A hermetic refrigerant motor-compressor's branch-circuit short-circuit and ground-fault protective device shall be capable of carrying what percent of the motor's starting current?

• A. 80
• B. 125
• C. 175
• D. 100

Answer: (D)

When sizing the protective device for a hermetic refrigerant motor-compressor, the important factor is the inrush current—the starting current. At startup the motor draws a large surge that can be many times its running current. The branch-circuit short-circuit and ground-fault protective device must be able to carry that startup current without nuisance tripping, so it is rated to handle the motor’s starting current. That means the device’s capacity is aligned with 100 percent of the starting current.

In other words, the protection must accommodate the high inrush just long enough to start the motor, while still providing protection if a fault occurs. The other percentages would not reflect the requirement to tolerate the full starting current. Therefore, the correct value is 100 percent.