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  1. #21
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    Quote Originally Posted by Sberry View Post
    This is a strict code violation, this recept needs a ground wire hooked to it or it needs gfci, you cannot have an outlet where a grounded tool could be plugged in without a ground. Where those are used, such as hospitals and the pipe is metal, they are mounted in metal boxes they run an insulated wire for grounding.
    Not quite...

    Isolated ground receptacles have the same 3 conductors as standard ones, but the ground conductor isn't bonded to the chassis the way a standard one is. Where the mounting ears on a standard three prong outlet are connected to the ground circuit, the isolated ground ones are not.

    So you still have the safety features of a regular outlet, but the box it's screwed into is not part of the circuit (and in this case, the table remains isolated from the circuit as well).
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  2. #22
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    What did I miss there? Yes they are not bonded, that was the point. They must have a wire hooked to them if they are not on gfci which is the only exception for allowing a 3 wire recept to a 2 wire supply. Basically you cannot have an ungrounded 3 wire outlet.
    I use the hospital example because its the most common use for them, piping and raceway is all bonded.
    Here is another scenario, computer circuits in homes, often they call for special grounding. The simple way is to run a romex from the MAIN panel and mount in a plastic box, makes for insulated (or isolated) ground.
    Last edited by Sberry; 11-04-2008 at 07:54 AM.

  3. #23
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    I think you're mistaking terminology here. Duplex receptacles are double outlets, not two prong receptacles.

    The ground wire from the center prong is still part of the electrical circuit, but not bonded to the chassis of the mounting enclosure. That's why it's an "isolated ground" - normally, the ground would be bonded to the enclosure for protection from stray current of a live wire coming in contact with it. That path creates issues with the GFCI's because stray current can then pass from another circuit (the welder, in this case) through the tables frame back to ground and trip the protection.

    The isolated ground circuit you refer to in audio, computer, and hospitals is an entirely different beast. There, what you're doing is preventing paths through multiple ground circuits by wiring them in such a way as to prevent ground loops (which is what actually causes the GFCI issues with the bonded table scenario). The reason to isolate grounds with electrical components has to do with induced noise where the ground circuit is used as a base line for determining voltage across the signal conductors. You end up with a current flowing across the grounds at the power supply's alternating frequency (60hz) which induces noise in the signal due to the base voltage (which is supposed to be zero) carrying current before reaching true ground.
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  4. #24
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    I think you're mistaking terminology here. Duplex receptacles are double outlets, not two prong receptacles.

    The ground wire from the center prong is still part of the electrical circuit, but not bonded to the chassis of the mounting enclosure. That's why it's an "isolated ground" - normally, the ground would be bonded to the enclosure for protection from stray current of a live wire coming in contact with it. That path creates issues with the GFCI's because stray current can then pass from another circuit (the welder, in this case) through the tables frame back to ground and trip the protection.
    I am not mistaking anything here, I am familiar with a duplex, what I am saying is that you cannot use a iso duplex without hooking up the ground wire, just making that clear. If you dont intend to bond this to the table then that is the outlet to use for the reasons you point out, its not bonded to the enclosure. Now as for the gfci, no connection between the gfci part of the unit and its grounding terminal. The ground pin is the same as any other 3 wire duplex, a mechanical/electrical connection.
    I realize this conversation got mixed up, I now realize what Cruizer was saying, just to use the outlet, he didn't mean to feed it 2 wire but to use the 3rd.

  5. #25
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    You are permitted to replace a two-wire nongrounding type receptacle with a GFCI under the following in section 406.3 (3) Nongrounding-Type Receptacles. Where grounding means does not exist in the receptacle enclosure, the installation shall comply with (a), (b), or (c). (a) A nongrounding-type receptacle(s) shall be permitted to be replaced with another nongrounding-type receptacle(s). (b) A nongrounding-type receptacle(s) shall be permitted to be replaced with a ground-fault circuit interrupter-type of receptacle(s). These receptacles shall be marked "No Equipment Ground." An equipment grounding conductor shall not be connected from the ground-fault circuit-interrupter-type receptacle to any outlet supplied from the ground-fault circuit-interrupter receptacle. (c) A nongrounding-type receptacle(s) shall be permitted to be replaced with a grounding-type receptacle(s) where supplied through a ground-fault circuit interrupter. Grounding-type receptacles supplied through the ground-fault circuit interrupter shall be marked "GFCI Protected" and "No Equipment Ground." An equipment grounding conductor shall not be connected between the grounding-type receptacles.
    Just a portion of it worth repeating.

  6. #26
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    The isolated ground duplex, has a ground wire attached to it. that ground wire that comes off the isolated duplex is merely going to another ground point elsewhere.

    Like in our remotes, be it a Classic 300D, Miller or other Lincoln with AC receptacles. I don't like to have our remote boxes live via a neutrally bonded welder, so we use isolated duplexes on the remote to isolated the grounds at the source. In this case your moving the ground away from the table to a another less hazardous point be it a regular receptacle, GFI or direct to a breaker panel.
    Presto no problems.

    I suppose you could use a GFI connected to the table, however if he does have a bad work clamp, your still going to smoke both the GFI and lines leading to it.

    I got this idea origiinally from looking at a hospital plug, now it is the norm for every remote builder, I know of for operator saftey. I even reverse them like the hospitals as the plugs don't fall out of the receptacle.
    Last edited by cruizer; 11-04-2008 at 03:10 PM.

  7. #27
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    I've installed isolated ground receptacles in hospitals and computer stations. They needed four wires. The hot, the neutral, the isolated ground, and the normal ground. The isolated ground went from the pin (not bonded to the frame) directly to the panel without connecting to the other grounds, but the normal ground was bonded to all metal boxes and conduits along the way.

  8. #28
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    As a Ham Radio idiot , I might be wrong here because no one has said what I'm thinking.

    Isn't ground, simply ground? Whether 110vac ground or 220vac ground (both the green wire) which ultimately connects to earth ground as well as chassis (welding table) ground. The welder's ground is also a "chassis" ground. I guess I'm missing something - I don't see the problem?

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  9. #29
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    Yes, the welder has a chassis ground, the concern is being able to pass welding current thru the building wiring (chassis ground) There are a couple possible scenarios but in the case of the original poster its highly unlikely.
    Here is a case though, say you have a metal welder cart and the work lead from the machine is laying on it, you forget to hook it to a grounded bench, or even a grounded power tool could be laying on a metal bench, strike arc on this bench and it will take the path thru the cords back to work lead laying on the cart.
    I usually clip the work lead (welding ground) to a plastic hanger on the machine cart once it leaves the bench.

  10. #30
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    This is a good case for using some correct terminology, earth ground for this purpose is confusing, we should be saying equipment ground.

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