riverjig87
Member
- Location
- Minot, North Dakota, USA
Ok. I have searched very persistently through multiple threads touching on this subject. I will use a general example. We are at a mine where they require all motors to not only have an EGC but also an external ground bonded to the frame of the motor(which in essence is an EGC). Now, per NEC 430.242, "The frames of stationary motors shall be grounded under the following conditions:
(1) Where supplied by metal-enclosed wiring
(2) Where in a wet location and not isolated or guarded
(3) If in a hazardous (classified) location
(4) If the motor operates with any terminal at over 150
volts to ground
Where the frame of the motor is not grounded, it shall
be permanently and effectively insulated from the ground."
This motor in question meets requirements 2,3,4.
Ok The argument is the method. I am stating that 250.122 is what you would use to externally bond this motor being that it is being used for the supply conductors and EGC ran with the feeders for this motor. There is no reason to install any larger bond wire being as there is only so much available current for a fault.
So the question is this: Do you size the external motor frame grounding conductor using 250.122?
What some contractors have been doing is installing this external case ground to a ground ring or to building steel which is also grounded to this same ground ring. In my opinion, I now see case for difference in potential if a fault occurs. But this isnt the issue.
I do not see a clear explicit explanation for this thru-out the code. Any further clarification to this matter would be greatly appreciated.
(1) Where supplied by metal-enclosed wiring
(2) Where in a wet location and not isolated or guarded
(3) If in a hazardous (classified) location
(4) If the motor operates with any terminal at over 150
volts to ground
Where the frame of the motor is not grounded, it shall
be permanently and effectively insulated from the ground."
This motor in question meets requirements 2,3,4.
Ok The argument is the method. I am stating that 250.122 is what you would use to externally bond this motor being that it is being used for the supply conductors and EGC ran with the feeders for this motor. There is no reason to install any larger bond wire being as there is only so much available current for a fault.
So the question is this: Do you size the external motor frame grounding conductor using 250.122?
What some contractors have been doing is installing this external case ground to a ground ring or to building steel which is also grounded to this same ground ring. In my opinion, I now see case for difference in potential if a fault occurs. But this isnt the issue.
I do not see a clear explicit explanation for this thru-out the code. Any further clarification to this matter would be greatly appreciated.
