What is the primary function of relay contacts that are normally closed?

The primary function of relay contacts that are normally closed is to complete the circuit during normal operation. In a normally closed relay configuration, the contacts allow current to flow through the circuit when the relay is not energized. This means that in its default state, power is supplied to the connected device or circuit.

This functionality is crucial in applications where it is necessary to maintain power to a load or component until a specific condition is met that activates the relay. Upon energizing the relay (often through a control signal), the contacts open, interrupting the flow of current and thus providing a way to control the operation of the circuit by cutting off power when needed.

In contrast, the other options address different roles or behaviors that do not align with the primary function of normally closed contacts. For instance, interrupting the circuit during testing is typically associated with other configurations or practices, overload protection often involves circuit breakers or fuses rather than relays alone, and safety disconnects require specific designs to ensure total isolation, which is not the default characteristic of normally closed contacts.