A shunt trip breaker is a type of circuit breaker that, in addition to automatically tripping during an electrical surge and cutting off power, also can be triggered by a separate electrical signal to disconnect before a power surge occurs. A shunt breaker has three connections: to the power source, the output, and a third contact usually hooked into a safety system such as a smoke detector.
The first two contact points of a shunt breaker are connected by a metallic strip on a switch, and an electromagnet placed underneath this switch. Electrical power flows through the strip under normal circumstances. When a surge occurs, the magnet has enough power to activate, throwing the switch and breaking the connection. In a shunt trip breaker, the magnet is also wired to an external system, which can send an electrical signal that will also activate the magnet and trip the switch. After the switch has been tripped, it must be manually reset.
Shunt trip breakers are often used in concert with sprinkler and other fire suppression systems that can potentially short-circuit electrical appliances. The shunt breaker is connected to the fire detector or alarm, so that when the alarm is triggered, the breaker is automatically tripped, cutting the power to any computers, electronic locks or other electrical equipment before the sprinklers can soak them in water.