Earthing Systems

Welcome to the Schneider Electric Seminar on ‘LV Power Concepts and Devices’

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Agenda for the evening: Topic

Presenter

Time

 LV Earthing Systems

Asrar Mufti

6.15 to 6.50 pm

 LV Type Tested Panelboards

Shanker Shetty

6.50 to 7.30 pm

 Break for Salah

7.30 to 7.50 pm

 LV Power Circuit Breakers

Irfan Mufti

8.00 to 9.00 pm

 LV Final Distribution Boards

Ibrahim Saleh

9.00 to 9.30 pm

 Wiring Devices

Mohammad Al-Amoudi 9.30 to 10.00 pm

 Dinner

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10.00 pm

2

LV Earthing Systems. as per IEC 60364 Installation Standard.

Fire protection

Risk analysis - the origins of fires in buildings 

Studies carried out in Germany between 1980 and 1990 Fire 37 %

Lightning 1 %

Explosion 1 %

Cigarettes 6 %

Other 7 %

Electricity 41 %

41 % of fires are electrical in origin  this risk is far from negligible  it can be eliminated



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E92446

Accidents 7 %

Fire protection

Main cause  Ageing of the installation results in:  less effective insulation  the risk of very small leakage currents  Presence of humidity Leakage currents

Small discharges

E92462

E92461

Carbonisation of insulation (dust)

 There is a real risk of fire starting at leakage currents of 300 mA

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Basic principle

Low Voltage Earthing Systems

Zone 1 : perception Zone 2 : unpleasant sensation

T(ms)

Zone 3 : muscular contractions (reversible effects) Zone 4 : risk of ventricular

10 000 5000

fibrillation.(irreversible)

c1-c2 :prob. increases by 5% c2-c3 :prob. increases by 50% > c3

:prob. more than50 %

IEC 60479-1 Effect of current on the human body Time ms/current mA curve for AC current from 15 to 100 Hz b

c1 c2 c3

2000 1000 500

1

2

3

4

200 100 50

Body Impedance = 2000 Ohms.(Dry) = 1000 Ohms.(Wet) Max. Withstand Current = 25 mA

20 10 0,1 0,2 1 0,5 mA

2

5 10

30 mA

100

500 2000 5000 (mA) 1000

UL (MAX. TOUCH VOLTAGE) = 2000x 0.025 = 50 V (Dry Conditions) = 1000x0.025 = 25 V (Wet Conditions)

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Standard IEC 60479-1

Protection of people

Critical current thresholds

E92450

mA

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1A

Cardiac arrest

75 mA

Irreversible cardiac fibrillation

30 mA

Breathing arrest

10mA

Muscular contraction

0.5 mA

Tingling

7

Standard IEC 60479-1

Protection of people

Effect of frequency Current-sensitivity thresholds (mA) 500

100

30 50

100

1000

(f)

E92451

DC

The human body is most sensitive to frequencies in the 50 Hz/60 Hz range

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Basic principle

Low Voltage Earthing Systems

Maximum Touch Voltage Time (Protection of people according to IEC 364) Against Indirect Contact with Automatic Disconnection of Supply  Maximum touch voltage time in UL = 50 V conditions prospective touch voltage (V) < 50 50 75 90 120 150 220 280 350 500

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maximum protective device disconnection time(Seconds) AC current DC current 5 5 0.60 0.45 0.34 0.27 0.17 0.12 0.08 0.04

5 5 5 5 5 1 0.4 0.3 0.2 0.1

 Maximum touch voltage time in UL = 25 V conditions (sockets/wet areas) prospective touch voltage (V)

maximum protective device disconnection time(Seconds) AC current DC current

25 50 75 90 110 150 230 280

5 0.48 0.30 0.25 0.18 0.12 0.05 0.02

5 5 2 0.80 0.50 0.25 0.06 0.02

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Low Voltage Earthing Systems

Basic principle Protection of people, direct contact Definition  “Contact of persons or livestock with live parts which may result in electric shock”

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Low Voltage Earthing Systems

Protection of people, direct contact E36914

 Types of protection

Basic principle

Insulation Distance

IP2X or IPXXB

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TBT < 25 V

30 mA

11

Standard IEC 60364

Protection of people

Indirect contact

E92454

 “Contact of persons or livestock with exposed conductive parts in case of a fault”

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Low Voltage Earthing Systems

Basic principle Protection of people according to IEC 364

Protection against indirect contact with automatic disconnection of supply  Earthing of all the exposed conductive parts of electrical equipment and all accessible conductive parts  2 simultaneously accessible exposed conductive parts must be connected to the same earth electrode  Automatic disconnection by a protective device of the circuit in which a dangerous insulation fault occurs  The protective device must operate within a time that is compatible with "Maximum Touch Voltage & Time-Safety requirements"

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Earthing Systems - General rules according to IEC 60364 § 312.2 ■

The Three Earthing Systems 1. 2. 3.

1st letter Situation of supply T = Direct connection of Transformer Neutral with the earth I = Neutral unearthed or Impedance-earthed

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T T I

T N T

2nd letter Situation of installation frames T = Exposed frames directly earthed N = Frames connected to the supply point which is earthed, • either by a separate Protective Earth conductor (S). •Or combined with the Neutral (C)

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Earthing systems

The different types ■ explanation of symbols according to IEC 617-11 (1983) Neutral conductor (N) Protective conductor (PE) Combined protective and neutral conductor (PEN)

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Low Voltage Earthing Systems

Earthing system technique TT system E36886

Definition  The neutral point of the LV transformer is directly connected to an earth electrode

L1 L2 L3 N

Rn

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Low Voltage Earthing Systems

Earthing system technique TT system E36886

Definition  The neutral point of the LV transformer is directly connected to an earth electrode  The exposed conductive parts of the installation are connected to an electrically separate earth electrode

L1 L2 L3 N

PE Rn

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Ru

17

System earthing arrangements

Earth electrode

 "Deep" earth  the earth does not act as an insulator

 Equivalent electrical circuit  "Deep" earth is equipotential in nature…  … whatever the distance! 11 Ω 1000 km

"Deep" earth

1Ω

15 Ω

10 Ω

10 Ω

5Ω

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E92453

E92452

"Deep" earth

18

Earth electrode

System earthing arrangements

Well designed network  At A A →

IPE = 0

L1 L2 L3 N PE

→

→

→

→

→

→

I1 + I2 + I3 + IN = IPE  Well designed network

→

→

IPE = 0 →

→

→

I1 + I2 + I3 + IN = 0

 Current in the neutral  does not depend on current IPE  equal to unbalanced load currents and/or 3rd order harmonics (3 k) E92457

→

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→

IN = Iunbalance

+ I3k

→

19

Earth electrode

System earthing arrangements

Faulty distribution system

A →

IPE ≠ 0

L1 L2 L3 N PE

 Faulty distribution system → IPE ≠ 0 →

→

→

→

I1 + I2 + I3 + IN ≠ 0

→

 Current in the neutral  does not depend on current IPE  equal to unbalanced load

currents and/or 3rd order harmonics (3 k) →

IN = Iunbalance

+ I3k

→

E94409

→

 Measurement of current IPE can be used  for protection of persons (values depend on the earthing arrangement)  protection against fire hazards →  However, it is necessary to detect the "true" IPE

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TT system

System earthing arrangements

Earth-fault study Value of fault current: Uo = 230 V

L1 L2 L3 N

Id = Uo / (Rn + Ru) = 230 / (10 + 10) = 11.5 A

400 V/230 V

Ud = Ru x If Exposed conductive part

Id = 11,5 A

Ud = 115 V Load

= 115 V > UL = 50 V  The fault current generates a dangerous touch voltage  The SCPD is usually not suitable for eliminating this type of fault

Ru 10 Ω

E95420

Rn 10 Ω

= 10 x 11.5

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TT system

System earthing arrangements

Earth-fault study Uo = 230 V

400/230 V

SCPD 25 A

I∆

E95421

Rn 10 Ω

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Ru 10 Ω

L1 L2 L3 N

n = 5A

Exposed conductive part

Load

Solution  The SCPD is usually not suitable for this type of fault (ST setting at 25 A)  A residual current device specially designed for the protection of persons  Tripping conditions: Max touch voltage < Safety curve Ru x I∆ n < UL (I∆ n is the setting of RCD)  I∆ n = UL / Ru = 50 /10 =5A

22

System earthing arrangements

TT system Maximum disconnecting times Standard IEC 60364 converts the exposure-time/current curves of standard IEC 60479-1 into tables presenting the disconnecting-time versus the nominal AC-voltage (Uo) 50 V < Uo ≤ 120 V

120 V < Uo ≤ 230 V 230 V < Uo ≤ 400 V Uo >

400 V

Disconnecting time (s) AC

DC

AC

DC

AC

DC

AC

DC

TT system

5

0.2

0.4

0.07

0.2

0.04

0.1

0.3

From table 41 A of standard IEC 60364

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SEAs and devices

Earth-leakage protection  RCD technologies  electromechanical – no auxiliary power required  electronic – integrated in SCPD (no auxiliary power required)  separate from the SCPD – auxiliary supply required  RCDs are immune  to nuisance tripping  to DC currents (class A as defined by IEC 755)

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Low Voltage Earthing Systems

Associated switchgear in TT

 RCD  electromechanical – own current

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E37522

Earth leakage protection

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Low Voltage Earthing Systems

Associated switchgear in TT

 RCD  electromechanical – own current  electronic – integrated in the voltageoperated short-circuit protection device

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E37522

Earth leakage protection

26

Low Voltage Earthing Systems

Associated switchgear in TT

 RCD technologies  electromechanical – own current  electronic – integrated in the voltageoperated short-circuit protection device  separate from the short-circuit protection device – auxiliary supply

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E37522

Earth leakage protection

27

Devices for the TT system

SEAs and devices

Operating principle

Tripping

Operating principle of residual current devices requiring no auxiliary supply (electronic) Detection Measurement

No aux. power required

Detectio n

Earth-leakage relay

E37508

M

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Tripping

Measurement

28

SEAs and devices

Devices for the TT system Selection of solutions  Electromechanical technology for final distribution  Application: protection of life and property in all sectors (industrial, commercial and residential)

E37540

 Main characteristics: continuity of service and safe if neutral conductor is cut

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SEAs and devices

Devices for the TT system Selection of solutions  Electronic technology for power distribution  Application: general protection from the main low voltage switchboard to the secondary switchboard in industrial and large commercial buildings

E37541

 Main characteristics:  high-performance solutions  wide range of settings (discrimination)  miniaturisation  solutions for complex installations  qualified personnel (lead-sealable relays)

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SEAs and devices

Devices for the TT system Earth-leakage protection  Discrimination RCD1

 vertical discrimination

– setting I∆ n1 > 2 I∆ n2 RCD2

– time-delay settings RCD1 > RCD2

E95454

Caution. For an RCD not integrated in the SCPD, RCD2 disconnecting time = tripping time + time delay

E95455

 horizontal discrimination

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Applications

SEAs and devices

Coordination of RCDs

 Discrimination rules CB1

 Two conditions:

1 2

RCD1

E94442

CB2

RCD2

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I∆ n (RCD1) > 2 I∆ n (RCD2) ∆ t (RCD1) > ∆ t (RCD2) + ∆ t (CB2) (including the disconnecting time)

 To implement condition 2, it is necessary to know the total breaking time guaranteed for the CB2 + RCD2 combination or to run tests on the combination

32

Applications

SEAs and devices

Coordination of

RCDs

 Discrimination rules CB1

 Two conditions:

2

RCD1

CB2

E94442

RCD2

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1

I∆ n (RCD1) > 2 I∆ n (RCD2) setting (RCD1) ≥ setting (RCD2) +1

Condition 2 is automatically obtained for (RCD2) +1 if RCD2 is combined with a circuit breaker/switch disconnector from the Multi 9 or Compact ranges

33

Applications

RCDs

Coordination of

RCDs

 Discrimination rules with Vigirex upstream CB1

 Two conditions: 1 I∆ n (RCD1) > 1.5 I∆ n (RCD2) 2 setting (RCD1) ≥ setting (RCD2) +1

Vigi RCD1

CB2

E94442

RCD2

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Condition 2 is automatically obtained for (RCD2) +1 if RCD2 is combined with a circuit breaker/switch disconnector from the Multi 9 or Compact ranges

34

System earthing arrangements

Main features of the TT system  Protection of persons:  fault current is dangerous  fault current is too weak to trigger the short-circuit protection devices  protection must be practically instantaneous •It is provided by a specially designed RCD device  Fire protection:  fault current is limited  "naturally" managed by RCDs for the protection of persons  Continuity of service:  ensured by discrimination between the RCDs

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Low Voltage Earthing Systems

TT Earthing System Conclusion  Fault current limited  Dangerous touch voltage  First fault tripping  Human Protection ensured.  No Risk of Fire.  Continuity of Service  simple design  use of RCDs  system easily extensible.

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TN system

System earthing arrangements

Definition

E95416

L1 L2 L3 N PE

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 The neutral point of the LV transformer is directly connected to an earth electrode  The exposed conductive parts of the installation are connected by the PE to the same earth electrode

Rn

37

TN-S system

System earthing arrangements

Definition (cont.)

E95417

L1 L2 L3 N PE

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 The PE and neutral conductor are separate

Rn

38

TN-C system

System earthing arrangements

Definition (cont.)

E95423

L1 L2 L3 PEN

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 A common conductor is used for both the PE and the neutral conductors (PEN)

Rn

39

System earthing arrangements

TN-C-S system Definition (cont.)  In this TN sub-system: L1 L2 L3 PEN

L1 L2 L3 N PE

 the upstream part is TN-C

(with PEN)  the downstream part is TN-S

(with PE and N)

E95424

Note. A TN-S system may not be used upstream of a TN-C system

Rn

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System earthing arrangements

TN system Earth-fault study  Uo = 230 V

400 V/230 V

The fault current is equal to a Ph/N shortcircuit

Exposed conductive part

Uc

E95425

Fault

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ρ =0.025 Ω -mm2/m for Cu. RPE= RPH=0.025 x 50/35 = 32.14 mΩ Id = 230/(2 x 0.3214) = 3578 A. 

Id

Rn

L1 L2 L3 N PE

Consider the PH & PE Conductor are Copper, 50 m Long with a X-section of 35 mm2. The Fault Current Id =U0/(RPE +RPH) RPE= RPH=ρ . L/S

This Fault Current will generate a Touch Voltage Uc = RPE x Id = 3578 x 0.03214 = 115 V. Since the fault current depends on the Length of the Lines, it is necessary to check that the Fault Current is more than the Protection Operating Threshold of the CB i.e Id > Ia

41

System earthing arrangements

TN system

The Value of the fault current is: Id = 0.8.Uo. SPH ρ .(1 + m).L

Earth-fault study (cont.) Uo = 230 V

400 V/230 V

L1 L2 L3 N PE

where m=Sph/Spe L=Length of the Cond. Lmax = 0.8Uo. SPH ρ .(1 + m).Ia

Id

If the length of the conductor is greater than Lmax., it is necessary to; Reduce Ia.

Exposed conductive part

Uc

E95425

Fault

Increase Spe. Install an RCD.

Rn

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TN system

System earthing arrangements

Implementation Uo = 230 V

400 V/230 V

TN-S L1 L2 L3 N PE

PE separate from the neutral Protection SN

of the neutral

= SPH

– disconnected, not protected SN

< SPH

– disconnected, protected Exposed conductive part

E95426

Load

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TN system

System earthing arrangements

Implementation (cont.) TN-C Uo = 230 V

400 V/230 V

Exposed conductive part



PEN = protective conductor and neutral conductor



Protection of the PEN SPEN = SPH the PEN must not be disconnected



The exposed conductive parts of the substation, the LV neutral and the exposed conductive parts of the loads are connected to the same earth electrode

E95427

Load

L1 L2 L3 PE N

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System earthing arrangements

TN system Maximum disconnecting times  The disconnecting time depends on the distribution-system voltage Uo

50 V < Uo ≤ 120 V

120 V < Uo ≤ 230 V 230 V < Uo ≤ 400 V Uo >

400 V

Disconnecting time (s) AC

DC

AC

DC

AC

DC

AC

DC

TN system

5

0.4

5

0.2

0.4

0.1

0.1

0.8

Drawn from table 41 A of standard IEC 60364

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Devices for the TN-S system

SEAs and devices

Protection by short-circuit protection devices  Protection:  for a given cross-section and material (e.g. copper or aluminium), the fault current Id depends on the length of the conductors

t

E95442

t < 0.4 s

I

Id

 circuit breaker protection:

setting of magnetic relay / ST

t

E95449

< 30 ms

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Im

Id

I

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Low Voltage Earthing Systems

Earthing system technique

TN system- Checking of the tripping conditions:  The max. Length of any circuit of a TN-earthed installation is

0.8.Uo.Sph ρ .(1+m).Ia L = Length of the Conductor. Sph= Cross-Sectional area of Ph. Cond. ρ = resistivity in Ohm-mmsq/metre (22.5 mohm for Cu) m = Ratio between Sph and SPE Ia = Trip Current setting for Inst. Operation of CB.  If the condition is not met  reduce the magnetic setting  install an RCD - LS (up to 250A)  Increase Cross-Sectional area of the Cond. L max =



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see pg. G20 for Tables.

47

SEAs and devices

Devices for the TN-S system Protection by short-circuit protection devices  If the conditions for correct protection are not met

Circuit breaker low setting of magnetic relay/ST or installation of a standard RCD or increase the conductor cross-section

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SEAs and devices

Applications Protection of property  Protection of motors (TN-S system)

R

MERLIN GERIN

E94458

M

a low insulation fault can cause a short-circuit  an RCD with a current setting between 3 and 30 A avoids this risk 

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SEAs and devices

Devices for the TN-S system Summary Earth-fault study Uo = 230 V

400 V/230 V

SCPD tripping at 160 A RCD

L1 L2 L3 N PE

 The fault current is equal to a phase/neutral short-circuit  The fault current generates a dangerous touch voltage  The circuit breaker trips  Check the loop impedance

Exposed conductive part

 Earth-leakage protection set to 300 mA is recommended if there is a risk of fire

E95428

Load Rn

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Devices for the TN-S system

SEAs and devices

Protection by short-circuit protection devices (SCPD)  Discrimination by circuit breakers  current LT and ST settings

t D1

D2

E95450

∆1

Im1

I

Im2

 time

t D1

D2

intentional delay of the LT and ST upstream protection

E95451

∆ t

I

 energy

t D1

D2

comparison of energies (ST)

E95452

∆ I2 t

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I

51

SEAs and devices

Devices for the TN-S system Protection by short-circuit protection devices (SCPD)

 Merlin Gerin type ranges

TN-C / 3P 3D

TN-S / 4P 3D, 4P 4D

Masterpact

 circuit breakers

Compact

Multi 9 Circuit breakers also provide overload protection for all low-voltage system earthing arrangements

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SEAs and devices

Main features TN-S system

E37542

 Protection of persons:  fault current is dangerous  fault current is usually high enough to trip the SCPDs  tripping must be practically instantaneous It is ensured by the magnetic settings on the SCPDs  if the fault current is not high enough, RCDs may be used to ensure protection  Fire protection:  fault current is high  it must be managed by additional RCDs  Continuity of service:  ensured by discrimination between the short-circuit protection devices and among RCDs Division - Name - Date - Language

53

SEAs and devices

Main features TN-C

E37544

 Protection of persons:  fault current is dangerous  fault current is usually high enough to be tripped by the SCPDs  tripping must be practically instantaneous = same as TN-S It is ensured by the magnetic settings on the SCPDs  if the fault current is not high enough, the installation must be resized  Fire protection:  cannot be provided (TN-C not allowed where there is a risk of fire)  Continuity of service:  ensured by discrimination between the SCPDs = same as TN-S

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System earthing arrangements

TN system Conclusion  High fault currents  Dangerous touch voltage

Tripping after first fault  cost savings  check on tripping conditions  calculations required for extensions



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IT system

System earthing arrangements

Definition

 The exposed conductive parts of the loads are connected by the PE conductor to a common earth electrode

E95429

L1 L2 L3 N PE

 The Neutral point of the LV transformer is Isolated, not connected to an earth electrode

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IT system

System earthing arrangements

Definition (cont.)

L1 L2 L3 N PE

 The exposed conductive parts of the loads are connected by the PE conductor to a common earth electrode or to separate earth electrodes

PE

E95430

PE

 The Neutral point of the LV transformer is Isolated and not connected to an earth electrode

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System earthing arrangements

IT system Earth-fault study

L1 L2 L3

 Under Normal operation, the System is earthed by its System Leakage Impedance.

E95431

PE

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System earthing arrangements

IT system Earth-fault study (cont.)  System leakage impedance L1 L2 L3 PE

 If=U/Zt =230/3500 =0.065 A Uc=10 x0.065= 0.6V Uc< UL(50V)  The touch voltage is not

dangerous  There is no risk of fire

E95432

 The fault does not cause tripping but it must be indicated

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System earthing arrangements

IT system Signalling the first fault  Detection principle:  emission of a specific zero

sequence signal

E95433

L1 L2 L3 PE

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60

System earthing arrangements

IT system Signalling the first fault (cont.)

 Fault-clearance principle:  detection by toroid and indication of the faulty outgoer

E95434

L1 L2 L3 PE

 Detection principle:  emission of a specific zero sequence signal

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Devices for the IT system

SEAs and devices

IMD 1st fault I inj

L1 L2 L3 N PE

I inj I inj

RI

I inj

 Principle  injection of current  tracking generator  measurement of IR  IMD:(Insulation Monitoring Device)  DC current: direct measurement of IR  AC current: calculation of IR

e I inj

E95435

(IR) Insulation Resistance

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SEAs and devices

Devices for the IT system IMD 1st fault (cont.) L1 L2 L3 N

 Principle of the FTD (*)  detection of fault current  Type of FTD (*):  portable  fixed

E95436

PE

(*) Fault Tracking Device

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SEAs and devices

Devices for the IT system IMD & FTD  Merlin Gerin range  IMD (*)

 FTD (**)

(*) Insulation Monitoring Device (**) Fault Tracking Device

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SEAs and devices

Devices for first fault RCDs  Typical leakage currents following a first fault System leakage capacitance (µF) First-fault current

I∆ n setting

1

70 mA

300 mA

5

360 mA

1A

30

2.17 A

5A

 Standardised rule IEC 60364-5-53: The RCD current settings must be greater than twice the first-fault current

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Protection plan for second fault

SEAs and devices

IT system with interconnected exposed conductive parts (ECP) Study of the 2nd earth fault L1 L2 L3 N PE Id1

Id2

 The SCPD protection trips  protection is ensured by the same circuit breaker as for TN-S, mais – 4P 4t is compulsory  Check the loop impedance

E95437

Merlin Gerin circuit breakers are appropriate for protection in IT systems

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66

SEAs and devices

Devices for second fault IT system with ECPs not interconnected Study of 2nd earth fault L1 L2 L3 N

 Same principle as TT system (length of conductors)  Protection provided by RCDs (same switchgear as TT)

E95438

CPI

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SEAs and devices

Protection plan for second fault IT system Maximum disconnecting times for IT systems for the 2nd fault 50 V < Uo ≤ 120 V

120 V < Uo ≤ 230 V 230 V < Uo ≤ 400 V Uo >

400 V

Disconnecting time (s) AC

DC

AC

DC

AC

DC

AC

DC

IT system

5

0.4

5

0.2

0.4

0.1

0.1

0.8

Drawn from table 41 A of standard IEC 60364

Division - Name - Date - Language

68

SEAs and devices

Main characteristics of the IT system  Protection of persons:  the insulation fault is not dangerous

•Protection is ensured by the IT system itself, however a maintenance strategy is required A second fault is dangerous and protection must be ensured by the magnetic setting of the SCPD ’s or the RCDs  Fire protection: the fault current is close to zero  Continuity of service is total

Division - Name - Date - Language

69

System earthing arrangements

IT system Conclusion  First-fault current is very weak  First-fault touch voltage is very weak  Dangerous touch voltage in the event of a double fault  Tripping after the second fault  Optimal safety when first fault occurs  Continuity of service when first fault occurs  Use of IMD for fault tracking  Check on tripping conditions  Calculations necessary for extensions

Division - Name - Date - Language

70

Low Voltage Earthing Systems

Earthing system technique IT system Conclusion  First fault current very weak  First fault touch voltage very weak  Dangerous touch voltage if there is a double fault  Second fault tripping  optimal safety when first fault occurs  continuity of service when first fault occurs  use of PIM for fault tracking  checking of tripping conditions  calculations necessary for extensions

Division - Name - Date - Language

71

Fire protection

Standard IEC 60364  

IE C 603 64  E94550

 

Standard IEC 60364, section 3-32, defines premises presenting a risk of fire (BE2) or explosion (BE3) Standard IEC 60364, section 4-48, deals with premises where there is a risk of fire imposes use of a 500 mA RCD device recommends use of a TT or IT system for the electrical installation on such premises prohibits use of a TN-C system

In TT, IT and TN-S systems, a 300 mA RCD eliminates the risk of fire

Division - Name - Date - Language

72

Selection of a system earthing arrangement 6 selection criteria  Protection of persons  Protection of equipment  Continuity of the power supply  Effects of disturbances  Easy implementation  Economic analysis

Division - Name - Date - Language

73

System earthing arrangements

Selection of a system earthing arrangement Conclusion  Facility managers need a dependable electrical distribution  IEC 364 offers solutions which:

E37521

 optimally protect persons (systems, RCDs, neutral switching, etc.)  minimise the risk of fire (TT, IT systems, RCDs)  protect property by limiting leakage/fault currents (IT, TT, TN-S with

RCDs)  Mixing of system earthing arrangements is the means to provide optimum solutions to the needs of operators

IEC 364 means a dependable, high-performance installation

Division - Name - Date - Language

74

Low Voltage Earthling Systems

E00000

Earthing Systems Comparison.

Criterion

TT

TN-S

TN-C

IT

Protection of people

XXXX

XXX

XX

XXXX

Protection against Fire

XXXX

XXX

X

XX

Ease of Implementation Continuity of service

XXX XX

X XX

X XX

X XXXX

Upgradable installation

XXXX

XX

XX

XX

Cost Saving

XX

XXX

XXXX

X

XXXX=Excellent

Division - Name - Date - Language

XXX=Good

XX=Average

X=Caution

75