Question

Three #10 AWG copper wires with type TW insulation are run in an attic crawl space where the ambient temperature will remain at 120° F. What's the largest load in amperes that these wires may carry?

a) 20 amperes
b) 25 amperes
c) 30 amperes
d) 35 amperes

Answer 1

The largest load that the three #10 AWG copper wires with type TW insulation may carry in the attic crawl space is 17.4 amperes.

Step-by-step explanation:

The largest load in amperes that the three #10 AWG copper wires with type TW insulation may carry can be determined using the current-carrying capacity of the wire. For #10 AWG copper wire, the current-carrying capacity is approximately 30 amperes. However, this value is based on the assumption of a 30° C ambient temperature. Since the ambient temperature in the attic crawl space is 120° F (approximately 48.9° C), the current-carrying capacity will be reduced.

To calculate the adjusted current-carrying capacity, we can use the temperature derating factors provided by the National Electrical Code. From Table 310.15(B)(2)(a) of the NEC, at 120° F ambient temperature, the temperature derating factor for #10 AWG copper wire is 0.58.

Therefore, the largest load that these wires may carry is 30 amperes multiplied by the derating factor of 0.58, which equals 17.4 amperes.