Control Power

The P trip unit is designed to be used with an external 24 Vdc power supply. The large LCD display used by the P trip unit requires too much current to be powered by current flow through the circuit breaker.

The P trip unit has a circuit voltage power supply which will power the trip unit when there is approximately 150 Vac or more between two phases. The standard configuration for the voltage probes inside the circuit breaker is at the bottom connections. If the circuit breaker is open in a top fed application, there is no voltage at the bottom of the circuit breaker and the trip unit will not be powered.

The following will be powered and functional even if the trip unit is not externally powered:

Fault protection for LSIG functions. The P trip unit is fully circuit powered for fault protection.
LED trip indication (powered by an onboard battery). The battery’s only function is to provide LED indication if all other power is off.
Ground-fault push-to-trip button works for testing ground fault when the trip unit is powered by the circuit voltage power supply. The ground-fault push-to-trip is also functional if a Hand-Held Test Kit or Full-Function Test Kit is powering the trip unit.

The following will be powered and functional with external power:

All of the above functions which are functional without external power.
LCD display and backlight are functional. Backlight intensity is not controlled or adjustable, and may be different from one trip unit to another.
All metering, monitoring, and history logs are functional.
Communications from the trip unit to M2C and M6C programmable contact modules are powered by a 24 Vdc power supply at F1 and F2. The M6C also required an external 24 Vdc power supply.
Modbus communciations are functional, using a separate 24 Vdc power supply for the circuit breaker communications module. This separate 24 Vdc power supply is required to maintain the isolation between the trip unit and communications.
The ground-fault push-to-trip is also functional if a Hand-Held Test Kit or Full-Function Test Kit is powering the trip unit.