23 Jul 2024


Space-saving motor protection relays are Atex-certified

Siemens has announced a new generation of motor-protection relays designed to protect motors against overheating by measuring the temperatures at points at risk of overheating in a motor using PTC (positive temperature coefficient) thermistors integrated into the windings. The Sirius 3RN2 relays replace the earlier 3RN1 series and, with widths of 17.5 and 22.5mm, need less space in control cabinets.

The relays have wide supply voltage ranges so that one device can cover supply voltages around the world.

The relays can be used in hazardous areas, and are certified to Atex and SIL 1, in accordance with EN 50495. They are suitable for either gas- or dust-laden atmospheres, allowing them to be used in difficult conditions, such as those found in the oil, gas and chemical industries, and in mills and sawmills.

The relays are designed for use where circuit-breakers or overload relays would not provide adequate protection. In such cases, the motor may overheat if, for example, a fan fails or the ambient temperature is too high. Typical applications include starting centrifuges, braking, and performing frequent switching in jogging and reversing operations. They can also be used where motor cooling could be impaired by contamination – for example, in the paper and textile industries, and in cement works.

Commissioning is said to be easy. No parameters need to be assigned, reducing the risk of errors, while commissioning does not need detailed knowledge of a motor, such as its maximum operating temperature.