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Re: Clean Ground #97315 02/18/06 03:46 PM
Joined: Jan 2004
Posts: 1,507
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George Little Offline OP
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Quote
George this 'clean' ground still must be tired into the systems grounded conductor at some point.
What exactly is going on here?

The instllation consist of a subpanel fed with 100a conductors in a metal raceway and the contractor want's to have a "clean ground" for electronics. This ground would be connected to the Service panel and then to be used as a reference at the sub panel end. (I think) I agree that it must be tied down at the Service but it can be floating at the sub panel end as long as the raceway is being used as the EGC for the sub panel.
I think there is more to be gained by having this "clean ground" inside the raceway than having it outside the raceway aand subject to stray electrical noise in the plant.


George Little
2017 / 2014 NEC & Related Books and Study Guides
Re: Clean Ground #97316 02/18/06 04:26 PM
Joined: Jul 2001
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JBD Offline
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George, how are they going to get this single conductor into and out of the electical enclosures? Did the contractor give a reason for not runing it inside of the conduit?

Re: Clean Ground #97317 02/18/06 05:04 PM
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George Little Offline OP
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Quote
George, how are they going to get this single conductor into and out of the electical enclosures? Did the contractor give a reason for not runing it inside of the conduit?

Beats me. Another reason for putting it in the raceway with the other conductors [Linked Image]


[This message has been edited by George Little (edited 02-18-2006).]


George Little
Re: Clean Ground #97318 02/18/06 06:28 PM
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winnie Offline
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Quote

BTW one of the arguments I have heard against IG is that the "one way" penetrations through metal cabinets and raceways that are not bonded at both ends actually creates a choke that reduces the effectiveness of the IG. (similar to GECs)

If you have a single conductor in a ferromagnetic raceway, then you will get the choke effect similar to that experienced by GECs (and the reason that conduit surrounding GECs must be bonded at _both_ ends.

If the conductor is carrying fault current from the circuit conductors _in the same raceway_, then this 'choke effect' is neutralized; any current flowing in one conductor is balanced by current flowing in the other.

IMHO 'run with the circuit conductors' clearly means _inside_ of the corresponding raceway if the raceway is metallic, for the same reasons that phase conductors must not be run in separate metallic raceways.

Also, if the feeder conductors are run inside of the conduit, and the "quiet ground" run on the outside, then there will be considerable coupling between the "quiet ground" and any currents flowing on the conduit. This would seem to add noise to this quiet ground.

-Jon

Re: Clean Ground #97319 02/18/06 10:12 PM
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gfretwell Offline
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The other function of the electronic ground is to shunt high frequency transients back to ground. That will usually be a one way trip from the load end. The "choke" slows down that shot.


Greg Fretwell
Re: Clean Ground #97320 03/18/06 10:52 AM
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Paul O'Connell Offline
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George:

On the project I am on we have them both ways. Everything is a ground grid. For an Isolated ground in some instances they are installing a triad or Delta grid with insulated conductors connecting to a 1/4 in bus bar using insulated 4/0 copper and running all the isolated grounds to the bus. In other instances an Insulated 1/0 is run directly to the ground grid. EIther way all systems are connected to the grid (lightening, system, isolated grounds). WHat about ground conductors smaller than #6?

Re: Clean Ground #97321 03/18/06 12:58 PM
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renosteinke Offline
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You say this is to be run from the main to the new panel? I thought feeders always needed a ground wire, that the conduit was not sufficient. Am I wrong here?

As far as branch circuits are concerned, it was oce exlained to me that the connections on conduit just might have little sparks, wherever a connection might not be perfect- and that this would create some "noise" that sensitive electronics (such as found in a recording studio) might pick up. If there is a wire run in addition to the conduit, this issue is prevented, as the wire is a much better conductor than the pipe.

True? I don't know. The guy who was so anal about having a ground wire also had some pretty basic errors in his wiring.

Re: Clean Ground #97322 03/18/06 03:16 PM
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gfretwell Offline
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Reno the concept of the clean ground is based on the idea that a metalic raceway system may carry unwanted current from incidental things it touches along the way. An insulated wire that runs isolated from the raceway and intervening equipment/enclosures, all the way from the main grounding jumper to the equipment will not see this unwanted current (noise) but still provide a path for fault currrent.


Greg Fretwell
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