The 400 Hz external power interlock safety requirement is provided by which component?

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

Answer: (C)

The safety control that governs when external 400 Hz power can be connected is the interlock circuit. This circuit is specifically designed to enforce safe conditions before power is supplied, preventing accidental connection or arcing and ensuring proper sequencing between the external source and the aircraft systems. It monitors the status of connectors, switches, and related safety conditions and locks or unlocks the power path accordingly.

The other components serve different roles: an overload relay protects the circuit from overcurrent but doesn’t manage whether external power can be connected; an emergency stop halts equipment but doesn’t control the interconnection sequence; a grounding strap provides a fault path for safety grounding, not interlock control. Therefore, the interlock circuit is the component that provides the 400 Hz external power interlock safety requirement.