applications 20.1 Sprinkler and wet riser pumps

Sprinkler pump installations should be designed and installed in accordance with BS EN 12845. Wet riser pump installations should be designed and installed in accordance with BS 9990.

To enable the designer to correctly size both the primary mains supply and the secondary generator supply, the pump/motor manufacturer should provide the following motor parameters along with the appropriate pump/motor data sheets: •

pump rating, kW;

•

voltage, V;

• • • • • • • • • • •

method of starting, star/delta, soft start; voltage (min), V;

full load current, A; starting current, A;

duration of star phase, s;

starting current (delta), A; duration of delta phase, s; starting power factor;

locked rotor current star, A; hot burn-out time, s; and starter fuse selection.

The manufacturer should provide the time/current characteristic for the proposed motor/pump combination, identifying the predicted load/torque characteristics of the pump installation and providing the motor load current in amps from standstill, through the star/delta starting conditions to steady-state plotted against time in seconds. Under normal conditions, the duty pump should start first in response to the initial drop in system water pressure and the standby pump should start if the system water pressure continues to fall. While the two sprinkler pumps are unlikely to be called for at the same time this scenario should be accommodated by the designer.

The designer should also take account of the following scenario under both mains and life safety generator supply conditions: one of the fire pumps experiencing a locked rotor condition, where the mains supply and life safety generator would be required to supply the locked rotor current until the associated protective device operates, and the starting current of the assist pump. The sprinkler pump protective device (fuse) should be selected by the fire pump motor starter supplier to ensure that it can carry the locked rotor current for a period of not less than 75% of the hot burn-out time of the motor. 22 © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED

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The designer should coordinate the upstream protective device (fuse) to match the motor starter fuse to ensure that it cannot operate before the motor starter fuse. NOTE Full selectivity is not deemed necessary where the protective device feeds a single sprinkler or wet riser pump.



The cable feeding the fire pumps should then be sized, based on the upstream protective device.

20.2 Smoke control systems

Smoke clearance and control systems should be designed and installed in accordance with BS 7346 (all parts) and the BS EN 12101 series. They should maintain their operation to protect and assist the fire and rescue service, as part of the building’s active fire-fighting systems, for a minimum period of 60 min, depending on the specific application. The power supplies should be provided in accordance with the applicable recommendations of this British Standard and the requirements of BS EN 12101‑10. Variable speed drives (VSDs), which are commonly used where a range of duties are required from the smoke control system, should be designed to be compatible with power cables indicated in Clause 11 and in accordance with BS 7671. Where the smoke control system comprises a run and standby fan configuration, separate inverter drives should be provided to each fan motor.

The designer should establish from a risk assessment whether the specific smoke control application requires the provision of an inverter bypass, and whether it is necessary to maintain the fire-fighting function in the event of periodic inspection and testing of the VSD equipment. Where a smoke control system has a fire-fighting interaction or override (where a firefighter can change the status of the smoke control system), it is classified as a Category 3 system and both the power and control cables should have a 120 min fire survival time.

NOTE BS 7346‑8 specifies requirements for avoiding routing smoke ventilation system power supply cables through high-risk areas such as car parks, where extreme temperatures can be encountered under fire conditions.



The components for multi-zoned smoke ventilation systems using smoke detector operated smoke/ fire dampers should be protected against fire throughout the system.

20.3 Car park smoke control systems

NOTE 1  BS 7346‑7 provides recommendations for smoke and heat control systems serving covered car parks and designed for one or more of the following: a) to assist firefighters to clear smoke from a car park during and after a fire; b) to provide relatively smoke-free access for firefighters to a point close to the seat of the fire; and/or c) to protect means of escape from the car park.

The main car park extract fan control panel should be located in the same fire-resisting building fabric enclosure as the run and standby extract fans, fed by an ATS located in the same building fabric enclosure. The ATS should be fed by diversely routed primary and secondary sources of supply, utilizing Category 3 cables, which should, where practicable, be routed away from the car park area served by the smoke clearance system. Where impulse/jet fans are installed as part of the smoke clearance system, their source of supply should originate from the same protective building fabric enclosure as the smoke extract fans and may be fed by a common ATS provided it is rated accordingly.

The impulse/jet fan supply cables should be selected to be Category 3 as they are likely to be exposed to the elevated temperatures in a fire condition in the car park. © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED 23

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NOTE 2 It is not considered necessary to provide a separate ATS local to each of the impulse/jet fans.



20.4 Firefighters and evacuation lifts Power supplies to firefighters lift installations should be equipped with primary and secondary power supplies, and be fire-resistant for a minimum period of 120 min. The supplies should be designed and installed in accordance with BS EN 81‑72.

The secondary power supply should be rated to run the firefighters lift at rated load and rated speed for a period of 120 min.

In the event of a mains or sub-mains power supply failure the ATS should detect loss of the supply, signal the life safety generator to start and automatically change over to the secondary supply. When power is re-established the firefighters lift should become available for service within one minute. The designer should establish from the lift supplier whether the proposed equipment incorporates regenerative braking, by which the lift installation is capable of exporting energy back into the electrical distribution system. NOTE 1 Life safety generators are typically limited in their ability to absorb regenerative energy.

Evacuation lifts are utilized to provide an organized and controlled movement of persons from a dangerous place to a safe place; they should be provided with a primary source of supply from a dedicated sub-main circuit to the evacuation lift.

NOTE 2 Other lifts in the same well may be fed from the same primary supply, provided it is rated accordingly and a fault on another lift cannot affect the operation of the evacuation lift.

Evacuation lifts should be designed, installed and operated in accordance with BS 9999:2017, Annex G and BS 9991 to maintain their operation during a fire condition, as well as for the evacuation of people who find other evacuation routes difficult in the event of a fire. NOTE 3 BS 9999:2017, G.2.2 allows, subject to risk assessment taking account of a number of factors, the provision of two protected and diverse power supply circuits to the lifts from a single supply intake to the building, unless a secondary supply is provided for other life safety reasons (e.g. to power firefighters lifts or smoke control fans), in which case it is preferred that the evacuation lifts be connected to both these supplies.

The primary and secondary fire-resistant (Category 2) supply cables should be: a) diversely routed through areas of low fire risk; and b) physically protected against damage.

Isolators and protective devices feeding the evacuation lift should be labelled accordingly.

NOTE 4 Battery inverter supplies are not normally acceptable as the alternative secondary source of supply.

The switchrooms providing the source of supply and the lift machine rooms should be fire-resistant building fabric enclosures.

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Annex A (informative) Selection and specification of UPS/battery inverter systems to serve as the secondary source of supply to life safety, fire-fighting and other critical systems

A.1 General UPS/battery inverter systems may be considered as an alternative secondary source of supply to a conventional standby generator, feeding life safety and fire-fighting systems, based on the recommendations of BS 9991 for residential buildings.



The selection and specification of the equipment is important in order that the UPS is capable of supplying the critical load characteristics, for both steady-state and transient conditions, for the required period or fire survival time.

A.2 UPS equipment

UPS equipment has been developed for the supplies to business-critical IT equipment for relatively short autonomy periods, typically 10 min to 30 min, and not to support life safety and fire-fighting equipment for fire survival times measured in hours. In order to provide the required operating time the battery installation is sized accordingly, which requires the rectifier/charger components of the UPS to be uprated to enable them to recharge the enlarged battery in the specified time period. The enlarged battery represents a further challenge: the battery recharge time required to recharge a fully discharged battery to 100% charge. Typically, this is a period of approximately 12 h to reach 80% and 24 h to reach 100% charge. During this extended recharge time, the occupants of the building are not fully protected by the UPS equipment. By comparison, it is feasible for a life safety generator to refuel in 3 h, where necessary. The life safety and fire-fighting loads are commonly pump and fan motor loads, which are largely inductive; these generate increased starting currents for a duration measured in seconds. Whilst having a minimal impact on the size of the battery, these transient conditions are important when sizing the UPS rectifier/charger to ensure the equipment is capable of supporting the load.

The selection of sprinkler and wet riser pump power supplies requires the locked rotor condition to be accounted for where electrically driven pumps are being installed; these transient conditions affect the rating of the UPS equipment.

The overload and short circuit characteristics of the life safety and fire-fighting loads also have to be accounted for and the UPS equipment sized accordingly. The UPS equipment often has to rely on the static bypass of the UPS equipment in order to supply the required magnitude of fault current to trip the downstream protective devices. This is not an issue when the UPS equipment is operating on a healthy mains supply for normal UPS business critical applications, where the bypass is available. However, when the UPS equipment is supplying life safety and fire-fighting equipment it is required to support the critical load for extended periods when the mains primary supply fails and therefore the UPS bypass facility is unavailable to clear a fault condition. The UPS rectifier/inverter path is rated to cater for the fault clearing requirements of the largest downstream protective device. Where the UPS equipment is to supply lift(s), negotiation between the building designer and lift provider defines whether the lift equipment is capable of regenerative braking, resulting in the lift

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equipment generating power flow back into the UPS equipment under certain conditions. The UPS selection is required to take account of this by dissipating the back-fed energy, preventing damage to the UPS equipment. The UPS and battery equipment requires ongoing maintenance, consisting of: •

complex power electronics;

•

supplementary cooling equipment.

•



DC power installation; and

By comparison, the maintenance requirements for a life safety generator consist of engine and alternator general mechanical, and electrical maintenance activities.

A.3 Battery selection

The batteries for UPS equipment may utilize a number of alternative battery technologies, including: •

valve-regulated sealed lead acid (VRLA);

•

wet cells (Plante); and

• •

nickel cadmium; lithium ion.

VRLA batteries are the most common and cost-effective technology, specified in accordance with BS EN 60896‑21 and BS EN 60896‑22. When installed, they typically achieve a life expectancy of 7 years to 10 years, when maintained at their optimum ambient temperature of 20 °C. At the end of life, the battery capacity reduces to approximately 80% of the initial capacity and is factored into the sizing calculation if the battery is to achieve the fully-specified capacity equivalent to the fire survival time at the end of life. To optimize the life expectancy of the battery, the battery ambient temperature is required to be controlled to 20 °C, as operating the battery at elevated temperatures significantly reduces the life expectancy: 1) operating at 30 °C: life expectancy typically 5 years;

2) operating at 35 °C: life expectancy typically 2 years to 2.5 years.

This factor requires the plant room accommodating the UPS and battery equipment to be air conditioned by suitably resilient cooling plant and associated power supplies, whereas by comparison the standby generator requires a ventilated plant room. Equally important is to protect the UPS battery from very low temperatures as this adversely affects the battery performance.

A UPS application with a typical autonomy time of 10 min to 30 min could have the associated air conditioning plant supported by a generator in the event of a mains supply failure and not by the UPS system, relying on the thermal inertia of the room volume to maintain the UPS equipment within acceptable conditions. UPS equipment installed as an alternative secondary source of supply instead of a standby generator, required to operate for extended autonomy times in the event of mains failure, requires the air conditioning plant to be supported from the UPS equipment and dual redundant cooling units might also be necessary. BS EN 12101‑10 calls for a standby generator required to support life safety and fire-fighting equipment to be equipped with 4 h, 8 h or 24 h of fuel storage; this level of UPS autonomy period would be difficult to achieve. 26 © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED

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Annex B (informative) Typical high voltage (HV) circuit in a building The example shown in this annex is for a circuit with the following characteristics: 11 kV a.c. 3 phase, 1 000 kVA and a 1 s fault of 14 kA using a 3-core copper conductor cable conforming to BS 7835 installed in a cable protective enclosure. Amperes per phase can be determined using the parameters taken from the example [kVA = 1 000, VL = 11 000 (phase to phase voltage)] using the following equations. kVA=

1 × VL × 3 (B.1) 1 000

kVA × 1 000 V× 3

= I (B.2)

1 000 × 1 000 11 000 × 3

= 52.5 A

Frequently, when HV circuits have a relatively low current requirement, sizing of the cable is determined by the short circuit limits.

(B.3)

The minimum conductor size that can safely carry a 14 kA fault for 1 s is 120 mm2, which has a fault rating of 17.2 kA for 1 s. A 120 mm2 conductor has a sustained current rating, at 25 °C ambient temperature, of 390 A when installed in free air. When installed in a thermally rated fire trunking system, the in free air rating is corrected by 0.5, so its rating is 390 × 0.5 = 195 A. This is more than adequate for the circuit.

Dependent on the earthing arrangements, the armour might also be required to carry a 14 kA fault for 1 s. The minimum size cable that has sufficient armour to carry the fault current is a 3-core 185 mm2 cable that can carry 14.2 kA for 1 s. The rating of this cable when installed in a thermally rated fire-resistant cable protective system is 505 × 0.5 = 252 A, which again is more than adequate for this circuit. The sizing of the cable for any circuit is determined by several factors; current rating is only one of them and, as in the example given, not the determining one.

Current rating of cables in air and 1 s fault ratings can be found in cable manufacturers’ data sheets.

Annex C (informative) Performance criteria for cable protective systems The performance of the system is assessed in accordance with the general methodology described within BS EN 1366‑5 for fire integrity and thermal insulation under furnace exposure conditions for fire outside of the cable protective enclosure. The protective system performance criteria after 120 min is given in BS EN 1366‑5. NOTE

Further information on the cable protective systems in BS EN 1366‑11 is given in Annex H.

The 2003 edition of BS EN 1366‑5 was updated and revised in 2010, which included revisions to Figure G.1, relating to the required location of the T3 thermocouples. For this reason, a copy of the © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED 27

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original 2003 version of Figure C.1 has been included within this annex to ensure that they are located midway along the test sample, on the internal face of the cable protective system, as indicated. The location of the thermocouples do not coincide with the joints in the cable enclosure. The cable protective systems are designed and constructed so that after testing they resist the ingression of water, possibly from firefighters’ hose streams or sprinkler activation. Cable protective systems constructed from non-permeable materials such as steel, which can contain internal insulation materials, are not adversely affected by water impingement from sprinkler or fire hose activities.

In addition, for a judgement to be made on the potential adverse effects on the cables enclosed within the duct or shaft, the surface temperature recorded by the thermocouples located inside the cable protective system (T3) does not exceed 180 °C above the initial mean temperature. Also, loadbearing capacity (stability) is assessed as the ability of the enclosure within the furnace to fulfil its intended function for the specified time. Failure of the stability criteria is deemed to have occurred when the suspension or fixing devices can no longer retain the duct or shaft in its intended position, when sections of the duct or shaft collapse or when cracks, holes or other openings through which flames pass are evident.

Figure C.1 — Example of test arrangement for horizontal service ducts (fire exposure from outside), adapted from BS EN 1366-5:2003

Dimensions in millimetres

Key a) Optional fan and extract hood

d) Interior thermocouples positioned as for the large duct

 

 

b) Suspension devices c)

Furnace  

e) Furnace walls f) Furnace roof  

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Annex D (normative) Testing of Category 3 cables of core sizes up to and including 4 mm2 cross-sectional area COMMENTARY ON ANNEX D This annex recommends a method of test to be used for small cables where the requirements of BS EN 50200 are modified to use a flame temperature of



(930

water spray.

+40 ) °C and the application of 0

D.1 Duration of survival

D.1.1 Time













The duration of the test should be 120 min (115 min for the initial fire and impact phase followed by an additional 5 min for the fire, impact and water phase), during which the cable should not reach the point of failure.

D.1.2 Point of failure

The point of failure should be in accordance with BS EN 50200.

D.2 Test environment

The test environment should be in accordance with BS EN 50200.

D.3 Test apparatus

The test apparatus should be in accordance with BS 8434‑2.

D.4 Verification procedure for source of heat

The verification procedure should be in accordance with BS 8434‑2.

D.5 Test sample

The test sample should be in accordance with BS EN 50200.

D.6 Cable test procedure D.6.1 General

The general test procedure should be in accordance with BS EN 50200.

D.6.2 Procedure for different cable types

The procedure for different cable types should be in accordance with BS EN 50200.

D.6.3 Ignition and shock production

Ignition and shock production should be in accordance with BS EN 50200. © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED 29

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D.6.4 Electrification or optical monitoring Electrification or optical monitoring should be in accordance with BS EN 50200.

D.6.5 Application of water spray

After 115 min exposure in accordance with D.6.3, with the flame and shock still being applied, start the water spray in accordance with the method described in BS EN 50200:2015, Annex E. Continue applying the water until the end point of the test.

If the application of the water extinguishes the flame then, for safety reasons, the gas supply should be turned off and the test should be considered invalid.



The point of failure should be as defined in D.1.2.

D.7 End point

The test should be continued either:

a) until 115 min of fire and impact alone, followed by 5 min of fire, impact and water (total 120 min) has been completed; or



b) to the point of failure as defined in D.1.2.

D.8 Test report

The test report should be in accordance with BS 8434‑2.

Annex E (normative) Determining the cross-sectional area of drop rods COMMENTARY ON ANNEX E This annex is based on the guidance in BS EN 1366‑5. The purpose of this annex is to measure the ability of ductwork systems to resist the spread of fire from one fire compartment to another without the aid of dampers. This annex refers to a complete ductwork installation and therefore includes joints, supports and the fire stopping through the furnace wall. The support elements for ductwork systems are similar to those used to support cable support systems, i.e. anchors, drop rods, horizontal channel bearers, nuts and washers, and have therefore been used as a basis for the recommendations given in this annex. This annex assumes that the mechanical load is evenly distributed on the support system bearers and the two suspension threaded drop rods on each bearer are equally loaded. This might not be the case for the cable support system or the cable protective system and this is to be accounted for, either by stipulating that the cables installed on the support system be installed in such a way as to ensure even loading of the bearers or an additional safety factor included to account for the uneven load distribution. NOTE 1 Further guidance on the calculation of the mechanical loading applied to the drop rod and bearer assemblies is given in Annex I.

The cable systems should contain a spare capacity allowance for future system extension in the region of additional 20% to 30%; this should be confirmed in the relevant project requirements and taken into account when analysing the support system loadbearing ability in fire. 30 © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED

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Furthermore, the recognized practice of installing double nuts on the threaded rods should also be incorporated to reduce the risk of premature collapse due to the failure of a single nut under fire conditions.

NOTE 2 This annex does not preclude the use and installation of other suspension systems, such as wire suspension systems and pre-manufactured channel support systems, provided that they can be clearly demonstrated to have appropriate fire survival characteristics.

The cross-sectional area of the drop rods should be calculated using the following formula (E.1): A=

where:  

A

 

Lb

 

Wb

 

ςmax

 

h

 

W

     

Lh

Wr

WT

(W × Lh + WT × Lh + Wb × Lb + 2Wr × h) × 9.81 2 × ς max



(E.1)

is the cross-sectional area of the drop rod, in square millimetres (mm2);

NOTE If the drop rod is a threaded rod then A is based on the minor diameter (see Figure E.1). is the height of drop rod, in metres (m); is the length of bearer, in metres (m);

is the distance between hanger supports, in metres (m);

is the weight of cables per metre, in kilograms per metre (kg/m);

is the weight of bearers per metre, in kilograms per metre (kg/m);

is the weight of drop rods per metre, in kilograms per metre (kg/m);

is the weight of the cable protective system, cable tray or ladder rack per metre, in kilograms per metre (kg/m); is the maximum allowable stress, in newtons per square millimetre (N/mm2).

NOTE 3 Any additional loading to the support system, for example, from other services on combined services bracketry or multi-service modules, is also to be taken into account when calculating the total load on the drop rods. NOTE 4 The elements of the cable support system are shown in Figure E.1 and Figure E.2.

Figure E.1 — Typical thread detail identifying the major and minor diameters

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Figure E.2 — Elements of the cable support system

Key 1 2

Drop rod Cable

3 4

Cable tray or ladder Bearer

Using information published by manufacturers of fire-rated ductwork, unprotected drop rods and bearers made of mild steel should be sized such that the calculated stresses do not exceed the values given in Table E.1.

Table E.1 — Maximum allowable stress of steel drop rods in fire conditions Fire duration

Maximum allowable stress(ς max)

H

N/mm2

2

6

0.5 1

9 9

The threaded rod should satisfy the parameters set out in BS 3643‑1 and BS 3643‑2.

The details included in Table E.2 are intended to be indicative, and the designer should identify the specific type of threaded rod to be installed and the relevant performance data.

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Table E.2 — Typical metric thread details (assumed to be coarse pitch) Rod designation

Minor diameter (External) BS 3643‑2:2007

M8

6.200

M16

13.181

M10 M12 M20

Nominal area mm2

7.858

30 min (9 N/mm2)

60 min (9 N/mm2)

120 min (6 N/mm2)

30.2

27.70

27.70

18.47

136.5

125.19

125.19

83.46

48.5

9.516

71.1

16.529

Max. static vertical load/kg /drop rod

214.6

44.49 65.25

196.86

44.49 65.25

196.86

29.66 43.50

131.24

NOTE In practice the drop rods are generally installed in pairs, such as when used with a steel channel bearer, therefore the potential load capacity will be double for a cable support system, provided the load is evenly distributed on the bearer.

Annex F (informative) Example voltage drop calculations for cables in a fire COMMENTARY ON ANNEX F As a rule of thumb, increasing the required cable conductor size by two sizes (as in the example of Annex F) is considered to provide adequate protection. In order to calculate the voltage drop of a cable in a fire, the following factors need to be known or assumed: a) total cable length;

b) current to be carried;

c) voltage drop per amp per metre of cable at 90 °C;

d) correction factor for voltage drop from 90 °C to cable temperature in the fire; e) temperature of that part of the cable that is in the fire; and f) length of that part of the cable that is in the fire.

The following correction factors are based on a copper conductor with a temperature coefficient of 0.003 93 °C: •

90 °C to 650 °C = 2.726 0;

•

90 °C to 850 °C = 3.342 4;

• •

90 °C to 750 °C = 3.034 2; 90 °C to 950 °C = 3.650 6.

For example, the first factor is calculated by: 1 + 0.003 93( 650 − 20 ) = 2.726 0 1 + 0.003 93( 90 − 20 )

The process of calculating the voltage drop of a cable under given operating conditions is normally straightforward. The manufacturer’s tabulated values of voltage drop per amp per metre are multiplied by the length of run and current to be carried, to give the expected voltage drop.

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The manufacturer’s tabulated values assume that the cable conductor temperature is at its maximum permitted operating temperature. If the cable is involved in a fire, the conductor temperature and hence the resistance is higher, therefore the voltage drop would be higher.

The problem in determining the voltage drop for a run of cable in a fire is not knowing the conductor temperature at each point along its length. Therefore assumptions have to be made in calculating what the voltage drop would be. To illustrate the effect of assuming different lengths of cable being involved in a fire, two sets of examples are given, one based on 5 A and the other based on 200 A load. a) Example 1.0

Assume a 2-core 2.5 mm2 cable conforming to BS 7846, carrying 5 A over 50 m. In normal operation the voltage drop would be: 19 × 0.001 × 5 × 50 = 4.75 V.

The voltage drop per amp per metre for this cable is 19 mV. b) Example 1.1

Assume a 2-core 2.5 mm2 cable conforming to BS 7846, carrying 5 A over 50 m. Assume 2 m are at 750 °C and the rest of the cable is at 90 °C. The voltage drop would be:

(19 × 0.001 × 5 × 48) + (19 × 0.001 × 3.034 2 × 5 × 2) = 5.14 V.

The voltage drop per amp per metre for this cable is 19 mV.

The correction factor from 90 °C to 750 °C for copper (Cu) is 3.034 2. c) Example 1.2

Assume a 2-core 2.5 mm2 cable conforming to BS 7846, carrying 5 A over 50 m. Assume all 50 m are at 750 °C. The voltage drop would be:

19 × 0.001 × 3.034 2 × 5 × 50 = 14.41 V. The voltage drop per amp per metre for this cable is 19 mV.

The correction factor from 90 °C to 750 °C for copper (Cu) is 3.034 2. d) Example 2.0

Assume a 2-core 120 mm2 cable conforming to BS 7846, carrying 200 A over 50 m. In normal operation the voltage drop would be: 0.42 × 0.001 × 200 × 50 = 4.2 V.

The voltage drop per amp per metre for this cable is 0.42 mV. e) Example 2.1

Assume a 2-core 120 mm2 cable conforming to BS 7846, carrying 200 A over 50 m. Assume 2 m are at 750 °C and the rest of the cable is at 90 °C. The voltage drop would be:

(0.42 × 0.001 × 200 × 48) + (0.42 × 0.001 × 3.034 2 × 200 × 2) = 4.54 V.

The voltage drop per amp per metre for this cable is 0.42 mV. 34 © THE BRITISH STANDARDS INSTITUTION 2020 – ALL RIGHTS RESERVED

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The correction factor from 90 °C to 750 °C for copper (Cu) is 3.034 2. f) Example 2.2

Assume a 2-core 120 mm2 cable conforming to BS 7846, carrying 200 A over 50 m. Assume all 50 m are at 750 °C. The voltage drop would be:

0.42 × 0.001 × 3.034 2 × 200 × 5 = 12.74 V.

The voltage drop per amp per metre for this cable is 0.42 mV.

The correction factor from 90 °C to 750 °C for copper (Cu) is 3.034 2.

As can be seen from these examples, although the voltage drop has increased from normal operation, with part or all of a cable in a fire, the percentage drop from a 240 V single phase supply does not increase significantly. That is to say: Example 1 would give 1.98%, 2.14% and 6% respectively. Example 2 would give 1.75%, 1.9% and 5.3% respectively.

From these percentage volt drop values, it would seem unlikely that a fire would have a significant effect on most equipment being supplied by the cable, even in the example of the worst case given above.

However, if it is required to limit the volt drop to 4% for the example when the whole length of cable is in a fire, e.g. motors running, fire-fighting water pumps, then the cable sizes in Examples 1.2 and 2.2 would have to be increased from 2.5 mm2 to 4.0 mm2 and 120 mm2 to 185 mm2 respectively. g) Rework of Example 1.2 but with a 4.0 mm2 cable

The voltage drop would be: 12 × 0.001 × 3.034 2 × 5 × 50 = 9.1 V. The voltage drop per amp per metre for this cable is 12 mV. The correction factor from 90 °C to 750 °C for copper (Cu) is 3.034 2. On a 240 V circuit the voltage drop would be 3.8%. h) Rework of Example 2.2 but with a 185 mm2 cable

The voltage drop would be: 0.29 × 0.001 × 3.034 2 × 200 × 50 = 8.8 V. The voltage drop per amp per metre for this cable is 0.29 mV. The correction factor from 90 °C to 750 °C for copper (Cu) is 3.034 2. On a 240 V circuit, the voltage drop would be 3.7%.

From the above it is possible to calculate the voltage drop for cables involved in a fire by assuming the cable temperature in a fire and cable length affected, following the examples previously given. In most cases it is unrealistic to assume that all of the cable length is involved in a fire. If a cable size was selected for a maximum of 2% voltage drop in normal operation, the voltage drop of this cable would be a maximum of 4%, even assuming 950 °C.

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Annex G (informative) Fire-resistant cables under fire and fault conditions The melting temperature of copper is 1 083 °C. Therefore, if a copper conductor in any cable reaches 1 083 °C, it will melt and no longer function. As an example, cables conforming to BS 7846 operating under normal conditions are designed to have a maximum continuous conductor temperature of 90 °C, which is the combination of ambient temperature and temperature rise due to carrying current. These cables are suitable for a normal overload temperature of 250 °C based on their reuse and the fact that they have thermosetting insulation (e.g. XLPE). The temperature rise of 160 °C (90 °C to 250 °C) is based on the conductor carrying 143 A/mm2 for 1 s. This current is based on the standard ohms law: If =

V Z e + R1 + R 2

where:  

If

 

R2

Ze

 

R1

 

is the fault current, in amps (A);

is the input impedance of the system, in ohms (Ω);

is the resistance of the line conductor at average fault temperature, in ohms (Ω);

is the resistance of the earth fault path at average fault temperature, in ohms (Ω).

During a fire, the fault current obtained is lower than under normal operating conditions, as both R1 and R2 are greatly increased due to their resistance being based on a much higher temperature. Temperature correction factors for copper are shown in Table G.1.

Table G.1 — Temperature correction factors for copper Temperature

Correction factor

°C 20

1.0

250

1.904

90

170 650 750 800 850 900

1.275 1.590 3.476 3.869 4.065 4.262 4.458

It is extremely difficult to calculate the potential fault current of a cable when it is in a fire because much of the information required is not known exactly, such as the temperature of the cable at the fire, the length of cable involved in the fire, and the temperature of the cable not involved in the fire. However, the temperature rise, due to a fault because R1 and R2 are higher than normal, will not exceed 160 °C and quite possibly be significantly lower. Therefore, taking into account copper’s melting temperature of 1 083 °C, and assuming a maximum rise due to a fault of 160 °C, providing the temperature of the copper conductor before fault is less than approximately 900 °C, the copper conductor is not expected to be at its melting temperature. NOTE In most circumstances, increasing the required cable conductor size by two sizes (as in the example of Annex F) is considered to provide adequate protection.

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Annex H (informative) Cable protective systems to BS EN 1366‑11 The content of BS EN 1366‑11 is unsuitable for complying with the recommendations of BS 8519 to provide fire protection to the primary and secondary power supply cables to the life safety, fire‑fighting and other critical loads.

BS EN 1366‑11 permits and encourages the use of two and three‑sided cable protective systems, installed against the building's structural elements, such as walls and soffits, where the joint interface with the building structure forms a critical element of the cable protective system. Two and three‑sided cable protective systems are not permitted by BS 8519 for this reason.

BS EN 1366‑11 is based on cable protective systems that are fabricated on site from fire-resistant material, being custom-built for each installation. BS 8519 calls for the cable protective system to be assembled from factory-manufactured components, utilizing simple standard components where the joints are less dependent on the workmanship of the installer on site. Other differences between BS EN 1366‑11 and BS 8519 include the following.

a) BS EN 1366‑11 makes no reference to the need for the cable protection system to maintain the fire integrity in the presence of water from either sprinklers or a fireman's hose, as recommended by BS 8519. b) BS EN 1366‑11 makes reference to ventilators and venting of the enclosure, which are not recognized by BS 8519.

Annex I (informative) Guidance on calculating the mechanical loading on the drop rods Where the loads on a simple trapeze bracket are not evenly distributed, the load share experienced by each drop rod can be calculated using the following method. The load on drop rod B can be calculated using the following formula (I.1): Load at B =

where:    

Ln

dn

Therefore:

( L1 × d1 ) + ( L2 × d 2 ) + ( Ln × d n ) distance between supports

(I.1)

is total weight of the service per metre (kg/m) multiplied by the distance between each bracket; and is distance of the load from drop rod A, in metres (m)

Load at B =

(52 × 0.15) + (7 × 0.55) 0.8

= 14.6 kg

Load at A = Total Load – Load at B = 59 – 14.6 = 44.4 kg

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The point loads in Figure I.1 represent the centre line of the electrical cables on the bearer/ containment assembly. Where the ladders or trays themselves are unequally loaded, Formula (I.1) can be used with the weights and distances of individual cables, remembering to add in the weights of the ladder/tray/basket and the allowance for any additional spare capacity.

Figure I.1 — Example of mechanical loading on the drop rods

Annex J (informative) Variation from the recommendations of BS 8519:2020 BS 8519 is a code of practice; its contents take the form of recommendations, rather than requirements. The recommendations are primarily based on recognized good practice in the design and installation of the power supplies serving life safety, fire-fighting and other critical systems. There are, however, applications in which the recommendations would be difficult or impossible to implement. In these circumstances, variations from the recommendations might be necessary, even though, in general, the user, purchaser, enforcing authority or insurer requires strict compliance with the standard.

This does not imply that the designer or installer has freedom to ignore the recommendations of this standard under the circumstances in which a user, purchaser, enforcing authority or insurer seeks compliance with it. Variations need to be the subject of specific agreement amongst all interested parties and need to be identified in all relevant system documentation (see Figure J.1).

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Figure J.1 — Model completion certificate — Design — Declaration of conformity

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Bibliography For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Standards publications

BS 7629‑1, Electric cables — Specification for 300/500 V fire resistant, screened, fixed installation cables having low emission of smoke and corrosive gases when affected by fire — Part 1: Multicore cables BS 7846, Electric cables — Thermosetting insulated, armoured, fire-resistant cables of rated voltage 600/1000 V for fixed installations, having low emission of smoke and corrosive gases when affected by fire — Specification BS 7974, Application of fire safety engineering principles to the design of buildings — Code of practice BS EN 1366‑5, Fire resistance tests for service installations — Part 5: Service ducts and shafts

BS EN 1366‑11, Fire resistance tests for service installations — Part 11: Fire protective systems for cable systems and associated components BS EN 60529:1992+A2:2013, Degrees of protection provided by enclosures (IP code)

BS EN 60702‑1, Mineral insulated cables and their terminations with a rated voltage not exceeding 750 V — Part 1: Cables

BS EN 60896‑21, Stationary lead-acid batteries — Part 21: Valve regulated types — Methods of test BS EN 60896‑22, Stationary lead-acid batteries — Part 22: Valve regulated types — Requirements

BS ISO 8528‑5, Reciprocating internal combustion engine driven alternating current generating sets — Part 5: Generating sets IEC 60364‑5‑56, Low-voltage electrical installations — Part 5-56: Selection and erection of electrical equipment — Safety services

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