This relays are designed for instantaneous phase or earth fault protection and instantaneous high set over current protection.; A standard hinged-armature unit forms the basic movement for this relay. It consists an operating coil mounted on a cylindrical iron core bolted to a frame at one end. This frame extends along the side of the coil, with its end forming a knife-edge on which the armature is pivotally mounted. The armature is 'L' shaped and pivoted at its corner so that one arm can be attracted to the end of the core while the other arm to operate a set of contacts.