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?
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.
Re: isloated ground receps in plastic boxes#40344 07/18/0406:18 AM07/18/0406:18 AM
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.
Re: isloated ground receps in plastic boxes#40345 07/18/0407:56 AM07/18/0407:56 AM
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.
Re: isloated ground receps in plastic boxes#40347 07/18/0408:43 AM07/18/0408:43 AM
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 Massachusetts
Re: isloated ground receps in plastic boxes#40348 07/18/0408:43 AM07/18/0408:43 AM
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.
Re: isloated ground receps in plastic boxes#40349 07/18/0409:46 AM07/18/0409:46 AM
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??