400 Hz external power shall include which safety feature?

• A. Grounding Strap
• B. Overload Relay
• C. Interlock Circuit
• D. Emergency Stop

Answer: (C)

When you’re connecting 400 Hz external power, the safety focus is on preventing energization under unsafe conditions. An interlock circuit ensures the power can only be applied when all safety conditions are met—typically by tying the power switch to the physical state of the equipment (for example, a connector seated properly or a access panel closed). This prevents live electricity from being connected while a panel is open or during improper setup, reducing the risk of shock, arcing, or damage during maintenance.

Grounding straps help discharge static and establish a reference ground but don’t control whether the external power can be energized. An overload relay protects wiring and equipment from excessive current, but it doesn’t enforce safe conditions before energizing. An emergency stop cuts power in an emergency, but the interlock specifically prevents energization until safe conditions are present. So the interlock circuit is the safety feature that best fits safeguarding 400 Hz external power connections.