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 Protective Earths, the forgotten conductor

Protective Earths, the forgotten conductor

Monday, June 15, 2020

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 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. 3Phi-Reliability.com

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