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Thread: Anyone use Isolated Ground receptacles for office or school's?

  1. #11
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    Quote Originally Posted by zbang View Post
    Still a waste of money IMHO. Even in shielded cables the signal wires are balanced differential pairs and isolated at each end, you might get some current flowing over the shield, but very unlikely to affect the data.
    Never looked at how modern equipment that uses STP cable is designed, but I'm sure the designers took the possibility of ground loops into account. Possibly lifted at one end or capacitively isolated.

    -Hal

  2. #12
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    The last two or three IG installs I did were for restaurant kitchen-order/POS systems. Interesting because just about every component had low-voltage power supplies and used CAT-5 cabling, making the IG a futile gesture IMHO.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  3. #13
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    Quote Originally Posted by hbiss View Post



    The only way you are going to have objectionable current flowing (ground loop) is when the equipment has another path back to ground that's different from the receptacle ground it receives power from.

    -Hal
    Hi Hal,
    As to your well made observation:
    "The only way you are going to have objectionable current flowing (ground loop) is when the equipment has another path back to ground that's different from the receptacle ground it receives power from."
    You are of course correct- and that is the only scenario where this applies. But for application's sake and example: My computer tower on the floor under my desk right now, is in a metal casing. Albeit cheap and thin, the metal casing is still of course a conductor. The third wire in the computer's cord (grounding conductor in the computer tower's 3-prong appliance cord) is clipped/soldered to the interior side of that metal computer casing. If I set the computer tower/casing against the exposed 1/2" copper water cut-off plumbing piping in the corner of my office, and the baked on paint on the computer casing exterior doesn't act as an insulator against the objectionable current on my grounding system of my electrical system (which I have in this 85 year old leased-office) then the objectionable current could loop right back to the water piping, building a field (induction) around the computer tower and its internal(s) the entire time. The Isolated Grounding conductor- when insulated and unspliced as it should be when installed, would carry it so far away from this alternate path at the grounded copper pipe, that the Obj. Current surely would choose the MBJ connected to the service neutral, and then exit the premises wiring, vs coming back my way to complete its path to ground.
    Not a typical situation of course, and more the exception than norm (therefore not very practical) but just an observation after reading the material.
    Long time forum reader, and first time post(er). I've enjoyed this forum for nearly two decades (seems that long anyway). Thank you very much for having me.
    Thanks!
    Jerry

  4. #14
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    Quote Originally Posted by JLDURHAM View Post
    . On top of that, this Isolated Ground Conductor is required to stay remote (disconnected) from all other grounding splices within the grounding system, until it reaches its target: the EGC terminal bar inside of the panel.
    While that is optimal, the NEC does not require the IGC to go all the way to the EGC terminal bar. 250.146(D) states the IGC "shall be permitted" to run the panelboard...with out connection to boxes, etc.

    So you could terminate the IGC at the box where the receptacle is installed.
    Where I have seen the IG receptacles used successfully is in audio sound systems.
    Moderator-Washington State
    Ancora Imparo

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    Quote Originally Posted by tom baker View Post
    While that is optimal, the NEC does not require the IGC to go all the way to the EGC terminal bar. 250.146(D) states the IGC "shall be permitted" to run the panelboard...with out connection to boxes, etc.

    So you could terminate the IGC at the box where the receptacle is installed.
    Where I have seen the IG receptacles used successfully is in audio sound systems.
    Thank you; yes.
    "Required" to be disconnected from the grounding system by default of function, (if actually a functional "isolated" ground) but not required by the NEC.

  6. #16
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    Quote Originally Posted by JLDURHAM View Post
    Hi Hal,
    But for application's sake and example: My computer tower on the floor under my desk right now, is in a metal casing. Albeit cheap and thin, the metal casing is still of course a conductor. The third wire in the computer's cord (grounding conductor in the computer tower's 3-prong appliance cord) is clipped/soldered to the interior side of that metal computer casing. If I set the computer tower/casing against the exposed 1/2" copper water cut-off plumbing piping in the corner of my office, and the baked on paint on the computer casing exterior doesn't act as an insulator against the objectionable current on my grounding system of my electrical system (which I have in this 85 year old leased-office) then the objectionable current could loop right back to the water piping, building a field (induction) around the computer tower and its internal(s) the entire time. The Isolated Grounding conductor- when insulated and unspliced as it should be when installed, would carry it so far away from this alternate path at the grounded copper pipe, that the Obj. Current surely would choose the MBJ connected to the service neutral, and then exit the premises wiring, vs coming back my way to complete its path to ground.
    Yeah, and aliens could come in a zap it with their EMP ray too. I think it's much more likely that you will spill coffee all over your keyboard than something like that causing a problem.

    -Hal

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