NEC Code Questions Practice Test-9
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Free Online Practice Quiz NEC Code Questions-9
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Question 1 of 10
1. Question
what size of conductor must be used to protect against over current for a continuous load of 22 amperes at 750C?
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The size of branch circuit conductor to protect against over current must be more than 125 % of continuous load.
22 * 1.25 = 27.5 amperes.
Refer : Table 310.15(B)(16).
No 10 THWN with 35 amperes at 75 0C is suitable -
Question 2 of 10
2. Question
What size of feeder conductors are required for a dwelling unit which has a calculated load of 240 A. The service disconnect is rated for 250 A and feeder conductors carry entire load of the dwelling unit?
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Answer: 4/0 AWG
Note: Feeder conductors that supply entire load of dwelling unit can have the rating of 83% of service disconnect of dwelling unit.
The service conductor ampacity for 250 A service disconnect = 0.83 * 250 = 207.5 amperes
Refer : NEC Table 310.15(B)(16)
4/0 AWG with ampacity 250 amperes ( 75 C) is suitable as service conductor
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Question 3 of 10
3. Question
What size branch circuit conductor is required for a 4000 W, 240 electric water heater?
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Branch circuit conductor size should 125% of continuous load [ NEC 422.10(A)]
Electric water heater current = 4000 / 240 = 16.6 Amperes
Branch conductor size = 16.6 * 1.25 = 20.75 amperes
As per branch conductor next size up rule
10 AWG with rating of 30 A at 60 C is suitable [ Refer NEC Table 310.15(B)(16)]
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Question 4 of 10
4. Question
How many number of 500 kcmil THWN conductors that can be installed in a 4 in. * 4 in. wireway?
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Wireway area = 4 * 4 = 16 sq. in.
Refer NEC [376.22(A)]
The conductor fill area should be maximum 20% of wireway area.
WireWay conductor fill = 16 * 0.2 = 3.2 sq. in.
Area of 500 kcmil THHN = 0.7073 sq in. [Chapter 9, Table 5]
Number of 500 kcmil THWN conductors = 3.2 / 0.7073 = 4.5 ( 4 conductors)
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Question 5 of 10
5. Question
If a service is fed by three parallel sets of 400 kcmil conductors, what is the required conductor size for GEC?
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The total underground conductor size = 3 * 400 = 1200 kcmil
.Refer NEC Table 250.166
.The required GEC is 3/0 AWG for 1200 kcmil size
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Question 6 of 10
6. Question
Which of the following is the size of single supply-side bonding jumper is required for three metal raceways, each containing 300 kcmil service conductors?
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Refer: NEC Table 250.102(C)(1)
For over 3/0 AWG and 350 kcmil the required bonding jumper size is 2 AWG
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Question 7 of 10
7. Question
If the length doesn’t exceed ………. Feet the cord and plug connections are allowed for swimming pool pump motors?
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Question 8 of 10
8. Question
After the demand factor is applied , what is the general lighting load of a hospital which is having 80,000 sq ft area?
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As per NEC Table 220.12 , The unit general lighting load for hospital is 2 VA per sq ft.
So total lighting load of hospital = 80,000 * 2 = 1,60,000 VA
As per NEC Table 220.42 The lighting load demand factors are as follows
First 50000 or less 40% i.e
50,000 * 0.4 = 20000
Reaming is 20%
1,10,000 * 20 = 22000
So total lighting load after demand factor is applied = 20000 + 22000 = 42000 VA
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Question 9 of 10
9. Question
A 115/230 delta configured three phase transformer is rated at 45 KVA. What is its high-leg voltage of the transformer secondary?
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A delta connected transformer high leg voltage = ( Line voltage /2 ) * 1/732
High leg voltage = 230/2 * 1.732
High leg voltage = 199 Volts
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Question 10 of 10
10. Question
What is the maximum size over current device is required for a 4200 W, 240 V electric water heater connected in a building.
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Protection rating for an electric water heater should be less than 150% of the rating of device.
Protection size = 4200 / 240 * 1.5
Protections size = 26.25 A
The nearest next size over current device is 30 A.