What size THHN conductor is required to feed a 16A noncontinuous load when the c

Question

What size THHN conductor is required to feed a 16A noncontinuous load when the conductors are in an ambient temperature of 100°F in a dry location? The circuit is protected with a 20A overcurrent device. What size THHN conductor is required to feed a 16A noncontinuous load when the conductors are in an ambient temperature of 100°F in a dry location? The circuit is protected with a 20A overcurrent device. What size THHN conductor is required to feed a 16A noncontinuous load when the conductors are in an ambient temperature of 100°F in a dry location? The circuit is protected with a 20A overcurrent device.

Explanation / Answer

Given that

THHN conductor need to feed non continuous load of 16 A at 1000 F or 37.770 C

Protection device current rating is 20 A

As we know cable should not burnt if current flow of 20 A*1.25 = 25 A, as protection device operates when current is 20 A. 1.25 is safety factor.

Actual current is 16 A noncontinuous load size of THHN conductor required, which operated in dry locations, ambient temperature of 1000 F or 37.770 C is

10 AWG - 30 A - 600 C - THHN Cable required.

Maximum current in cable considering safety factor of 1.25 is = 1.25 * 16 = 20 A

If we choose 20 A cable i.e 12 AWG - 20 A - 600 C , the cable will burn before protection device operates. It is better to use higher rating cables than protection devices rating.

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