Thermistor Relays

Electric motors are significant investments, and losing them to overheating just isn't an option. Sprecher + Schuh's RT7-E1 and RT7-E2 Thermistor Protection Relays are designed to keep that from happening.

The RT7 is not a replacement for an overload relay. Instead, it is additional protection from damaging heat build-up in the motor.

If you have thermistors...

Installed in many of today's electric motors, thermistors sense heat levels produced in the stator windings. If thermal levels exceed safe standards, thermistors send that information to the relay, which trips and switches off the motor. The RT7-E1 and RT7-E2 display a red LED to indicate a fault.

The RT7-E1 and RT7-E2 also trip because of a short or open in the sensor measuring circuit. Each relay displays an open circuit alert with a 2 Hz red LED and a short circuit warning with a blinking red LED. The RT7-E2 stores a motor's switching status in memory during power failures - a critical safeguard.

Compatibility and convenience

These relays and their microprocessor technology provide very accurate and repeated protection. Neither requires adjustment, and their broad supply voltage rating (24...240V AC/DC) makes them ideal for a wide variety of applications. Up to six PTC thermistors can be connected in series.

Automatic reset

the RT7-E1 and RT7-E2 automatically reset if the sensor measuring circuit's resistance drops below the reset value. To keep a motor from restarting after automatic reset, provide three-wire momentary control. The RT7-E2 also has a manual reset button, as well as terminals for remote reset.