On a heavy starting duty wound rotor motor, the secondary resistor leads must have current capacity of at least what percent?

• A. 35%
• B. 45%
• C. 85%
• D. 110%

Answer: (B)

In a wound-rotor motor with external starting resistors, the leads that carry current into the rotor resistors must be sized to handle the starting current. For heavy starting duty, the minimum acceptable rating is about 45% of the motor’s full-load current. This rating provides enough capacity to carry the starting rotor current through the resistor network without overheating, while avoiding overdesign. Choosing a value much lower than this risks overheating the leads during frequent or heavy starts, while a much higher rating would add unnecessary cost.