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Thread: Best Grounding for 200a panel.

  1. #1
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    Best Grounding for 200a panel.

    Hello all.

    I am installing a 200a 3ph sub panel in a venue to power audio amplifiers. This audio equipment will have it's own isolated ground. The client said he want's 3 grounding rods. Is there any reson 3 rods will serve better than two?

    thx

  2. #2
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    The number of ground rods won't matter much. Is this in a separate structure? And how do you intend to connect the IG to the system? You cannot connect it solely to the ground rods.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  3. #3
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    Quote Originally Posted by markebenson View Post
    Hello all.

    I am installing a 200a 3ph sub panel in a venue to power audio amplifiers. This audio equipment will have it's own isolated ground. The client said he want's 3 grounding rods. Is there any reson 3 rods will serve better than two?

    thx
    Not really. ‘Triad grounding’ (i.e. 3 triangulated ground rods separated by 10 feet) is not a code requirement but more of a common practice for some industries. The intent typically is to reduce ‘noise’ or EMI, i.e. ‘electromagnetic interference’ within control systems circuity such as analog, communications etc. One of the buried rods is usually designated as a grounding test well, which allows periodic testing of the system for resistance – the lower the ohms, the better. You’ll have to bond the Isolated Grounding system to the ‘dirty’ or safety grounding system in at least one point – and this is a code requirement.

  4. #4
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    As the others have mentioned, the new ground rods from this new sub-panel will still have to be connected to the existing grounding electrode system. Isolated equipment grounding does not mean isolated earthing.

    Roger
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  5. #5
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    Quote Originally Posted by markebenson View Post
    This audio equipment will have it's own isolated ground. The client said he want's 3 grounding rods. Is there any reason 3 rods will serve better than two?
    You can charge extra for installing it.

    Is this for temporary or permanent audio systems? With the latter, they have a prayer of it staying isolated for at least a few weeks; with the former each event is a toss-up.

    If you search these forums, you find that most people here don't have a high opinion of IG systems.

  6. #6
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    Let me explain further. The Isolated portion is intended for a couple 4 wire 50 amp distro outlets for the stage. The band will connect their portable distribution panel to these outlets. The objective is absolutely to reduce noise. There are many old school bands that will be using old style transformer based ampliers for sound.

    So to redirect, would there be a way to completely isolate these (2) 50 amp 4 wire outlets from the "dirty" system and if not will would a still be a benefit to using seperate ground rods.

  7. #7
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    Quote Originally Posted by markebenson View Post
    Let me explain further. The Isolated portion is intended for a couple 4 wire 50 amp distro outlets for the stage. The band will connect their portable distribution panel to these outlets. The objective is absolutely to reduce noise. There are many old school bands that will be using old style transformer based ampliers for sound.

    So to redirect, would there be a way to completely isolate these (2) 50 amp 4 wire outlets from the "dirty" system and if not will would a still be a benefit to using seperate ground rods.
    The bottom line is the grounding has to all be connected period, no compromise.

    Forget the ground rods and run a isolated EGC straight to the first point of service, that's all you can do legally.

    You do understand that the earth does not clear a fault or provide personnel protection at the voltages you are working with don't you?

    Roger
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  8. #8
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    If you're thinking that somehow ground rods are the solution to a potential noise problem you're incorrect. It's dangerous and because of that connecting solely to the rods is not permitted by the NEC. The EGC from your 50 amp receptacles must be connected to the system EGC. As Roger suggested the best you can do is run an IG back to the service or if there is one a transformer X0 connection.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  9. #9
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    Quote Originally Posted by markebenson View Post
    So to redirect, would there be a way to completely isolate these (2) 50 amp 4 wire outlets from the "dirty" system and if not will would a still be a benefit to using seperate ground rods.
    Sure, install a transformer and supply the outlets from a separately-derived-system; that'll isolate the power leads from the "dirty" power system. No matter what you do, the outlets' grounding conductor has to run back to the system bonding jumper and to the grounding electrode system; and if you add a second set of ground rods, those must connect back to the main set (it's all in Art. 250). You have to provide a path for fault current and also to the GES.

    What the client is looking for is an audiophile-induced snake oil solution. If you want to really get into the weeds, technically, take a look at http://web.mit.edu/jhawk/tmp/p/EST01...ps_handout.pdf, the author knows his business.

  10. #10
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    Here's another interesting write-up on isolated grounding systems:
    http://www.ecmweb.com/nec/sensitive-electronic-grounding-industrial-locations

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