Emergency circuits may be powered by holding which type of circuit breaker?

Emergency circuits are designed to remain operational under various conditions, including power failures or emergencies. Holding a circuit breaker serves to maintain power to crucial emergency systems.

For emergency circuits, non trip-free circuit breakers are particularly relevant because they can be manually held in the "on" position, ensuring that the circuit remains powered even if there’s a fault condition or an overload. This feature is vital in emergencies where sustained power is essential for safety systems such as lighting, communication, or critical flight instruments.

In contrast, trip-free circuit breakers are designed to trip automatically if an overload condition occurs, which could lead to a loss of power when it is most needed. Resettable circuit breakers allow for a reset after a fault condition, but they do not inherently guarantee power sustainment under emergency circumstances provided by the manual hold of the circuit. Fuse-based systems would also not allow for holding power through manual intervention, as fuses are designed to fail completely once overloaded.

Thus, the key characteristic of non trip-free circuit breakers enables emergency power retention, underscoring their importance in maintaining functionality during critical situations.