Electronic Overload Relays 3RB3123

3RB31 solid-state overload relays up to 80 A with internal power supply have been designed to provide current-dependent protection for loads with normal starting and heavy starting against impermissibly high temperature rises due to overload, phase asymmetry or phase failure. An overload, phase asymmetry or a phase failure results in an increase of the motor current beyond the set rated motor current. This current rise is detected by the current transformers integrated in the devices and evaluated by corresponding solid-state circuits which then supply a pulse to the auxiliary contacts. The contacts then disconnect the load via a contactor. (The contactor function is not an integral component of the overload relay). In addition to current-dependent protection for loads against impermissibly high temperature rise caused by overload, phase asymmetry, and phase failure, 3RB31 solid-state overload relays feature internal ground-fault detection (not possible in conjunction with contactor assemblies for star-delta (wye-delta start). This provides protection of loads against highimpedance faults to ground caused by damaged insulation, moisture, condensation, etc