Question 10.6: Assume that a motor with a full-load current rating of 28 A ......
Assume that a motor with a full-load current rating of 28 A is to be connected with copper conductors that have Type THW insulation. The motor is located in an area with an ambient temperature of 30°C. The motor is not marked with N E M A^{\circledR} code letters, and the termination temperature is not known. What size conductors should be used?
Since a motor load is continuous, multiply the full-load current rating by 125%:
28 ~A \times 1.25=35~ A
Refer to N E C^{\circledR} Table 310.16. Type THW insulation is located in the 75°C column. Although this conductor is located in the 75°C column, the wire size must be chosen from the 60°C column because the termination temperature is not known and the motor does not contain N E M A^{\circledR} code letters. The nearest wire size without going under 35 A is an 8 AWG. For circuits with a current of 100 A or greater, N E C^{\circledR} 110.14(C)(1)(b) permits conductors to be selected from the 75°C column.