A motor circuit can suffer a ground fault from a bearing failure, Rotor rub, Variable Speed Drive attack, or Winding fault.
So what happens if a high resistance earth exists when one of these faults occurs.
The risk is the fault current finds its lowest resistance path, this can be a person, cable tray full of dust/powder, adjacent machinery, or ceiling cavity.
The probability of failure is relatively high unless a Motor Management Strategy has been implemented, and the Risk Loss is high.
Personal injury, Fire and Machinery damage are likely.
In this photo the rear motor has a protective earth, the motor in the foreground has none. It has been completely forgotten.
This photo shows the electrical panel earth Hmmm! Several bad practices has occurred, the lug has a nut in the current path, its corroded, and the added plate bolted to the frame. In this case the lug has been place onto a painted surface, and left to corrode.
Corroded unlugged motor terminal has a high resistance joint.
A Motor Health Assessment by www.3Phi-Reliability.com/services includes protective earth testing and inspections. Reduce your insurance risk, protect people, and be assured your motors have a working earth.
Motor Health Assessments follow the IEEE1415-2006 standard for Maintenance & Failure Analysis of inductive equipment.