Branch Circuit Flashcards
True or False: The rating of a branch circuit is determined by the maximum ampere rating of the overcurrent protective device and ALSO by the size of the conductors used for the branch-circuit
FALSE: The rating of a branch circuit is determined by the maximum ampere rating of the overcurrent protective device and NOT by the size of the conductors used for the branch-circuit
True or False: Branch-circuit conductors shall have an allowable ampacity of NOT less than 125% of the continuous load, plus 100% of the non-continuous load to be served.
TRUE
When a single branch-circuit serves a continuous load of 20 amperes and a non-continuous load of 10 amperes, the branch-circuit conductors are required to have an allowable current-carrying capacity of at least _______.
- 00 amperes
- 50 amperes
- 00 amperes
- 50 amperes
=35.00 amperes
20 amperes x 1.25 = 25 amperes
10 amperes x 1.00 = 10 amperes
Total. = 35 amperes
True or False: Continuous load is a load where the minimum current is expected to continue for 3 hours or more
False: Continuous load is a load where the MAXIMUM current is expected to continue for 3 hours or more
True or False: Examples of continuous loads are lighting loads for commercial and industrial occupancies that are expected to be operated for at least three (3) hours
True
Examples of non-continuous loads are ….
General Purpose receptacle outlets provided for commercial, industrial, and residential occupancies and general.
Purpose lighting loads for RESIDENTIAL occupancies
When a 100 ampere rated circuit breaker is used to protect a branch circuit serving a continuous load, the load shall not exceed
80 amperes
100 amperes
125 amperes
115 amperes
=80 amperes
100 amperes x .80 = 80 amperes
Note* Overcurrent devices protecting branch circuits, are not to be loaded more than 80% of their rated value when protecting CONTINUOUS loads.
True or False: If the overcurrent device protecting the circuit is listed for continuous operations. It shall be permitted to have a rating of 100% of the continuous load(s) to be served. Circuit breakers are NOT listed for continuous operation, unless they have a rating of at least 400 amperes and more.
True
True or False: Lighting loads are to be suppled by 20 ampere rated branch circuits
False. Lighting loads are to be suppled by 15- AND 20 ampere rated branch circuits
How are lighting loads for specific occupancies determined?
Lighting loads are based on the unit load per square foot, depending upon the table (loads per occupancy)
How are GENERAL lighting loads to be calculated?
Lighting loads are to be calculated from the outside dimensions of the building.
How do you determine the area of a building to find the lighting load?
Square Foot, multiply the length of a building times the width of the building
A building has outside dimensions of 100 feet in length and 75 feet in width. The building has a total area of
750 sqft
175 sqft
7500 sqft
1750 sqft
=7500 sqft
100ft x 75 ft = 7500 sqft
How do you determine the area of a multi-story building?
Multiply the length of the building by the width of the building *** by the number of stories
A 3 story building having outside dimensions of 100ft by 75 ft has a total area of
2225 sqft
7,500 sqft
15,000 sqft
22,500 sqft
=22,500 sqft
100ft x 75ft x 3 (stories) = 22,500 sqft
When calculating lighting loads for dwelling units, do you include open porches, garages, or unfinished spaces not adaptable for future use?
No.
When calculating lighting loads for dwelling units, do you include garages?
No.
Are lighting loads of the habitable spaces of guest rooms of hotels and motels considered continuous?
No.
Are lighting loads of commercial and industrial occupancies considered continuous?
Yes.
What is the formula used to determine the minimum number of general lighting branch circuits required for a dwelling unit?
Number of Circuits = Load VA / Circuit VA
A dwelling unit having 2,000 sqft of habitable space is required to have a least ________ 15 ampere, 120 -volt general - purpose lighting branch - circuits.
2
3
4
5
=4
2000 sqft x 3 va / 120 volts x 15 amperes
6000VA/1800VA = 3.3 (4 circuits)
A multifamily condo, without cooking facilities provided for the tenets, having 12,000 sqft of living areas is required to have at least _________ 20 ampere, 120 volt general lighting branch-circuits, or at least ______15 ampere, 120 volt general lighting branch-circuits.
10-10
14-14
10-13
10-14
=10-14
12,000sqft x 2VA / 120volts x 20 amperes
24,000 VA / 2,400 VA = 10 circuits
12,000sqft x 2VA / 120volts x 15 amperes
24,000VA/1800VA =13.3 = 14 circuits
*Multifamily dwellings without cooking are calculated the same load Hotel and Motels (2VA)
What is the formula used to determine the minimum number of required general lighting branch-circuits for an office building, store, bank, restaurant, etc?
Number of circuits = load VA x 125% / circuit VA
A 10,000 sqft restaurant is required to be provided with at least ___ 20- ampere, 120-volt general lighting branch-circuits.
8
9
10
11
=11
10,000 x 2VA x 125% / 120volts x 20 amps
25,000 VA/2,400 VA = 10.4 (11 circuits)
**Because the circuit breakers protecting the branch-circuits are not permitted to be loaded to more than 80% of their rated value, we can also use this formula…
number of circuits = load VA / circuit VA x 80%
number of circuits = 10,000 x 2VA/ 120x20x80%
= 20000VA/1920
=10.4 (11 circuits)
Many commercial, particularly mercantile, occupancies have luminaries (lighting fixtures) installed for display, speciality, enhancement lighting in addition to general lighting. Are those loads required to be included?
Yes.
When reviewing the table, you will notice subscript referring you to another table.
**This article indicates when the number of general-purpose receptacle outlets to be installed in the building has not yet be determined, one VA per square foot is to be added to the calculation for the outlets.
**The NEC initiated this requirement because it is common practice for banks and offices buildings to have future tenant spaces and the actual number of general purpose receptacle outlets to be installed have not been determined prior to complete construction of the building.
A 15,000 sqft retail store has 10,000 VA of accent lighting in addition to the general lighting. How many 120 volt, 20 ampere branch circuits are required for the accent and general lighting loads?
30
24
36
32
= 30 circuits
General Ltg. circuits = 15,000 x 3 VA / 120x20x80%
GLC = 45,000/1920
=23.4
=24
Accent Ltg. circuits = 10,000VA /120x20x80%
ALC = 10,000/1920
=5.2
=6
24+6 = 30 circuits
What is the formula used to determine the maximum number of receptacle outlets permitted on a branch circuit?
of receptacles = circuit VA / 180VA
No more than _______ duplex receptacle outlets installed in a commercial establishment may be supplied from a single 20-ampere rated, 120 volt branch circuit.
10
12
13
14
=13
120volts x 20 amperes / 180VA
2,400 VA/ 180VA
=13.3
=13 receptacles
What is the formula for determining minimum number of required branch-circuit for general purpose receptacle outlets when the specific number of receptacle outlets to be installed in a commercial building is known.
of circuits = #of receptacles x 180VA / circuit VA
You are to install 100 duplex receptacle outlets in an existing office building. How many 20 ampere, 120 volt, branch circuits will need to be added to supply the additional receptacles?
12
10
7
8
=8 =180VA x 100 / 120volts x 20 amps =18,000/2,400 =7.5 =8 circuits
A continuous load is a load where the maximum current is expected to continue for _______ or more
15 min
1 hour
2 hour
3 hours
Defintion
= 3 hours
Disregarding exceptions, branch-circuit conductors serving continuous loads are required to have an allowable ampacity of at least __________ of the load(s) to be served.
80%
100%
125%
150%
= 125%
***Chart 210.19
A six(6) story office building having outside dimensions of 100 feet by 150 feet, has a total area of ______.
10,000 sqft
15,000 sqft
90,000 sqft
60,000 sqft
= 90,000 sqft
100ft x 150ft x 6 stories = 90,000 sqft
Of the following listed, which one is NOT a standard rating for a circuit breaker?
50 amperes
75 amperes
90 amperes
110 amperes
= 75 amperes
**Table 240.4
In general, regardless of the conductor insulation, size 10 AWG copper conductors shall have overcurrent protection rated at NOT more than ________
30 amperes
25 amperes
35 amperes
20 amperes
= 30 amperes
**Table 240.4
Find Section 220.14 to calculate window lighting.
A retail department store is to have seventy five (75) continuous linear feet of show window space. Using the linear foot method of calculation, how many 20 ampere, 120 volt, branch-circuits must be provided for the how windows lighting?
8
7
6
5
=8
=200VA x 75ft. x 125% / 20amps x 120 volts
=18,750/2400
=7.8
= 8 circuits
A small cabinet makers shop is to install fifty (50) feet of multioutlet assembly where the appliances to be used are unlikely to be operated simultaneously. Where 20-ampere, 120 volt branch circuits are used to supply the assembly, what is the minimum required?
1
2
3
4
of circuits = linear ft. x 180VA / circuit VA
= one (1)
**When calculating the branch-circuits required for fixed multi-outlet assemblies where the cord-connected appliances are likely to be used simultaneously,
(50/5) x 180 / 120volts x 20 amps
=(10) x 180 / 2,400
=1800/2400
=.75 or 1 circuit
75 feet of fixed multioutlet assembly is to be wall mounted in a retail outlet displaying television sets where most of the TV sets are operating simultaneously. How many 20-ampere, 120 volt branch - circuits are needed to supply this installation?
2
5
6
7
=6
75ft x 180VA / 120volts x 20amps
=13,500/2,400
=5.6 or 6 circuits
True of False: the definition of an individual branch-circuit is a branch-circuit that supplies only one utilization equipment.
True - examples being electric water heaters, dryer, ranges, cooktops, air conditioner, etc.
What table # gives the standard size ampere ratings of fuses and circuit breakers
240.6
True or False: Fixed storage-type water heaters with a capacity of 120 gallons or less shall be considered a non-continuous load when sizing branch-circuits.
False. water heaters are considered a CONTINUOUS load.
The branch-circuit conductors supplying a 5 kw, 240 volt, single phase water heater, are required to have an ampacity of at least
- 0 amperes
- 8 amperes
- 0 amperes
- 2 amperes
=26.0 amperes
I = 5kWx1000 / 240volts
I= 5000/240
= 20.8 x 125%
=26.04
*To solve this problem you should refer to 422.13 and 422.10 (appliances tab)
The MAXIMUM size circuit breaker that may be used to protect 5 kW, 240 volt, single phase electric water heater has a rating of ______
20 amperes
25 amperes
30 amperes
35 amperes
=35 amperes
I = 5000/240
= 20.8 amps x 150% = 31.2 amperes
**the next standard size circuit breaker has a rating of 35 amperes. To solve this problem you should refer to 422.13 and 240.6
The branch-circuit conductors supplying a 15 kW, 240 volt, single-phase fixed electric space heater, are required to have an ampacity of at least ______
42 amperes
52 amperes
63 amperes
78 ampere
=78 amperes
I = 15 x 1,000/240
I = 15000/240
=62.5 x 125%
=78 amperes
of circuits = load VA x 125%/circuit VA
The minimum number of 120 volt, 15 ampere, general lighting branch circuit required with a dwelling 70ft by 30ft of livable space is _________
2
3
4
5
=4
70ftx30ft = 2,100sqft x 3 VA = 6,300 VA
# of circuits = 6,300VA/ 120volts x 15 amp =3.5 (4 circuits)
When calculating the minimum number of required branch circuits for general purpose receptacles in a dwelling, how many VA per sqft is to be used for the calculation?
None
1 VA
2 VA
3 VA
=NONE
Table 220.14
For other than dwelling units, receptacle outlets are to be calculated at the value of NOT less than ______ for each single or duplex receptacle.
100 VA
120 VA
150 VA
180 VA
=180 VA
Table 220.14
What is the MAXIMUM continuous load, in VA, that a 240 volt, single phase, branch circuit may be protected with a 20 ampere rated circuit breaker?
2,400 VA
2,850 VA
3,840 VA
4,800 VA
3,840 VA
=240volts x 20 amperes x 80% = 3,840
Table 210.20
Determine the MINIMUM number of 15-ampere, 120 volt general lighting branch circuits required for a dwelling having 2600 sqft of habitable space, a garage that measures 20ft by 30ft and 1300sqft basement that is adaptable for future use.
8
7
6
5
= 7
2600sqft + 1300sqft = 3900sqft
=3900sqft x 3VA / 120 volts x 15 amperes
=11,700 VA (load) / 1,800 circuit
=6.5 (7 curcuits)
A 240-volt, single phase, 3,600 watt electric water heater is to be installed in a residential garage. What is the MAXIMUM size circuit breaker permitted for overcurrent protection for the water heater?
15
20
30
25
Current Formula Table, 240.6
=25
I = 3,600 VA / 240 volts = 15 amps x 150%
=22.5 amperes
*Note= the NEXT size circuit breaker has a rating of 25 amperes
A multifamily apartment complex, with cooking facilities provided for the tenants, having 16,000 sqft of living areas, is required to have a LEAST _________ 20 ampere, 120 volt general lighting branch-circuits
18
27
20
14
Table 220.12
=20
=16,000 sqft x 3VA / 120volts x 20 amps
=48,000 VA(load)/ 2,400 VA (circuit)
=20 circuits
*Note =Apartments WITH cooking facilities are considered dwelling units.
A 6,000 sqft bank is required to be provided with at LEAST ______ 20-ampere, 120-volt general lighting branch-circuits.
8
9
10
11
Table 220.12, 210.19
=11
=6,000 x 3.5VA x 125% / 120volts x amps
=26,250VA (load) / 2,400 VA (circuit)
=10.9
=11 circuits
For a retail store, determine the MAXIMUM number of 120 volt fluorescent luminaries(lighting fixtures), each drawing 1.6 amperes, may be suppied from a 20-amepere rated, 120 volt lighting branch-circuit
10
8
13
9
Table 220.18, 210.20
=10
= 120volts x 20amps x 80% /120 volts x 1.6 amps
= 1,920 VA (circuit) / 192 VA (fixture)
= 10 luminaires
For a commercial building, NO more than ______ single or duplex receptacles may be supplied from a 15 ampere, 120 volt branch circuit.
10
11
12
13
Table 220.14
=10
= 120volts x 15 amps/ 180VA
=1800VA (circuit) /180 VA (recpt.)
=10 receptacles
200ft of fixed multi-outlet assembly is to be wall mounted in a computer classroom where most of the computers are to be operating simultaneously. Determine the MINIMUM number of 20 ampere, 120volt branch circuits required to supply the multi-outlet assembly.
12
15
13
11
Table 220.14
=15
=200ft x 180VA / 120volts x 20 amps
=36,000 VA (load) / 2,400 VA (circuit)
=15
The branch-circuit conductors supplying a 30 gallon fixed storage type water heater, are required to have an ampacity of at LEAST _____ of the marked nameplate rating of the appliance.
80%
100%
125%
150%
=125%
Table 422.13
Given: You are to install 100, 277volt fluorescent luminaries (lighting fixtures) in a tenant space of a retail outlet mall. The lighting fixtures have a current rating of .75 amperes each. Determine the MINIMUM number of 20 ampere, 277 volt branch-circuits required to supply the luminaries.
4
7
6
5
=5
= 100x227Vx.75A / 277V x 20A x 80%
= 20,775 VA (load)/ 4,432 VA (circuit)
=4.6 or 5 circuits
Table 220.18
A branch-circuit is to supply a continuous load of 160 amperes. The branch circuit conductors are required to have an ampacity (current-carrying capacity) of at LEAST ______.
160 amperes
200 amperes
150 amperes
128 amperes
=200 amperes
160 amps x 125% = 200 amperes
Table 210.19
The MAXIMUM ampere rating for a circuit breaker protecting a residential central space electric heating unit rated 18kW at 240volts, single phase is _______.
75 amperes
80 amperes
90 amperes
100 amperes
Current Formula, Table 424, Table 210, Table 240
= 100 amperes
I = 18 x 1,000/240 volts
I = 18,000/240
=75 amps x 125%
=93.73 amperes
**Note - the NEXT standard size circuit breaker has a rating of 100 amperes
