Motor Earthing

On all electric motors I have installed in UAE, KSA & Oman, it was required that the motors have internal earthing back to the control panel, and external earthing of the motor case to a permanent earthing boss on the metal frame. The permanent earthing boss was in turn connected to earth.

The body of the motor should be connected to earth .Ushually 2 independent earth connection from the body and one from terminal box is the practice in India.Two earth connections is the normal practice.

Yes it is required to connect an earth conductor(wire) from the metal frame to the main earth which leads to the general mass of the earth. This will enhance effective earthing(protective multiple earthing).

The purpose of a metal frame is not "solely" for earthing the motor. The resistance offered by the metal frame would depned on the contact resitances too, which would normally be higher. SO, to provide for a low resistance, definite-purpose earth fault current return path, one needs to provide a seperate protective conductor from the motor frame to the earthing conductor, whose only purpose is to provide a low resistance path for the earth fault current to return to the source.

What will it take to run an earth continuity conductor to the motor. It is necessary to provide the motor with a separate earthing to ensure a confined earth fault path and adeduate size earth continuity conductor. The metal fram can be used but remember it not a good conductor and a lot of other units are or may be seated on same fram. DICKSON.

Follow the local equivalent of British Standard 7671.