isolated ground

[tim89s]

The job specs require me to run an isolated ground from the panel to the 400 amp main disconnect which is approx 80' away. I am not to hip on running a ground through the existing energized conduit. Also I would need to change out the neutral bus in the disconnect because all the lugs are already used. Of course the neutral bus in directly behind A phase of the line. Does anyone have a good arguement I could use to avoid running the iso ground. By the way the iso ground is to be used for approx 4 cash register receptacles. Could I set an isolated ground bar in the panel and tie it to the neutral bar or would that be considered parallel paths which I know is a no no. Any ideas would be appreciated.

 

[dereckbc]

Re: isolated ground

Specifications are just that, and if you won the bid based on those specs, you are obligated to comply.

Nec does not require the IG to originate at the N-G bond point. The IG can originated there or any point down stream per code. However any other place than the N-G bond point is counter productive.

There are some alternatives like dedicated SG circuits, or the employment of an isolation transformer which work better than IG alone.

Good luck... Dereck

 

[ron]

Re: isolated ground

The best argument, if you were in a position to argue, would be that and isolated ground receptacle is generally of no benefit to the cash register.
Most of the time, you aren't in a position to argue, as the requirement is in the contract. Unless you were to offer a giant credit to the owner for not doing it.
An isolated ground is run from the separately derived source that serves that portion of the distribution. So f the panel you mention, is where the neutral to ground bond occurs, right downstream of a transformer, you would originate there as you stated, then run to an isolated ground bar (somewhat similar to the neutral bar since it is isolated from the enclosure) in the branch panelboard down stream. You wouldn't stop at a 400A disconnect, since the 20A branch circuit for the cash register receptacles wouldn't have the benefit of the isolated ground if it didn't get run to the downstream branch panelboard.

 

[steve66]

Re: isolated ground

From your description, you sound like you are planning on doing this work while everything is hot. Why not shut off the power to the panel and the disconnect first?

If the owner doesn't want to power off long enough for you to do this work, maybe that is your best argument. Insist you can't do this work without locking out the power.

Steve