Motor protection relay

The motor protection relay is also referred to as overload relay and operates on the same principle as the motor protection switch. The motor does not directly trip automatically, however.

When an overload relay trips, for example, smaller (auxiliary) contacts that typically control a contactor (electronic switch) are switched. The contactor then trips the consumer. An overload relay does not have a short-circuit trip (short-circuit release). The thermal trip provided for this purpose (see bimetal) might respond too slowly in the event of a short circuit so that fuses must be fitted in the motor power cables to safeguard motor protection.