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Joined: Jun 2004
Posts: 220
Has anyone used IG receps in plastic boxes. 12-3 NM-B for a wiring method. My question is, how do you ground the yoke of the recep with the EGC? there is only 1 screw on the recep? Do they make an IG with 2 screw?

Joined: Mar 2002
Posts: 86
Good question, the only thing that I would suggest is to install a metal box. Unless it's already to late.

Joined: Apr 2002
Posts: 558
If you are using a non metallic box there is no reason to use an IG receptacle. What is this IG receptacle going to be used for?


Curt Swartz
Joined: May 2001
Posts: 378
What would the rules be on that? I mean if the box has no ground and the iso ground runs back to the isolated buss in the panel with isolated cable using the insolated ground conductor would it pass? Also since an IG receptacle has the ground pin isolated from the rest of the receptacles some metal parts such as the tang would not be grounded as the screw grounds the the tang to the service grounded metal box. You can't use a bare ground in either BX or NM because it would compromise the system if it touches the panel box or metal sheath. The panel should have two grounding buss bars and one being isolated if anywhere in the wiring the grounds touch it's not isolated. If its L.I.M system however they can be joined and IG receptacles are not used. I once asked two different inspectors the same type of question and got two different answers. Best to call inspector who will be involved.Never seen an IG with two grounds but who knows.

Joined: Dec 2003
Posts: 751
While the NEC has rules on the correct installation of an isolated ground, it never requires one. The NEC also never really says haw far back the isolation has to go; to the panel?; to the separately derived system?; to the service? These are questions that are left to the engineer to specify.
In the case of a non-metallic enclosure for a isolated ground receptacle, there must be a means of bonding the yoke provided. If the receptacle cannot be found that has two ground screws, then the box must provide the bond. There are plastic boxes manufactured that do provide a means of bonding the yoke via metallic screw inserts bonded internally to a grounding screw inside the box.
Like everything else, we have to install the right box for the application.

Joined: May 2002
Posts: 1,716
In this case a standard receptacle would achieve the same results as an isolated ground receptacle, and at the same time bond the yoke with no adverse affects.

As Curt said, there is no reason to install an isolated ground receptacle in a non metallic wiring method or enclosure.

As far as using plastic boxes in a "Line Isolation Monitored" (in a hospital) system, this would be a violation of 517.13, although isolated ground receptacles are allowed in 517.16.


[This message has been edited by Roger (edited 07-18-2004).]

Joined: Jun 2004
Posts: 220
the receps are for computer equipment in a rewire of an existing bank. Specs call for IG receps. Building is all wood construction, using 12-3 NM for the IG. Another question I have, can you put more than 1 recep on 1 circuit? wouldn't this cause "noise" on that circuit if two computers where on the same circiut? Thanks for the answers so far.

Joined: Jan 2003
Posts: 4,391
The use of IGs at all is controversial at best.

To do it the 'best way' no you may not have more than one outlet per IG conductor and that conductor has to go all the way back to the point that the electrical system is bonded.

Most times I do not see it done this way, at best there will be separate IGs back to the first panel where an IG terminal bar will be installed and from that point a single conductor is run back to the bonding point.

Do it however your job specifications allow, however I agree with Roger and Curt an IG outlet in a plastic box in a wood frame building does nothing that a standard outlet will do.

To satisfy the job requirements go ahead and put the IGs in but you will have to use a metal box or the special plastic bonding boxes as has already been said.

Strictly speaking you can not use 12/3 for this, remarking the red for use as the IG is a violation.


[This message has been edited by iwire (edited 07-18-2004).]

Bob Badger
Construction & Maintenance Electrician
Joined: Feb 2004
Posts: 74
CRM Offline
Let me just say that isolated ground receptacles are the biggest scam on the market. They will do absolutely nothing about protecting computers from surges or other problems. A UPS power supply is the way to go. Having said all that a lot of specs call for them. Generally we put 4 IG receptacles on a isolated ground circuit. If possible I would also recommend a metal box instead of plastic.

Joined: Jun 2004
Posts: 220
I didn't think the 12/3 was an issue, but I see now the code section involved,250-119(b). It just doesn't make sense to me, I mean I can put purple tape on a white wire to reidentify it for ungrounded use. I can put white tape on a black wire to reidentify it for nuetral use, but I can't put green tape on a red wire to identify it for grounding use?? Does anyone know why this is??

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