Motor Heater

You might be referring to something like this: http://www.ab.com/en/epub/catalogs/12768/229240/229258/229579/tab5.html

When the motor is not running, this device puts a small DC voltage to the winding, using the winding itself as a heater to keep condensation from forming in the motor.

The motor space heaters are generally looks rigid circular ring shaped and fixed it in both side of the motor winding. It is readily visible if the motor side cover is opened. However, they may be flexible as well. Here is a link to see the flexible motor heater.

http://www.minco.com/uploadedFiles/Products/Thermofoil_Heaters/hr1-anti-condensation.pdf

Generally, the motor above 15 HP require the anti-condensation heater. See this link: http://cr4.globalspec.com/thread/43408/Space-Heater-Calculation

- MS