Lec 14 - Branch Circuits

Wilbert Rey D. Tarnate Instructor

1

LOAD SIDE

SOURCE SIDE

service entrance

Main Distribution Panel

feeders

Lighting Panelboard

Distribution Panel sub-feeders

sub-feeders

Distribution Panel

Panelboard

Lighting Panelboard

branch circuits branch circuits

branch circuits

branch circuits This diagram is a single-line diagram used for power flow analysis

Design Flow

LOAD SIDE

SOURCE SIDE service entrance

Main Distribution Panel

feeders

Lighting Panelboard

Distribution Panel

sub-feeders

sub-feeders Distribution Panel branch circuits

Panelboard

Lighting Panelboard

branch circuits branch circuits

branch circuits

•Loads

2 •Outlets •Switches

1

•Service

6

4

•Branch Circuits

•Panel Boards

3

7 •Conduits •Other Devices

•Feeders

5

•Grounding

8

4

•Loads

1

•Service

6

2

4

• Branch Circuits

•Outlets •Switches

•Panel Boards

3

7 •Conduits •Other Devices

•Feeders

5

•Grounding

8

5

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  

 

Define branch circuits Identify the conductors in a branch circuit Select overcurrent protection for a branch circuit Understand why branch circuits are used Select type and size of conductors for a branch circuit Distribute loads among branch circuits

6

   

 

Define branch circuits Identify the conductors in a branch circuit Select overcorrect protection for a branch circuit Understand why branch circuits are used Select type and size of conductors for a branch circuit Distribute loads among branch circuits

7

SOURCE SIDE L N

Overcurrent Device

G

8

SOURCE SIDE L N

Overcurrent Device

G

BRANCH CIRCUIT “A branch circuit is any segment of a wiring system extending beyond the final automatic overcurrent protective device that is approved for use as branch circuit protection.”

Automatic – does not need human intervention to act

9

SOURCE SIDE L N

Overcurrent Device

G

BRANCH CIRCUIT RATING “A branch circuit is rated according to the setting or rating of the overcurrent device used to protect the circuit.” Rating - the smallest current where the protective device will respond

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

  

 

Define branch circuits Identify the conductors in a branch circuit Select overcorrect protection for a branch circuit Understand why branch circuits are used Select type and size of conductors for a branch circuit Distribute loads among branch circuits

12

SOURCE SIDE L N

Overcurrent Device

G

IDENTIFICATION OF CONDUCTORS Neutral/Grounded Conductor (N) – White, gray, or any color except green with three white stripes Grounding Conductor (G) – (not part of a branch circuit) Bare, green, or green with yellow stripes Ungrounded Conductor (L) – Any other color, usually red, black, or blue

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

 

 

Define branch circuits Identify the conductors in a branch circuit Select overcurrent protection for a branch circuit Understand why branch circuits are used Select type and size of conductors for a branch circuit Distribute loads among branch circuits

14

SOURCE SIDE L N

Overcurrent Device

G

OVERCURRENT PROTECTION FUSE

I If I ≥ fuse rating, fuse filament melts. Fuse must be replaced afterwards.

15

SOURCE SIDE L N

Overcurrent Device

G

OVERCURRENT PROTECTION CIRCUIT BREAKER (CB) I If I ≥ CB rating, CB opens the circuit. CBs can also be used to manually open or close the circuit.

16

SOURCE SIDE L N

Overcurrent Device

G

OVERCURRENT PROTECTION RATING ≤ CURRENT-CARRYING CAPACITY OF BRANCH CIRCUIT CONDUCTORS 1. Readily accessible – can be reached without aid of ladders and tools and without overcoming obstacles 2. Required for each ungrounded conductor. 3. Prohibited in neutral conductors except when it opens the ungrounded and neutral conductors simultaneously.

17

SOURCE SIDE L N

Overcurrent Device

✗

G

OVERCURRENT PROTECTION RATING ≤ CURRENT-CARRYING CAPACITY OF BRANCH CIRCUIT CONDUCTORS 1. Readily accessible – can be reached without aid of ladders and tools and without overcoming obstacles 2. Required for each ungrounded conductor. 3. Prohibited in neutral conductors except when it opens the ungrounded and neutral conductors simultaneously.

18

SOURCE SIDE L

✔

N

G

OVERCURRENT PROTECTION RATING ≤ CURRENT-CARRYING CAPACITY OF BRANCH CIRCUIT CONDUCTORS 1. Readily accessible – can be reached without aid of ladders and tools and without overcoming obstacles 2. Required for each ungrounded conductor. 3. Prohibited in neutral conductors except when it opens the ungrounded and neutral conductors simultaneously.

19

SOURCE SIDE L

✗

N

G

OVERCURRENT PROTECTION RATING ≤ CURRENT-CARRYING CAPACITY OF BRANCH CIRCUIT CONDUCTORS 1. Readily accessible – can be reached without aid of ladders and tools and without overcoming obstacles 2. Required for each ungrounded conductor. 3. Prohibited in neutral conductors except when it opens the ungrounded and neutral conductors simultaneously.

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SOURCE SIDE L

✗

N

G

OVERCURRENT PROTECTION RATING ≤ CURRENT-CARRYING CAPACITY OF BRANCH CIRCUIT CONDUCTORS 1. Readily accessible – can be reached without aid of ladders and tools and without overcoming obstacles 2. Required for each ungrounded conductor. 3. Prohibited in neutral conductors except when it opens the ungrounded and neutral conductors simultaneously.

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SOURCE SIDE L

✔

N

G

OVERCURRENT PROTECTION RATING ≤ CURRENT-CARRYING CAPACITY OF BRANCH CIRCUIT CONDUCTORS 1. Readily accessible – can be reached without aid of ladders and tools and without overcoming obstacles 2. Required for each ungrounded conductor. 3. Prohibited in neutral conductors except when it opens the ungrounded and neutral conductors simultaneously.

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SOURCE SIDE L

✗

N

G

OVERCURRENT PROTECTION RATING ≤ CURRENT-CARRYING CAPACITY OF BRANCH CIRCUIT CONDUCTORS 1. Readily accessible – can be reached without aid of ladders and tools and without overcoming obstacles 2. Required for each ungrounded conductor. 3. Prohibited in neutral conductors except when it opens the ungrounded and neutral conductors simultaneously.

23

SOURCE SIDE L

✔

N

G

OVERCURRENT PROTECTION RATING ≤ CURRENT-CARRYING CAPACITY OF BRANCH CIRCUIT CONDUCTORS 1. Readily accessible – can be reached without aid of ladders and tools and without overcoming obstacles 2. Required for each ungrounded conductor. 3. Prohibited in neutral conductors except when it opens the ungrounded and neutral conductors simultaneously.

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VI. Branch Circuit Overcurrent Protection 1. General Rule - The rating or setting of an overcurrent device in any branch circuit must not exceed the current-carrying capacity of the circuit conductors.

2. Specific Rules 1. 2.

3.

4.

5.

An overcurrent device must be placed at the supply end of each ungrounded conductor of the circuit to be protected. An overcurrent device must not be placed in a permanently-grounded conductor, except where the device simultaneously opens all conductors of the circuit.

Where the device protecting a conductor has a rating or setting that also provides protection for smaller conductors, there is no need to provide protection at the point where the smaller conductors are tapped from the larger conductor. Non-motor-operated appliance branch circuit protective devices shall not exceed 150% of the appliance rating. Overcurrent devices must be located such that they are readily accessible.

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 

  

Define branch circuits Identify the conductors in a branch circuit Select overcorrect protection for a branch circuit Understand why branch circuits are used Select type and size of conductors for a branch circuit Distribute loads among branch circuits

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Subfeeder

Branch Circuits

Why distribute loads among branch circuits? Reliability Diff. load requirements Standardization Reduction of wire size

Panel Board –

contains devices for overcurrent protection

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Type of BC

Individual - serving one outlet

Allowable BC Rating (A)

Any

Permissible Loads Any

General-purpose lighting load

15 or 20

Rating of any one Cord-and-plug attached equipment ≤ 0.8 (BC Rating) If supplying other loads, total rating of equipment fastened in place (not including luminaires) ≤ 0.5 (BC Rating)

Multioutlet - Serving multiple outlets

Luminaires with heavy-duty lamp holders not in dwelling units

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40 or 50

Cord-and-plug attached equipment ≤ 0.8 (BC Rating)

Cooking appliances fastened in place. Luminaires with heavy-duty lamp holders not in dwelling units, infrared heating units, etc.

>50

Non-lighting outlets 29



  





Define branch circuits Identify the conductors in a branch circuit Select overcorrect protection for a branch circuit Understand why branch circuits are used Select type and size of conductors for a branch circuit Distribute loads among branch circuits

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Maximum load of Branch Circuits

Non-continuous load + 1.25 (Continuous load) ≤ BC Rating * Continuous load – maximum current (RMS) is expected to continue for 3 hrs.

Maximum Rating of Individual BC

If appliance is non-motor operated: BC rating ≤ 1.5 (appliance rating)

Selection of Conductors General Rule: Branch circuit conductors shall have an ampacity of not less than the rating of the branch circuit and not less than the load to be served. Ampacity – current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Conditions: Ambient temp. Neighboring conductors

Surrounding materials

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Selection of Conductors 







The type of insulation of conductors must be suited to the desired operation.

Where ambient temperature exceeds 30°C, the ampacities of the conductors shall be derated according to correction factors given at the bottom of each of the ampacity tables (Tables 3.10.1.16 to 3.10.1.21). Where more than three (3) conductors are used in a raceway or cable, the conductor ampacities must be derated from the ampacity values to compensate for increased heating due to reduced ventilation of an enclosed group of closely-spaced conductors (see Note No.8). A 1% to 2% voltage drop is recommended for branch circuit conductors.

Table 3.10.1.6 Allowable Ampacities of Insulated Conductors Rated 0 - 2000 Volts, 60º to 90º C Not More Then Three Conductors in Raceway or Cable or Earth (Directly Based), Based on Ambient Temperature of 30º C Size

Temperature Rating of Conductor. See Table 3.10.1.13 Size 60º C 75º C 85º C 90º C 60º C 75º C 85º C 90º C Types Types Types Types Types Types Types Types RUW, FEPW, V, TA, RUW, RH, V, TA, T, RH, MI TBS, T, RHW, MI TBS, TW, RHW, SA, TW, RUH, SA, 2 mm UF RUH, AVB, UF THW, AVB, mm2 (mm. dia.) THW, SIS, THWN, SIS, (mm. dia.) THWN, †FEP, XHHW, †RHH, XHHW, †FEPB, USE †THHN, USE, †RHH, †XHHW* ZW †THHN, †XHHW*

COPPER 2.0(1.6) 3.5(2.0) 5.5(2.6) 8.0(3.2) 14 22 30 38 50 60 80 100 125 150 200 250 325 400 500

15 20 30 40 55 70 90 100 120 135 160 185 210 240 280 315 370 405 445

15 20 30 45 65 85 110 125 145 160 195 220 255 280 330 375 435 485 540

25 30 40 50 70 90 115 130 150 170 205 225 265 295 355 400 470 515 580

25 30 40 50 70 90 115 130 150 170 205 225 265 295 355 400 470 515 580

ALUMINUM OR COPPERCLAD ALUMINUM …. …. …. …. 15 15 25 25 25 25 30 30 30 40 40 40 40 50 55 55 55 65 70 70 70 85 90 90 80 95 100 100 95 115 120 120 105 125 135 135 125 150 160 160 145 170 180 180 170 200 210 210 190 230 240 240 225 270 290 290 260 305 330 330 295 355 380 380 330 395 420 420 370 440 475 475

…. 3.5(2.0) 5.5(2.6) 8.0(3.2) 14 22 30 38 50 60 80 100 125 150 200 250 325 400 500

Size

mm2 (mm. dia.)

60º C Types RUW, T, TW, UF

Temperature Rating of Conductor. See Table 3.10.1.13 75º C 85º C 90º C 60º C 75º C 85º C 90º C Types Types Types Types Types Types Types FEPW, V, TA, RUW, RH, V, TA, RH, MI TBS, T, RHW, MI TBS, RHW, SA, TW, RUH, SA, RUH, AVB, UF THW, AVB, THW, SIS, THWN, SIS, THWN, †FEP, XHHW, †RHH, XHHW, †FEPB, USE †THHN, USE, †RHH, †XHHW* ZW †THHN, †XHHW* ALUMINUM OR COPPER-CLAD COPPER ALUMINUM CORRECTION FACTORS

Size

mm2 (mm. dia.)

Ambient For ambient temperature over 30º C, multiply the ampacities Ambient Temp. ºC shown above by the appropriate correction factor to determine Temp. ºC 31-40 0.82 0.88 0.90 0.91 0.82 0.88 0.90 0.91 31-40 41-50 0.58 0.75 0.80 0.82 0.58 0.75 0.80 0.82 41-50 51-60 …. 0.58 0.67 0.71 …. 0.58 0.67 0.71 51-60 61-70 …. 0.35 0.52 0.58 …. 0.35 0.52 0.58 61-70 71-80 …. …. 0.30 0.41 …. …. 0.30 0.41 71-80 † The load current rating and the overcurrent protection for these conductors shall not exceed 15 amperes for 2 mm2 (1.6 mm. dia.) 20 amperes for 3.5 mm2 (2.0 mm. dia.), and 30 amperes for 5.5 mm2 (2.6 mm. dia.) copper; or 15 amperes for 3.5 mm2 (2.0 mm. dia.) and 25 amperes for 5.5 mm2 (2.6 mm. dia.) aluminum and copper-clad aluminum.

* For dry locations only. See 75º C column for wet locations.

Table 3.10.1.17 Allowable Ampacities of Insulated Conductors Rated 0 - 2000 Volts, 60º to 90º C Single Conductor in Free Air, Based on Ambient Temperature of 30º C Size

Temperature Rating of Conductor. See Table 3.10.1.3 Size 60º C 75º C 85º C 90º C 60º C 75º C 85º C 90º C Types Types Types Types Types Types Types Types RUW, FEPW, V, TA, RUW, RH, V, TA, T, RH, MI TBS, T, RHW, MI TBS, TW RHW, SA, TW, RUH, SA, mm2 RUH, AVB, THW, AVB, mm2 (mm. dia.) THW, SIS, THWN, SIS, (mm. dia.) THWN, †FEP, XHHW †RHH, XHHW, †FEPB, †THHN, ZW †RHH, †XHHW* †THHN, †XHHW*

COPPER 2.0(1.6) 3.5(2.0) 5.5(2.6) 8.0(3.2) 14 22 30 38 50 60 80 100 125 150 200 250 325 400 500

20 30 40 55 80 105 130 155 180 205 250 290 335 375 440 505 600 675 770

20 30 45 60 95 130 160 185 220 250 300 355 400 440 540 620 720 810 930

30 40 55 70 105 140 170 195 235 260 320 370 420 475 570 655 770 875 995

30 40 55 70 105 140 170 195 235 260 320 370 420 475 570 655 770 875 995

ALUMINUM OR COPPERCLAD ALUMINUM …. …. …. …. 20 20 30 30 30 30 45 45 45 50 55 55 60 75 80 80 80 100 110 110 100 125 130 130 120 145 155 155 145 170 180 180 160 195 205 205 195 230 245 245 220 270 285 285 260 310 325 325 290 350 370 370 350 420 445 445 400 480 510 510 475 570 610 610 535 645 695 695 620 745 795 795

…. 3.5(2.0) 5.5(2.6) 8.0(3.2) 14 22 30 38 50 60 80 100 125 150 200 250 325 400 500

Size

Temperature Rating of Conductor. See Table 3.10.1.17 60º C Types RUW, T, TW

mm2 (mm. dia.)

75º C Types FEPW, RH, RHW, RUH, THW, THWN, XHHW, ZW

85º C Types V, MI

90º C Types TA, TBS, SA, AVB, SIS, †FEP, †FEPB, †RHH, †THHN, †XHHW*

60º C Types RUW, T, TW,

75º C Types RH, RHW, RUH, THW, THWN, XHHW

85º C Types V, MI

90º C Types TA, TBS, SA, AVB, SIS, †RHH, †THHN, †XHHW*

Size

mm2 (mm. dia.)

ALUMINUM OR COPPER-CLAD ALUMINUM CORRECTION FACTORS

COPPER

Ambient For ambient temperature over 30º C, multiply the ampacities Ambient Temp. ºC shown above by the appropriate correction factor to determine Temp. ºC 31-40 0.82 0.88 0.90 0.91 0.82 0.88 0.90 0.91 31-40 41-50 0.58 0.75 0.80 0.82 0.58 0.75 0.80 0.82 41-50 51-60 …. 0.58 0.67 0.71 …. 0.58 0.67 0.71 51-60 61-70 …. 0.35 0.52 0.58 …. 0.35 0.52 0.58 61-70 71-80 …. …. 0.30 0.41 …. …. 0.30 0.41 71-80 † The load current rating and the overcurrent protection for these conductors shall not exceed 20 amperes for 2 mm2 (1.6 mm. dia.), 25 amperes for 3.5 mm2 (2.0 mm. dia.), and 40 amperes for 5.5 mm2 (2.6 mm. dia.) copper; or 20 amperes for 3.5 mm2 (2.0 mm. dia.) and 30 amperes for 5.5 mm2 (2.6 mm. dia.) aluminum and copperclad aluminum.

Notes to tables 3.10.1.6 through 3.10.1.13 8. More than 3 Conductors in a raceway or cable. Where the number of conductors In

a raceway or cable exceed 3, the maximum allowable load current of each conductor shall be reduced as shown in the following table Number of Conductors

Percent of Values in Tables 5.3.2.4 and 5.3.2.6

4 thru 6

80

7 thru 24

70

25 thru 42

60

43 and above

50

Where single conductors of multi-conductor cables are stacked or bundled without maintaining spacing and are not installed in raceways, the maximum allowable load current of each conductor shall be reduced as shown in the above table.

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Exceptions a. When conductors of different systems, as provided in Section 3.0.1.3, are installed in a common raceway, the derating factors shown above shall apply to the number of power and lighting conductors only (Articles 2.10, 2.15, 2.20 and 2.30). b. The derating factors of Sections 3.1.2.4(c), 3.3.1.2(a) and 3.3.2.1(b) shall not apply when the above derating factors are also required. c. For conductors installed in cable trays, the provisions of Section 3.18.1.11 shall apply.

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In dwelling units, at least one (1) ◦ 20-A Small-appliance BC(one per kitchen) ◦ 20-A Bathroom BC (for equipment in bathroom) ◦ 20-A Laundry BC

 For a dwelling unit not more 50sqm., it shall be permitted

to have only one 20-A BC provided that the total load shall not exceed 3680 VA.

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Small-Appliance BC (kitchen, pantry, etc.) May include: receptacle outlets, countertops, and refrigerator no other except outlets for clock and a supplementary equipment

Laundry BC other outlets not for laundry may not be included

Bathroom BC outlets not in the bathroom may not be included

Individual BC Other BC

depending on the BC rating allowed for specific loads; designers’ way & the rules of thumb

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Step 1: List down groups of similar branch circuits and their ratings. ◦ E.g. lighting bc, receptacle bc, small-appliance bc, individual bc

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Step 2: Do load calculation for each group Step 3: Determine the number of branch circuits per group based on the BC ratings, allowances, and the load to be served

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1.

Lighting and Receptacle Branch Circuits for General Illumination - Larger of: VA/sqm of listed occupancies (Table 2.20.1.3(a)) and actual load, if known - branch circuit rating: 15 or 20 A

Table 2.20.1.3(a) General Lighting Loads by Occupancies Type of Occupancy Armories and Auditoriums Banks Barber Shops and Beauty Parlors Churches Clubs Court Rooms *Dwelling Units Garages-Commercial (storage) Hospitals *Hotels and Motels, including apartment houses without provisions for cooking by tenants Industrial Commercial (Loft) Buildings Lodge Rooms Office Buildings Restaurants Schools Stores Warehouses (storage) ' In any of the above occupancies except one family dwelling and individual dwelling units of twofamily and of multifamily dwellings: Assembly Halls and Auditoriums Halls, Corridors, Closets, Stairways Storage Spaces

Unit Load per Sq. M. (VA/m 2) 8 28** 24 8 16 16 24 4 16 16 16 12 28** 16 24 24 2

8 4 2

Notes: * All receptacle outlets of rating 20 A or less in one-family, two-family and multifamily dwellings and guest rooms of hotels and motels except those connected to the receptacle circuits specified in Section 2.20.1.3(b) shall be considered outlets for general illumination. No additional load calculations shall be required for such outlets. … but you may. Lighting loads in 2.20.1.3(a) includes  all general-use receptacles rated 20-A or less including receptacles connected to the circuits in (2.10.1.11.c.3.) bathroom branch circuits  receptacle outlets in 2.10.3.3(e) – (g). outdoor outlets, laundry areas, basements and garages  lighting outlets in (2.10.3.21.a - b) dwelling units and guest rooms

Notes: **In addition, a unit load of 8 volt-ampere per square meter shall be included for general purpose receptacle outlets when the actual number of general purpose receptacle outlets is unknown.

2.

Heavy-duty Lamp-holders in Fixed Lighting Units Larger of: - 600 volt-amperes per unit (sec2.20.1.3(b)), or - Actual load, if known Branch Circuit Rating: 30, 40, or 50 A

3.

General Receptacles - 180 volt-amperes per receptacle (sec2.20.1.3(b)) Branch Circuit Rating: 15 or 20 A

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4.

Show Window Illumination Larger of: - 600 volt-amperes per linear meter (sec 2.20.1.3(c) except .3), or - Actual load, if known Branch Circuit Rating: depends on type of lamp-holder

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5.

6.

Specific Appliance - Ampere rating of appliance Branch Circuit Rating: depends of FLC of appliance

Small Appliance for Dwelling Unit (sec 2.20.2.7(a))

- Branch Circuit Rating: 20 A

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7.

Laundry Loads for Dwelling Unit Branch Circuit Rating: 20 A

8.

Electric Ranges and Cooking Equipment - Ampere rating of equipment Branch Circuit Rating: 40 or 50 A

9.

Motor Loads - 1.25 * Motor Full-load current specified by the code Branch Circuit Rating: Any

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10.

Motor Loads - Full load current of motor x 230 V x 125% Branch Circuit Rating: any rating

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Minimum number of Branch Circuits per Load Group

Total computed load in VA = Branch Circuit Rating

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Determine the minimum number of branch circuits required for an office building with the following lighting and receptacle loads: a. Floor area of 30 meters by 60 meters b. 400 150-W incandescent lamps c. 15 meter long show window d. Special lighting load of 100 fluorescent lighting fixtures; each unit draws 2.5 amperes e. 200 duplex receptacles Use 20-Amp Branch Circuits 56

Solution: a. General Illumination Larger of: - 30m x 60m x 28 VA/sq.m. x 1.25 = 63,000 VA, or

- 400 units x 150 VA/unit x 1.25

= 75,000 VA

No. of B.C. = ___75,000VA___ (20A) (230V) = 16.3 therefore, use 17 B.C. (min) Or 400 UNITS/17 = 23 outlets per BC (MAX)

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b. Show Window -15 m x 600 VA/m x 1.25 = 11,250 VA No. of B.C. = 11,250 = 3 B.C. 230 x 20 (minimum) c. Special Lighting Load -100 units x 2.5 A/unit x 230 V x 1.25 = 71,875 VA No. of B.C. = 71,875 = 16 B.C. 230 x 20 (minimum)

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d. General Receptacles

- 200 units x 180 VA/unit x 1.25 = 45,000 VA No. of B.C. = 36,000 x 1.25 = 10 B.C. 230 x 20 (minimum)

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Single Family Dwelling Unit: (30 deg. Celsius ambient) The dwelling has a floor area of 145 m2. It has the typical household appliances including one 8-kW electric range, two 1-Hp room airconditioning unit, one 1.5 Hp room air-conditioning unit, and one 1-Hp water pump. For this unit a. Determine the minimum number of branch circuits and the size of THW conductors to be used considering that:  20-ampere BC will be used as much as possible.  At least two 20-ampere BCs will be provided for general illumination.  Individual BCs will supply power to the range, air-conditioning units, and water pump  The unit has one kitchen with a countertop  The unit has laundry appliances.  There are no receptacle outlets in any bathroom.

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