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Thread: Isolated grounds

  1. #1
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    Isolated grounds

    I was just wondering how many electricians are installing isolated ground receptacles or circuits for equipment, It seems that back in the 90's there was alot of equipment out there that was specifying an isolated circuit for there equipment, I have to say I don't do as much industrial or commercial that I used to do but I still do some and I can't remember in some time having to install an isolated ground for any equipment. I was told by a pc expert that electronics have come along way and noise in the line isn't as much of a problem as it once was. Does anyone have an opinion on this. Thanks
    (Do the job right boy or don't do it at all.)

  2. #2
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    IMO A waste of time and materials.

    Even if they where beneficial in most applications they become corrupted by incidental contact with 'non' isolated EGCs.

  3. #3
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    What Bob said.

    As an inspector, I see a lot less being spec'd on plans.
    I'm an Inspector, what do I know?

  4. #4
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    I have to admit more times then not, installations that I have come upon the ground only went to the subpanel and not back to the main, sometimes there were 2 or 3 panels in the line.
    (Do the job right boy or don't do it at all.)

  5. #5
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    I know what you mean. Some people are under the impression that the isolated receptacle itself is the only requirement. Others don't realize than NM and plastic boxes do the same thing, except for the landing-in-the-subpanel issue.

    On the other hand, we're finishing up a restaurant where IG was spec'ed for the POS terminal system and server. I used 12/3 MC and stripped the red to use as the EGC, and the green as the insulated conductor for the IG receptacles.

    Cheating? Maybe, but the inspector had no issue with it.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  6. #6
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    And if the chassis of the POS equipment contacts any stainless steel counters all your work will be for nothing....

    BTW many would say that is a 250.119 violation.

  7. #7
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    Quote Originally Posted by iwire
    IMO A waste of time and materials.

    Even if they where beneficial in most applications they become corrupted by incidental contact with 'non' isolated EGCs.
    I could not agree with this more.

    Does anyone know what the purpose of the IG is/was? I was under the impression (but do not know for sure) that back in the 70's electronic equipment used the ground in some of their communication circuits and it caused havoc when some AC equipment had some faults to ground. The IG was an effort to isolate the electronic equipment from this.

    Anyone know how/why it all got started?

  8. #8
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    Computers are still sensitive to ground "noise". The trend of less usuage of isolated receptacles is the fact that some were not installed correctly, as has been mentioned and they are easily corrupted, and they are using other technology.

    The place I see isolated circuits used most these days is for registers, by means of installing isolation transformers. I still see the lack of understanding in the field by some installers who do not quite get the concept and will inadvertently mix isolated and non-isolated circuits in some installs.
    Instructor, Industry Advocate

  9. #9
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    I'm sorry but if the electronic equipment requires the use of isolation transformers and or isolated grounds it is poorly designed equipment. This is just like the electronic people complaining that harmonics on the electrical system causes problems for their equipment...but most of the harmonics are created by their equipment. Why should the electrical system have to be changed to cover the design problems of the electronic equipment?
    Don
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  10. #10
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    An isolated ground is a good patch for bad installations. If the isolated ground is run back to main service and by-passes one or more sub-panels that have been installed with incorrrectly connected grounds and neutrals, then they may be of benefit. If the isolated ground is only run to the sub-panel, then there is no benefit. If the sub-panels are installed correctly with isolated neutrals then there is little or no additional benefit in installing isolated ground receptacles.

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