Earthing on the Motor Frame(IEC 60034-1)

[shkim2000]

I have read IEC 60034-1 in conjuction with motor earthing. It tells me to be earthed from motor frame in addition to earth tap on the terminal box for motor more than 100kW.
If the bonding is achieved between motor frame and terminal box, the motor frame is still required ?
Can you tell me technical backgound/reason in requiring motor frame earth ? My situation is that only terminal box earth is beneficial for us.

 

[Sparkey5774]

A lot will depend on your application. In some instances earthing the motor frame can help to reduce EMI noise generated by the motor. This most will effect the equipment around the motor and not necesarily the motor itself. Also, earthing the frame is mainly done for safety reasons. In fault situations, if the frame of the motor is ever to become live, the earthing should cause the breakers/fuses to trip thus preventing any prolonged safety hazard to those who may come in contact with the motor frame. Although I am not directly familiar with IEC 60034-1, I would imagine that both the terminal earthing and the frame earthing are required for additional safety due to the larger powered motor you are using.

 

[aolalde]

Grounding (earthing) of the frame is required for personnel safety reasons. If an eventual insulation failure should happen the voltage from the frame to ground is not allowed to build up.If the conduit box is grounded properly, connect the frame to ground with an internal jumper from the box to the frame.

 

[waross]

In some plants, oil refineries come to mind, the frame ground is a redundant safety feature. At one site, the frame grounds were seperate from the junction box ground which ran with the motor circuit conductors.
The ground connection inside the terminal box satisfied the NEC or CEC.
Other codes or policies mandated the external frame ground.
One advantage of the external ground connection is that it is readily visible and plant operators can see and report any disconnections or damage.
respectfully

 

[ozmosis]

Connecting a voltage to a motor is not just possible via the motor power terminals, it is possible to have separately powered brakes, fans, etc and having an additional motor frame ground is another means to ensure that any possibility of the earth being missed for other devices is thus eliminated.