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Resistance Temperature Detectors (RTDs)

RTDs (Resistance Temperature Detectors) are precision, wire-wound resistors with a known temperature resistance characteristic. In operation, the RTD is usually wired into a specific type of circuit (wheatstone bridge). The output of this circuit can be used to drive a meter which has been calibrated in temperature, or to operate a relay to sound an alarm or shut down the motor.

We use flat, molded strip type RTDs that are only .030 inch thick.

The RTDs are installed in the slot portion of form wound motors, and either in the slot (standard) or in the end turns of mush wound motors.

The RTDs used in motor windings are either 10 ohm, 100 ohm or 120 ohm. Each type of RTD has its own particular resistance characteristic. The basic detectors are listed below.

Ohms Element # of Leads
10 ohms at 25° C Copper Wire 3
100 ohms at 0° C Platinum Wire 3
120 ohms at 0° C Nickel Wire 2*

* Also available with 3 leads (must be specified at order entry).


The customer's choice of monitoring equipment dictates the type of RTD to be installed in the motor. Orders must specify the RTD resistance.

The standard RTD for U.S. MOTORS® brand products is a 120 ohm. The standard quantity is 2 per phase, for a total of six (6) RTD's. If the customer does not specify a quantity, we will supply quantity six (6).

When the customer orders bearing RTDs, usually the winding RTDs will have the same resistance value, so that the same monitoring equipment can be used.

All RTD leads are brought out to a separate outlet box with a terminal strip.