460VAC Motor Frame

[aholla8]

I am receiving conflicting opinions regarding if additional protection is needed on the motor below. These have EGCs that run with the circuit conductors from the MCCs. A QAQC is saying that NEC requirements are not met and that the motor frames are likely isolated from that steel plate due to the paint. One engineer is saying that the EGC is the only requirement, and that the motors are bonded through the bolts. Another engineer agrees with the QA saying that specific grounding bolts would need to be used.

These motors are on modules which have a bus bars that ties into the plant's ground system.

I am trying to understand this issue better. Is the frame of a motor protected via the EGC?

 

[infinity]

If the motor is isolated from the other metal than the other metal cannot be energized by the motor branch circuit so nothing beyond the EGC run with the circuit is required. If you want to bond the other metal just use a small wire bonding jumper.

 

[aholla8]

The motor frame and the flat plate it sat on has continuity, so I don't believe that it is isolated. From looking at 250.136(A), the motor is secured to and is in electrical contact with the metal structure and is connected to an EGC - it should be considered grounded.

But like you said, if it was isolated, the EGC is sufficient.

 

[infinity]

The motor frame and the flat plate it sat on has continuity, so I don't believe that it is isolated. From looking at 250.136(A), the motor is secured to and is in electrical contact with the metal structure and is connected to an EGC - it should be considered grounded.

But like you said, if it was isolated, the EGC is sufficient.

From an NEC perspective it's code compliant. It's also highly likely that the other metal in the area is already grounded to something.

 

[aholla8]

The structure does have a grounding bus bar . I am actually still concerned if it's NEC compliant. 250.136(A) points to 250.134. Is the non-current-carrying part of the motor considered to be connected to the EGC at the motor term box?

 

[ptonsparky]

Yes.