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Thread: Triad grounding

  1. #1
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    Jul 2008
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    Triad grounding

    good day.

    i am trying to understand the principle or theory behind triad grounding. i am search the net but nothing as yet. any one with information or have used triad grounding could you please shed some light.

  2. #2
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    I see it on drawings and have installed it many times, but never knew why.
    It's not a code requirement. It's some old school design that has lived on over the years, I think.
    Tim
    Master Electrician
    New England
    Yesterday's Technology at Tomorrow's Prices

    Answers based on 2011 NEC

  3. #3
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    Please educate this poor soul. What is "triad grounding"?

    cf

  4. #4
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    Installing 3 ground rods in a triangular formation. I think?

  5. #5
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    Seems like I've even seen that spec for "isolated grounds", which I never follow since it's a code violation. They want the "isolated ground" so isolated that it goes to its own set of rods that will do absolutely nothing. Seems like the "triad ground" is often spec'd to be a triangle with 10 foot sides, with a rod driven at each corner.

  6. #6
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    funny this was brought up, I installed a 600A service where the ground rods were the main ground (no water ground), the inspector wanted (3) 3/4 x 10' grods in a tri 6' apart, w/ a full size ground going to them. Didn't know where he came up with that tri

  7. #7
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    I have asked a few designers why they want this and some of the answers have been "for better breaker operation", "I don't want the customer to have a lot of noise on their electronic equipment", "personnel safety".

    I think the translation of those answers were, "I don't know".

    Roger
    Moderator

  8. #8
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    Quote Originally Posted by roger
    I have asked a few designers why they want this and some of the answers have been "for better breaker operation"......., "personnel safety".
    Those are some scary answers. These people shouldn't be designing electrical systems if they think grounding electrodes have anything to do with OCPD operation.
    John from Baltimore
    "One Day at a Time"
    Responses based on the 2008 NEC

    If you can stay calm, while all around you is chaos...then you probably haven't completely understood the seriousness of the situation

  9. #9
    Join Date
    Jul 2007
    Posts
    8

    Triad Grounding

    Hello to all,

    Triad grounding is important in order to facilitate periodic testing of the effective grounding system. Three rods are buried and connected with insulated cable (probably 90 mm), ofcourse the insulation of that part of the cable which is bolted to the rod is removed. Test pits allowing access to the top of each rod.
    In order to effectively test the ground resistance the rest of the grounding system must be disconnected from the rod, if only a single rod was buried then for the duration of the test the system would be ungrounded which is extremely dangerous, the three rods and their interconnections allow this testing to occur and also eliminate the need for a test rod to be driven as 2 out of the 3 rods can be disconnected and the earth resistance test done while the third rod maintains an effective ground. The distance between the rods is usually equal to or a bit more than the length of the rod in order to avoid interference and thus provide a true measurement of the earth resistance at that point. This system also facilitates redundancy and increased availability of the grounding system and is used mainly for grounding of instrumentation and computerized systems and so is isolated (except for a single bond) from the plant (dirty) earthing network which may be buried bare copper, rods and building rebar etc.

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