OLR

Overload Relays

The Siemens solid-state overload relays up to 630 A with internal power supply have been designed for current-dependent 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 motor rated 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 operating current and is stored in the form of a long-term stable tripping characteristic (see Characteristics). The "tripped" status is signaled by means of a switch position indicator (see Functions). The contactor is either reset manually or automatically (see Functions) after the recovery time has elapsed (see Functions).

The devices are manufactured in accordance with environmental guidelines and contain environmentally friendly and recyclable materials. They comply with important worldwide standards and approvals.