SIRIUS 3RU2 Thermal Overload Relays

Siemens SIRIUS 3RU21 thermal overload relays are suitable for customers from all industries who want to guarantee optimum inverse-time delayed protection of their electrical loads (e.g. motors) under normal starting conditions (Class 10, 10A). 3RU21 thermal overload relays up to 100 A have been designed to provide current-dependent protection for loads with normal starting against impermissibly high temperature rises due to overload or phase failure. An overload or phase failure increases the motor current beyond the set rated motor current. Through heating elements, this current rise heats the bimetal strips inside the device which then bend and trigger the auxiliary contacts using a tripping mechanism. The auxiliary contacts then switch off the load utilizing a contactor. The break time depends on the ratio between the tripping current and the current setting and is stored in the form of a long-term stable tripping characteristic curve.

The "tripped" status is signaled by a switch position indicator. The relay is reset manually or automatically after a recovery time has elapsed. The 3RU2 thermal overload relays are suitable for operation with frequency converters. The devices are manufactured in accordance with environmental guidelines and contain environmentally friendly and reusable materials. They comply with all important worldwide standards and approvals.

The 3RU2 overload relays are certified in accordance with both the European explosion protection directive (ATEX) and the international explosion protection standard (IECEx), see https://support.industry.siemens.com/cs/ww/en/ps/16271/cert.