PlantFlow 3D › Guides › Overload relay contacts 95-96 and 97-98: test, reset and setting
Overload relay contacts 95-96 and 97-98: test, reset and setting
What the overload relay terminals 95-96 and 97-98 do, how to use the TEST and RESET buttons, manual and automatic reset, and how to set the current dial.
What a thermal overload relay does
A thermal overload relay sits between the contactor and the motor. Its three heaters carry the motor current and bend a bimetal strip as they warm up. If the motor draws more than the set current for too long, for example because the load is jammed or one phase is lost, the bimetal moves far enough to trip the relay.
The relay does not switch the motor current itself. It opens a small control contact that stops the contactor, which then disconnects the motor.
Terminals 95-96 and 97-98
95-96 is a normally closed contact. It is wired in series with the contactor coil, usually just after the control fuse or MCB. When the relay trips, 95-96 opens and the contactor drops out.
97-98 is a normally open contact. It closes when the relay trips and is used to switch an amber “overload tripped” lamp, a buzzer or a PLC input, so the operator knows why the motor stopped. The first digit 9 marks contacts that belong to a protective device.
TEST, RESET, manual and automatic reset
Most relays have a red TEST button that trips the relay by hand, so you can check that 95-96 opens and 97-98 closes without overloading the motor. The blue RESET button closes 95-96 again, but only after the bimetal has cooled, which can take a minute or more.
A selector marked H (hand) or A (auto) chooses manual or automatic reset. Manual reset is the safe default: someone must look at the machine before it can run again. Automatic reset is only used where an automatic restart cannot hurt anyone, for example in some pump controls with a separate start command.
Setting the current dial
Set the dial to the full-load current on the motor nameplate, not to the breaker size and not higher “to stop nuisance trips”. If the relay trips, find the cause: measure the current in each phase with a clamp meter, check for a lost phase, a jammed load or wrong motor connection. In star-delta starters the relay usually carries phase current, so it is set to about 58 % of the line current.
Try it yourself
Open the simulator, start the DOL motor and press the red TEST button on F1. Watch 95-96 open, the contactor drop out and 97-98 close. Then try to reset while the relay is still hot.
Open the PlantFlow 3D simulator →Safety: this guide explains principles for learning. Real installations must follow the applicable codes, the equipment manufacturer's instructions and the approval of a competent, qualified person. Isolate, lock off and prove dead before touching any circuit.