Every few days, a 40 hp motor blows its overloads. These have been verified as being the correct size. The maintenance manager suspected the branch circuit breaker was faulty, so had that tested but it's fine. The motor drives a mixer tank impeller. Wet and dry materials come into the tank and mix for ten minutes. The mixed solution is sprayed onto a fixture that passes along to the next step in production. If the motor is down for long, the fixture becomes clogged. It takes a full shift to restore production.

How can you find out what’s going on?

It's unlikely the branch circuit overcurrent protection device is relevant to this problem. Focus your attention on the motor system: supply, motor, and load. First, check the voltage at the branch circuit breaker and compare that to the voltage at the motor starter. You may have a voltage drop or insulation leakage problem that is causing lower voltage and thus higher current. If that checks out, then save time with thermography.

Some things for the thermographer to check include:

  • Motor controls, especially the overload connectors and motor starter
  • All terminations between branch circuit breaker and the motor itself
  • Motor thrust bearing
  • Motor vent(s)
  • Load coupling joints and bearings
  • Gearbox

If you have an ongoing thermography program that includes imaging of these areas, the thermographer can look for changes. If not, the thermographer will need to interpret "snapshot" images to spot anomalies. Also, talk to the operators. If the dry ingredients are now being added more quickly, this could be overloading the motor.