NEC Code Questions Practice Test-10
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Question 1 of 10
1. Question
1 pointsWhat is the required size of a neutral conductor for a dwelling unit with a calculated load of 220 A. The unbalanced load is 120 A and service disconnect rating is 250A.
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Answer: 1 AWG
83% deduction is not applicable for neutral conductor so the conductor size should be rated 100% of unbalanced load.
Refer : NEC Table 310.15(B)(16)
1 AWG is suitable as neutral conductor which ampacity of 130 A ( 75 C)
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Question 2 of 10
2. Question
1 pointsIf 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 3 of 10
3. Question
1 pointsA 400 breaker protects a set of 450 kcmil feeder conductors. A feeder fed from 450 kcmil feeder that supply disconnects with 25 A over current device. What is the minimum size conductor for these tap?
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Answer : 8 AWG
The over current device 25 A is less than 10 percent of the rating of the feeder breaker (400A.) As per code it cannot be less than 40 A.
Refer : NEC Table 310.15(B)(16)
so 8 AWG at 40A 60 C is the minimum size required.
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Question 4 of 10
4. Question
1 pointsWhat size service entrance conductors are required for 250 A continuous three phase load if the terminals are at ambient temperature of 70 C?
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Incorrect
The load is continous so the service entrance 125% rated ampacity
Service entrance ampacity = 1.25 * 250 = 312.5
According to NEC Table 310.15(B)(16) at 75 C 400 kcmil conductors with rating of 335 amperes are suitable has service conductors.
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Question 5 of 10
5. Question
1 pointsUnder which of the following condition the on-site generator is not considered as separately derived system?
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Refer : NEC 250.30 Note 1
The alternating generator is not considered as separately derived system as long as the neutral is coupled with service system neutral
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Question 6 of 10
6. Question
1 pointsWhen the circuits are protected by a over current device rating of 1000 A, what size bonding jumper is required for each metal raceway?
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The bonding jumper must be sized in accordance with NEC Table 250.122 if the circuits are protected by over current devices.
Refer : NEC Table 250.122
The 2/0 AWG copper conductor is suitable size, if the over current device rating is 1000 A
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Question 7 of 10
7. Question
1 pointsWhen five conductors each with an ampacity of 25 A bundled through NM cable, what is the adjusted ampacity of each cable.
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When multiple conductors are equipped in a single cable, the ampacity should be adjusted according to Table 310.15(B)(3)(a).
So for five conductors the adjustment factor is 80% or 0.8
The adjusted ampacity of each conductor = 25 * 0.8 = 20 Amperes
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Question 8 of 10
8. Question
1 pointsA 40 KVA , 480 V three phase transformer has a primary over current protection device is rated at 75 A. What is the size of primary conductor that can be used?
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The primary current = 40000 / (480 * 1.732) = 48 A
The primary conductor should be rated 125 % of primary current
48 * 1.25 = 60A.
Refer : NEC Table 310.15(B)(16)
4 AWG with 70 A at 60 C is suitable as primary conductor
This conductor can be protected 75 A OCPD.
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Question 9 of 10
9. Question
1 pointsHow 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 10 of 10
10. Question
1 pointsWhat size service entrance conductors are required for 250 A continuous three phase load if the terminals are at ambient temperature of 70 C?
Correct
Incorrect
The load is continuous so the service entrance 125% rated ampacity
Service entrance ampacity = 1.25 * 250 = 312.5
According to NEC Table 310.15(B)(16) at 75 C 400 kcmil conductors with rating of 335 amperes are suitable has service conductors.