Motor Circuit Calculations (NEC Code 430) -1
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Question 1 of 9
1. Question
1 pointsWhat is the ampacity of a conductor that supplies a single phase motor used in continuous duty applications?
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Ref : NEC 430.6
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Question 2 of 9
2. Question
1 pointsA Single phase continuous duty motor has a full load current (FLC) of 20 amperes. Which of the following is the ampacity of conductor that should used to supply the power to the motor.
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Refer : NEC 450
The conductor ampacity shall not be less than 125% of FLCSo 20 * 1.25 = 25 amperes
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Question 3 of 9
3. Question
1 pointsWhich of the following type of conductor is used to supply a 40 ampere single phase motor used for continuous duty applications?
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Refer : NEC 450
The conductor ampacity shall not be less than 125 % of motor FLCConductor ampacity : 1.25 * 40 = 48 ampere
Refer NEC Table 310.16
The suitable conductor in the options is No 8 THW -
Question 4 of 9
4. Question
1 pointsWhich of the following is the allowed full load current (FLC) of a 5 HP, 230 volts single phase AC motor?
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Refer : NEC Table 430.248
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Question 5 of 9
5. Question
1 pointsWhich of the following is the overload protection rating of a 2 HP 230 volts single phase motor used in continuous duty applications. The service factor of a motor is 1.1.
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Refer : NEC Table 430.248
As per Table Full load current (FLC) of a 2 HP single phase motor = 12 ampersRefer : NEC 430.32 (A)(1)
When the service factor is 1.1 then
overload protection = 115 % * FLC
1.15 * 12 = 13.8 amperes -
Question 6 of 9
6. Question
1 pointsA 50 HP 460 volts three phase AC motor is supplied with THWN conductors. Which is of the following is the size of the branch circuit conductors?
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Refer: NEC Table 430.250
Full load current (FLC) = 65 ampere
Branch circuit conductor size = 125% of 65 = 1.25 * 65 = 81.25 amperes (85 amperes Nearest one) -
Question 7 of 9
7. Question
1 pointsTwo motors 15HP and 5 HP motors are operated at 230 volts and connected to a single feeder. Which of the following is the size of feeder conductor?
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Motor FLC Using Table 430.250
15 HP -> 42 amperes
5 HP -> 15.2 amperes
Size of feeder circuit ( Refer NEC 430.24)
15 HP -> 42 * 1.25 = 52.5 A
5 HP -> 15.2 = 15.2 A
= 67.7 A -
Question 8 of 9
8. Question
1 pointsIf a 20 ampere ac snap switch is used to disconnect a 1.5 Hp motor what must be the maximum full load current of a motor?
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Refer: NEC 430.109 (c) (2)
A Snap switch used to disconnect a motor where full load current rating should be less than 80% of ampere rating of a switch.
Maximum motor full load current = 20 * 0.8 = 16 Amperes
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Question 9 of 9
9. Question
1 pointsIf the motors operate at or over ……….. volts , the live parts of the motor must be guarded.
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Incorrect
Refer: NEC 430.232