Thermasentry

Therma-Sentry

Therma-Sentry is a thermal protection system that is activated by excessive winding temperature. Therma-Sentry protects against the most common causes of motor failure including: high or low supply voltage, unbalanced line voltage, single phase conditions, abnormally high ambient temperatures, blocked ventilation, starting overload and running overloads.

The system consists of three (3) PTC thermistors embedded in the motor winding end turns, one per phase, with the leads connected to a solid state electronic controller. The solid state controller can be supplied permanently potted in the main or accessory outlet box, or as a separate module.

The leads from the three (3) thermistors are connected internally in the ‘common lead circuit’ configuration.

The Therma-Sentry system will only provide locked rotor protection for certain motors. In form-wound motors, the winding insulation is so heavy the temperature gradient across the insulation to the thermistor is too great to give the rapid response required to prevent rotor failure. Also, for mush wound motors, only motors with a winding safe stall time less than the rotor safe stall time will have locked rotor and starting overload protection.

Selection

The Therma-Sentry controller has one normally closed (N.C.) contact with a 3 amp control circuit rating. Thus the Therma-Sentry system is generally used in applications where the motor is shut down when excessive temperatures occur. On customer orders, unless the customer order specifically requires thermistors rated for alarm temperatures, thermistors for shut-down temperatures are supplied.

The Therma-Sentry controller is available in two styles:

1.) Therma-Sentry service module - typically for NEMA frames 440 and TITAN frames 449 and larger

2.) Therma-Sentry assembly - typically for NEMA frames 400 and smaller, or FLA under 240 amps.

When specifying Therma-Sentry at time of order entry, make sure to note:

MOUNTING: Motor mounted (MM) or Separately mounted (SM)

VOLT SOURCE: U.S. Motors only provides separately excited (SE). The control module must be separately excited by either 115, 230, 460, or 575 volt source, or 380 volt/ 50 hertz. If not specified, 115v will be supplied.

The most common specification is motor mounted, separately excited (MMSE).

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