A thermal relay reports a result: the current drawn by the motor has stayed above the set value long enough. Raising the setting to silence the relay simply moves the problem into the winding. Measure first, then decide:

  1. Is the setting correct? It should equal the nameplate current, or about 0.58 times it in a star-delta panel depending on where the relay is connected.
  2. Are the three phase currents equal? If one differs clearly, look for phase unbalance, a loose connection or a missing phase.
  3. Is the voltage sufficient? Low voltage measured at the terminals under load raises current.
  4. Has the load increased? Higher flow in a pump, a fully open damper on a fan, too much material on a conveyor or a binding mechanical part pushes current above the nameplate value.
  5. When does it trip? If only at starting, the starting time is too long for the relay's trip class or the starting method does not suit the load. With frequent stops and starts, the motor accumulates extra heat with every start.
  6. Is the relay sound? If it trips while current is normal, check the relay and contactor contacts; excessive heat inside the panel also affects the relay.

If the measurements show the motor really is working above its rating, the solution is a motor of the next size up; we can choose a suitable model together from our three-phase electric motors. The article on motor failures and their causes also helps match symptoms to causes.