I want to run an isolated ground from a sub panel (which does not have the
ground and neutral bonded) to a receptacle for my computer. What is the
proper method. I won't be using a metal box, just a plastic old work box. I
have a book (Black and Decker Complete Guide to Home Wiring printed in 2001)
which shows 14/3 run to the circuit. It has the black to hot white to
neutral red to ground and marked as ground with green tape which hooks to
the ground bar in the panel where it is also marked with green tape. It
shows the bare ground (mind you this is just an illustration) just floating
away from the panel connected to the ground sign. The other bare ground is
just coiled up in the box. This seems strange to me and I haven't found
anything straight forward to show me exactly what to do. In the 2005
handbook I have it does show an insulated conductor that goes to the
receptacle and the panel for a ground, but they are also using a metal box
and say that the metal box and the emt or raceway must be grounded too. If I
recall all metal boxes and such must be grounded so it doesn't help me with
the plastic box.
Hope I made it clear enough.
Technically, you're not allowed to remark a 12 gauge conductor as you
describe. Why not use a metal box and MC cable which has an insulated ground
conductor. In your particular case, I don't know why 2 conductor romex
w/ground wouldn't be fine. The bare ground is isolated inside the cable and
insulated by the plastic box
I figured just plain old 12/2 on it's own circuit should suffice, but I was
stumped when I saw in that book that they used 14/3 and had the red marked
as ground and the bare ground coiled up in the plastic box. I was trying to
figure out if they were using the coiled ground to act as sort of an
antennae to attract any stray RF ore something to that effect. With that
being said, is it still a true isolated ground then if I just use 12/2 w/gnd
in a plastic box hooked to the ground bar of the subpanel? Will the bare
copper entering the subpanel after the sheathing is removed make it act like
You watch, just as soon as you finish this project, your mother board will
blow for some strange reason. I've got a pile of PC's here, all connected to
standard grounded outlets, but protected by separate UPS devices. Never had
Total waste of time and effort. Isolated grounds *may* be needed for sensitive
equipment such as certain mainframe computers, or medical equipment. There is
absolutely *no* benefit to you in having an isolated ground for a home PC.
Doug Miller (alphageek at milmac dot com)
Indeed. Besides, there's nothing "isolated" about an insulated
wire connected to the ground bus in a subpanel, neutral-bonded or
otherwise. What exactly would it be isolated from then?
The box has to be grounded in any event. Through yet another wire?
True isolated grounding systems are totally separate from regular
Except in industrial/medical circumstances, you'll probably be
making it _more_ "dangerous" (to whatever the concern is) than less.
You need nothing more than a regular grounding system and appropriate
Age and Treachery will Triumph over Youth and Skill
The theory of IG is you have a star grounded system with everything
radiating from the ground bus in the main panel where the ground
electrode connects. You are supposed to pass through all subpanels
without connecting to their ground bus.
The reality is, modern line driver/receiver practices and internal
noise rejection make it unneccessary. I think it all came about during
the learning curve of silicon IC technology.
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