Isolated Ground

[jemsvcs]

A residential client wants an isolated ground receptacle installed for his computer equipment. I plan on using 12-3 WG NMB for the dedicated circuit, with the red insulated conductor (taped green) running to the grounding bus at the service panel.

My question is this: I would consider a computer and associated equipment as being "sensitive electronic equipment." So, where is Art. 647 applicable? This particular outlet is obviously not 60V to ground (and Art. 647 is limited to commercial and industrial occupancies), but when and where is Art. 647 utilized? Has anyone dealt with this Art. before?

 

[tom baker]

Re: Isolated Ground

Art 647 is for technical power systems, it was invented in the LA area in the 80's do a goggle for balanced power systems, but its not for computer power, its used for broadcast studios.

 

[jemsvcs]

Re: Isolated Ground

Thanks a million Tom...I never would have found that one in the old Funk & Wagnall's.

 

[dereckbc]

Re: Isolated Ground

Originally posted by tom baker:
Art 647 is for technical power systems, it was invented in the LA area in the 80's do a goggle for balanced power systems, but its not for computer power, its used for broadcast studios.

Tom you are absolutely correct about the history of balanced power systems and what it was originally developed for recording-broadcast industry.

However I have designed balanced power systems for use in data centers. I had the PDU's fed from the UPS redesigned with the transformers and distribution. At first the cost seemed high until the rest of the engineers realized the cost savings from not having to build and interface to a signal reference grid (SRG), and harmonic issues were history.

jemsvcs, you mentioned a IGR in a residence. I question the use of IGR in a residence since the majority of residential branch circuits are already IGR by the construction techniques used in residential construction. I can see a dedicated circuit, but IGR

 

[scott thompson]

Re: Isolated Ground

With Romex (Type NM Cable), there already is an IG Conductor - it's wrapped in Brown Paper!
In this case, the Installation will be sufficient using a Two-Wire NM Cable - such as 12-2 w/Ground.

If there are any Metallic Boxes used in this Installation, then a separate Grounding Conductor would be needed, for this Circuit to remain an IG Circuit. That EGC would bond the Metallic Enclosures, leaving the IGC "Clean" until it terminates on the Receptacle(s).
In this case, the Installation will be warranting the usage of a Three-Wire NM Cable - such as 12-3 w/Ground.

As mentioned, an IG Circuit in a Residential location (1 Family Dwelling), is not really needed - under most circumstances, but if installed correctly it wouldn't hurt!
If your Client wants it, is willing to pay for it, and understands the needs may not warrant such a Circuit, then by all means Install it!
The Dedicated Circuit is a "Default" good idea!

Scott35