3RB3123-4VB0

The 3RB30/3RB31 overload relays up to 40 A with internal power supply have been designed for inverse time delayed protection of loads with normal and heavy starting against excessive temperature rises due to overload, phase unbalance or phase failure. An overload, phase unbalance or phase failure result in an increase of the motor current beyond the set rated motor current. This current rise is detected by the current transformers integrated into the devices and evaluated by corresponding solid state circuits which then output a pulse to the auxiliary contacts. The auxiliary contacts then switch off the load by means of a contactor. The break time depends on the ratio between the tripping current and current setting Ie and is stored in the form of a long term stable tripping characteristic. In addition to inverse time delayed protection of loads against excessive temperature rises due to overload, phase unbalance and phase failure, the 3RB31 solid state overload relays also allow internal ground-fault detection (not possible in conjunction with contactor assemblies for wye delta starting). This provides protection of loads against high resistance short-circuits due to damage to the insulation material, moisture, condensed water.