S-IR thermal overload relays are designed for use with S-ID(X) contactors. They protect motors against thermal overload, which appears when current intake is too high. S-IR thermal relays consist of the starting and the contacting section. Bimetal strips, heated by the current flow-through bend and activate the disconnecting system (through the release bar). This breaks the circuit of contactor steering current. Relays construction has been specially designed and withstands the “test finger” trial.

S-IR thermal relays can be fitted into corresponding S-ID or S-IDX contactors, or with use of a special mounting device, mounted beside them on their own. Relays wearing K-ERB symbol are used to protect electric machinery against overloads occuring during their continuous work, while K-ERS relays protect devices against the effects of short circuit. As the short-circuit protection they break the circuit, while the overvoltage release activates the breaker switch if short-circuit current flows through the relay.