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89T Series Combination Control for Electric Water HeatersThe 89T series controls are designed to meet the high electrical loads and long life requirements of electric water heaters. The 89T combines the temperature control and temperature limit thermostats into a single housing with a small footprint and low profile. Both switches use a temperature sensitive bimetal disc to provide high-speed, snap-action contact separation for a long, dependable life.Features and Benefits The 89T series features include:An automatic reset control which is adjustable over a 60℉(33℃) range. The lowest adjustable limit is 90℉ (32℃). The highest adjustable limit is 200℉ (93℃).A manual reset control which operates at a factory calibrated temperature and may be specified between 160℉ (71℃) and 220℉ (104℃).The 89T mounting tabs snap into the customer’s bracket to mount the thermostat to the water tank. The 89T is interchangeable with brackets used on the Therm-O-Disc 59T/66T controls.Switch ActionsThe automatic reset control portion of the 89T is available in two switch actions:Automatic reset SPST — The switch opens the normally closed contacts on temperature rise. The contacts automatically return to the closed position when temperatures return to the reset point.Automatic reset SPDT — This operation is the same as the SPST with the addition of an auxiliary set of contacts, which make circuit upon opening of the normally closed contacts and breaks this circuit upon automatic reset.The manual reset limit control portion of the 89T is only available as an open-on-rise DPST switch. The contacts return to the closed position when the reset button is pressed after the control has cooled below the open temperature. This construction is classified as “M1 Trip Free” by UL and CSA. The manual reset control may automatically reclose at temperatures below 32℉ (0℃).Typical ApplicationThe thermostats and wiring diagram shows a typical electrical water heater with two heating elements for non-simultaneous operation.The 89T SPDT temperature control switches power from the upper heating element to the lower element when its calibration temperature is reached. The lower element electrical control is a 59T SPST thermostat. The 89T DPST temperature limit provides a full power disconnect through both power conductors in the event of an overheat condition. Pressing the manual reset button will reclose the contacts and restore operation.The thermostat and wiring diagram is for 240VAC single element water heaters and commercial water heaters where each heating element is independently controlled. The automatic reset SPST control provides power to the heating element to regulate temperature. The DPST manual reset limit control provides full power disconnect in the event of an overheat condition.Therm-O-Disc Incorporated was founded in Mansfield, Ohio in 1947. Today, as a subsidiary of Emerson and a part of Emerson Appliance Solutions and Emerson Climate Technologies, the company is recognized world leader in design and manufacture of temperature sensors and controls for the HVAC, appliance, automotive and electronics industries.
