Winding thermostats are snap-action, bi-metallic, temperature actuated switches normally installed in the connection end turns of the motor winding. Their purpose is to activate a warning device, or shut down the motor upon excessive winding temperatures.

Thermostats are made with contacts that are either normally closed (N.C. - open at high temperatures) or normally open (N.O. - closed at high temperatures). The thermostat temperature switch point is pre-calibrated by the manufacturer and is not adjustable. Reset is automatic after a decrease in temperature. This feature allows the motor to cool before restarting. No control unit is required for use with thermostats.

The normal procedure is to wire three thermostats together as a set, with one thermostat embedded in each phase. Normally open thermostats are wired in parallel internal to the motor. Generally normally open thermostats are used to activate a warning alarm (bell, light, etc.)

Sometimes a customer will specify dual thermostats. One set of normally open thermostats having different temperature trip points are usually chosen. Unless specified by the customer, the alarm thermostats usually have a trip point approximately 10°C lower than the shutdown thermostats.


1. If the customer does not specify alarm or shutdown thermostats, shutdown thermostats with shutdown temperature ratings will be supplied.

2. Thermostat switch point is based on motor temperature rating (insulation class), or on customer requirement.

3. The type of thermostat is based on the defined function or purpose (alarm or shutdown). Our Engineering Department usually chooses the type of thermostat from those available for a particular purpose.

4. U.L. explosionproof motor requirements specify particular thermostat temperature ratings. All dual label and Class II explosion proof motors must have quantity three (3) N.C. thermostats, not to exceed the temperature rating necessary to shut down the motor.

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