Over Current Protection Quiz Test Questions-2 : ( NEC Code)
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Question 1 of 10
1. Question
1 pointsTo protect a 12 AWG conductor what must the electrical fuse size?
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Refer : NEC 240.4(B)
The fuse size must not exceed the conductor rating
Refer : NEC Table 310.15(B)(16)
12 AWG maximum allowable ampacity is 20 amperes
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Question 2 of 10
2. Question
1 pointsOn a residential electric service which of the following conductors need over current protection?
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Refer: NEC 240.25
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Question 3 of 10
3. Question
1 pointsThree single phase motors with full load current rating of 20,30,25 amperes respectively are connected to 240 volts electrical circuit. Which of the following is the required dual element fuse size can be used for the circuit?
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Refer: NEC Table 430.52
The fuse size should be 175% of largest full load current motor plus all the other full load current motors.
Fuse rating = 1.75 * 30 + 20 + 25 = 97.5 amperes ( 110 amperes)
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Question 4 of 10
4. Question
1 pointsWhen a fuse or circuit breaker is used as over current protection device, they shall be connected …………………..
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Question 5 of 10
5. Question
1 pointsIn an electrical system at what point branch circuit over current protection device should be located?
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Refer: NEC 240.21
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Question 6 of 10
6. Question
1 pointsA multi wire branch circuit may supply only ………….. if it is protected by fuses.
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Refer : NEC 210.4 (C)
Multi wire branch circuits shall supply only line to neutral loads
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Question 7 of 10
7. Question
1 pointsA resistance welder connected to electrical system should maximum over current device rating …………….. of the rated primary current of the welder?
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Maximum 300% of the rated primary current of welder
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Question 8 of 10
8. Question
1 pointsWhat is the maximum over current device rating required for an auto transformer that has a full load current of 50 amperes?
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Refer : NEC 450.4(A)
If maximum over current device rating should be 125 % of full load input current
50 * 1.25 = 75 amperes
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Question 9 of 10
9. Question
1 pointsThe allowable ampere rating of bus conductor is 48 amperes. What is the maximum allowable rating of over current device?
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Incorrect
Refer : NEC 240.4 (B)
48 amperes rating is not a standard fuse rating. So next higher standard rating 50 amperes can be taken
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Question 10 of 10
10. Question
1 pointsWhat is the smallest rating plug fuse that is used for residential 120 volts branch circuit?
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Refer : NEC 240.6(A)
The standard fuse ratings are 15,20,25,30 amperes, so 15 amperes is the smallest fuse rating.