JR28 Thermal Overload Relay for Motor Protection in Contactor Panels
The JR28 is a thermal overload relay that plugs onto the load side of a contactor and opens the control circuit when a motor draws too much current for too long. Three frames cover the range, JR28-D13, JR28-D23 and JR28-D33.
Three Frames for Three Contactor Sizes
Frame width runs 46mm on the D13, 56mm on the D23 and 72mm on the D33, with body length from 94mm to 117mm, so the relay stays inside the footprint of the contactor it is fitted to. Choose the frame by contactor rating, then set the dial to the motor full load current.
Trip Points on the Curve
The dial scale is printed on the face of each frame. At 1.05 times the setting the relay carries current for more than two hours, which leaves room for a motor running slightly above nameplate. At 1.2 times it trips inside two hours from the hot state, at 1.5 times inside two minutes, and at 7.2 times it opens between 2 and 10 seconds, so a stalled motor is cleared before the winding cooks. A red STOP button drops the circuit by hand and the blue RESET button clears the trip.
Phase Failure Protection
Losing one phase is the fault that kills small motors, because the remaining two pull more current while the shaft keeps turning. With any two phases at 1.0 times the setting and the third at 0.9 times, the relay holds beyond two hours from cold. A dead phase with the other two at 1.15 times trips inside two hours from the hot state, so the contactor drops before the winding reaches its limit.
Contacts, Mounting and Wiring
One NO and one NC contact are wired to 95-96 and 97-98, and the closed contact sits in series with the contactor coil so an overload drops the motor even if the start button is still held. Three pins on the top of the relay plug into the contactor load terminals, and the motor cable lands on 2/T1, 4/T2 and 6/T3. Send your motor full load current, contactor model and quantity to WTAIELE for a quote.
