Abstract: This trip circuit comprises a DC source and the series combination of a trip coil and a thyristor connected across the source. Connected between the source and the gate circuit of the thyristor is a triggering circuit including protective relay contacts that are operable to cause current from the source to flow through the triggering circuit and the gate circuit, thus firing the thyristor to produce effective energization of the trip coil. For producing effective energization of the trip coil in the event that the thyristor fails to fire, there is provided back-up energizing means in the form of a low ohmic resistor connected externally of the thyristor between its gate circuit and its cathode for providing a conductive path in series with the trip coil and the triggering circuit through which effective energizing current from the source can flow through the trip coil.