PRODUCT OPTION: PT100 Temperature Sensors

Lately, more and more of our readers have been inquiring about RTDs, or resistance temperature detectors. A common type of RTD is the PT100. This type of device has begun appearing more frequently on bid specifications and product requirements, and as a result, our Submersible Service Hotline has seen a surge of requests for information. What is it? What does it do? Does Franklin Electric supply it? To get the word out most effectively, we are therefore giving this topic special attention in this issue of Franklin AID.

Simply put, the PT100 is a platinum wire precision resistor that is placed in a special stud bolt for the Franklin Electric motor. Separate control leads must then run to a surface control unit to monitor temperature. The PT100 can then be used to detect insufficient cooling to the motor and thus contribute to its protection. Note, however, that this sensor does not replace the required electrical overload protection that is specified in the motor installation manual. All three power supply legs of a three-phase submersible motor still require an ambient compensated overload with quick-trip characteristics (NEMA Class 10) or a Franklin Electric Subtrol-Plus premium motor protection system.

PT100 sensor retrofit kits with instructions for easy field installation are available from Franklin Electric for 6″, 8″, and Severe Duty motors. In addition, Severe Duty motors can be ordered with the PT100 sensor already installed. The surface control unit, however, is not available from Franklin Electric but can be purchased through most outlets for electrical controls. For your convenience, part numbers and specifications for the PT100 sensors available from Franklin are listed below.

 PT100 Installation To install the sensor bolt, remove the top end bell bolt that is opposite the lead and replace it with the PT100 sensor. Do not loosen or remove the other three bolts in the end bell. Tighten the sensor bolt to the torque specifications listed below.

Surface Control Unit As noted earlier, surface control monitoring units are not available from Franklin Electric and must be purchased separately. When programming these units with respect to a Franklin submersible motor, however, Franklin does require the trip settings be programmed as listed in the table below.

 Additional information about PT100 temperature sensors is available by calling our Submersible Service Hotline at 800-348-2420. You may also submit questions via e-mail to You may also see the North American Field Service Engineers.