Siemens Overload Relays

Siemens Sirius 3RU and 3RB thermal and solid state overload relays

The 3RU1 and 3RU 2 thermal relays are designed for overload protection of 3 phase and single phase applications.  The rise in current heats up the bi-metal strips causing the auxiliary contacts to trip which in turn cut power to the control voltage of the contactor.  For resetting a set recovery or cooling time must be achieved and then, depending on whether manual or automatic reset has been chosen, the overload relay will reset and allow power back to the contactor.

The 3RB2 and 3RB electronic relays are solid state and provide for a wider range of possible AMP settings.  These relays detect an over current state by a set of current transformers contained within the unit and trip the auxiliary contacts for an extra later of protection for the motor.  In addition to this level of protection, the Sirius 3RB series also allow for internal ground fault detection which is a feature not available in their 3RU counterparts.

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