Sigma Series

Danotherm ZRF Sigma resistors are modular ceramic wire wound resistors that cool through convection cooling. The resistor modules are fitted with a protection grid to prevent accidental contact with the hot resistor surface.

Danotherm's ceramic wire wound resistors consist of an active wire wound around a ceramic core. Based on a cordierite core, the ZRF Sigma resistors provide high resistance to temperature changes. A coating of aluminum phosphate protects the wire and efficiently transfers heat to the ceramic core. According to the customer's requirements, alloys, materials, and core materials are chosen.

The nominal power ratings for Sigma ZRF resistors range from 180 W to 5 kW, and working voltages range from 400 to 850 Volts. The resistors can withstand 10 times the nominal power during 5s with a cycle time of 120s.

For detection against overheating, an optional thermostat is available. Connection boxes are also available as options. UL-approved Sigma resistors are available on request.

Protection ratings for Danotherm ZRF Sigma resistors range from IP20 to IP21. Typical applications include filters, charging/discharging circuits, and brake resistors.