Which of the following statements is true regarding override capabilities of Phase one and Phase two modes with respect to the shunt trip?

• A. Neither Phase one nor Phase two modes can override the shunt trip function
• B. Phase two mode can override the shunt trip function
• C. Phase one mode can override the shunt trip function
• D. Both Phase one and Phase two modes can override the shunt trip function

Answer: (A)

Shunt trip is a protective, remote-disconnect signal that must cause an immediate open of the circuit to isolate a fault or unsafe condition. Allowing either phase mode to override this function would let the protection be bypassed, defeating the purpose of the shunt trip and potentially creating a hazardous situation. Because safety and rapid isolation are priorities, the control logic is designed so that neither Phase one nor Phase two modes can override the shunt trip. Maintenance or testing would use separate, explicitly approved procedures, not an override of the normal protective function.