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Equipment Grounding Question

Equipment Grounding Question

Equipment Grounding Question

(OP)
I have a few skids with various motors and so forth on each.  My question is as follows:

What is best practice with regard to grounding:

Ground each item to the skid and then the skid to the ground grid...

or...

Ground each item to the ground grid itself

What are the advantages/disadvantages for each method?

Thanks in advance for your time and informed answers!

RE: Equipment Grounding Question

The most important connection is the connection of the equipment to the Equipment Grounding Conductor that is run with the power supply.  The connection to the grid itself is not a code issue, but a design issue and either method will be fine.

RE: Equipment Grounding Question

I agree with resqcapt - make sure you run a green ground wire with the power circuits (don't rely on the conduit).

If these are small motors, I think supplemental grounding to the skid is probably fine.  If these are very large motors, it is not unusual to provide a dedicated stinger to each motor from the grid. But for a ground fault in the motor, almost all of the fault current is going to flow in the equipment ground.  All other paths will have a much higher inductive reactance.

 

David Castor
www.cvoes.com

RE: Equipment Grounding Question

If this is a petrochemical plant, the API code may require grounding in addition to NEC grounding. As well as the equipment ground conductor, may require a much larger ground conductor from the motor frame to the ground grid.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Equipment Grounding Question

On oilfield power skids that we build, in addition to the line group bond, we do an exterior motor frame bond run to a ganged terminal which is mounted securely/electrically to skid frame, which in turn is wired back to service entry bond.

We've queired this requirement from our CSA inspector and they insist on it.

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