By Bert Markgraf
Updated Mar 24, 2022
Shunt‑trip circuit breakers are typically rated for three‑phase, 480 V or higher systems. They are installed like any other three‑phase breaker, but include additional remote control circuits that allow an operator to trip the breaker from a distant location and to monitor its status. While the shunt‑trip can function as a remote switch, frequent use for normal switching can reduce the breaker’s lifespan, so it is best reserved for fault‑condition trips.
1. Disconnect the supply to the circuit where the breaker will be installed. 2. Mount the breaker in the panel and connect the three phase conductors to the line‑side terminals. 3. Wire the load conductors to the load‑side terminals. 4. Install a control transformer to step down the voltage to 120 V AC. 5. Connect the two line‑side terminals of the transformer to two of the load‑side phases. 6. Run the 120 V AC output to fuses sized for the transformer's nameplate current. 7. Route one fuse to a terminal; route the other to one side of the shunt trip and one side of the breaker’s auxiliary contact (closed when the breaker is closed). 8. Wire the opposite sides of the shunt trip and auxiliary contact to separate terminals.
Run three conductors from the breaker panel to the remote operator station:
Provide the operator with a push button to trip the breaker and a pilot light to indicate status. Connect the 120 V AC supply to one side of the push button and the pilot light. Connect the shunt‑trip line to the other side of the push button, and the auxiliary contact line to the other side of the pilot light.
1. Restore power to the circuit. 2. Manually close the breaker and verify the pilot light illuminates at the remote station. 3. Press the push button to trigger the shunt trip; the breaker should open and the pilot light should extinguish.
