What type of switching device must be used with a shunt trip breaker?

A shunt trip breaker is designed to automatically trip the circuit when a specific condition occurs, such as a remote signal indicating a fault or danger. For this to work effectively, it needs a switching device that can supply a momentary signal to the breaker to trigger the trip mechanism.

A normally open switch is perfect for this purpose since it remains open during normal operations and only closes to send a signal when a trip is necessary. This ensures that the circuit remains energized until the need to trip arises, preventing unnecessary interruptions in operations. It's also important to note that the moment when the switch closes is crucial, as it activates the shunt trip.

In contrast, the other types of switches wouldn't provide the required operational functionality. A normally closed switch would be inappropriate, as it would continuously allow current through until it is manually opened, and a toggle switch could either be normally closed or normally open, which means it wouldn’t guarantee the necessary functionality. A momentary switch, while it can potentially serve a similar purpose, does not specifically define the state of operation required for the shunt trip to function effectively. Therefore, the normally open switch is the most suitable choice for use with a shunt trip breaker.