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Trenched ground rod
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Trenched ground rod

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Trenched ground rod
Residential Wiring - The Right Way!

Wiring Information for the Do It Yourself Homeowner

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Thread: Trenched ground rod

  1. #1
    Join Date
    Feb 2012
    Location
    Lala land, OH
    Posts
    235

    Default Trenched ground rod

    I have shallow bedrock and no choice but to dig a trench for my ground rod and lay it flat. Is there any requirement for the ground clamp location? Can I put the clamp in the middle of the rod? I saw no mention in the NEC about it.

  2. #2
    Join Date
    Feb 2012
    Location
    Kent, WA
    Posts
    216

    Default

    Anywhere on the electrode is fine -- one end, other end, middle...
    Mark
    Kent, WA

  3. #3
    Join Date
    Feb 2012
    Location
    Welland Ontario
    Posts
    398

    Default

    Can you use a ground plate in USA? Much less digging and becoming more common up here.

    Trenched ground rod-8807639285790-jpg
    Operation Overlord.

  4. #4
    Join Date
    Feb 2012
    Location
    Kent, WA
    Posts
    216

    Default

    Yes. They are treated like rods and pipe electrodes (e.g. general category of Made Electrode). Plate electrodes shall be installed not
    less than 750 mm (30 in.) below the surface of the earth.
    Mark
    Kent, WA

  5. #5
    Join Date
    Feb 2012
    Location
    Lala land, OH
    Posts
    235

    Default

    I thought about it but I dont have the room (width) for one before crossing over to my (bitchy) neighbors yard. Only have about 2.5 or so feet over there and my sewer line somewhere too.

    I only have 2 feet of dirt till bedrock with less in other areas. The inspector gave me permission to bury the rod a inch or 2 above the bedrock.

    On a related note.. My cable box is right next to my meter. What should I ground my cable drop to? Should I run a 2nd cable down to the rod or should I ground to the panel?

  6. #6
    Join Date
    Feb 2012
    Location
    Kent, WA
    Posts
    216

    Default

    Current code requires an "Intersystem Bonding Termination" (250.94), although you don't have to meet current code. This is a multi screw bar that is mounted outside near the meter or panel and is used for phone, CATV, satellite, etc -- whoever needs a ground connection. There may be kits now at the home centers for this. One of the screws or lugs on that should take a larger wire (a #6 is required), and that can go to the ground rod, the main panel neutral/ground bar, or a few other places. If you have an exposed Service Conduit (threaded rigid metal), you may also find an intersystem bonding kit that will bolt to it. Just using a bare copper wire from the disconnect to the rod would give you a point where you could tap on grounds to other systems. But it will oxidize and corrode over time, so the block is a better install, or use an insulated wire which a person can strip if they want to tap on in the future. The code says you can use this for existing buildings without an Intersystem Bonding Termination (must be installed at the Service Equipment and mounted outside):

    (1) Exposed nonflexible metallic raceways
    (2) An exposed grounding electrode conductor
    (3) Approved means for the external connection of a copper or other corrosion-resistant bonding or grounding electrode conductor to the grounded raceway or equipment
    Mark
    Kent, WA

  7. #7
    Join Date
    Feb 2012
    Location
    Lala land, OH
    Posts
    235

    Default

    If I read this right this is something I can take care of after my ground rod is buried and done with. I don't need to run anything else to my ground rod...Correct?

  8. #8
    Join Date
    Feb 2012
    Location
    Kent, WA
    Posts
    216

    Default

    If you have a metal service conduit accessible on the outside of the house, or your main disconnect is mounted outside, then go ahead and bury the rod and GEC. Otherwise, you may just want to clamp on another #6 from the rod so you're covered.
    Mark
    Kent, WA

  9. #9
    Join Date
    Feb 2012
    Location
    Lala land, OH
    Posts
    235

    Default

    Thanks..

    Now to threadjack my own thread...
    The last thing I need to do before calling the inspector is my service riser. I am installing 200A service (meter/main) with a 100A feed to a sub panel that powers most of the house. My total demand load is about 115A with a 85A neutral load. I am trying to size my neutral for the riser and want to future-resistant it (not saying proof hehe). I am running 4/0Al up the riser (PVC-no mast) to the weatherhead for my hots. How much smaller should I make the neutral? 2/0 Al ok? There may be future (non continuous?) larger 120V loads down the road. (Air compressor, attic fan, etc) and I want to be safe for that.

  10. #10
    Join Date
    Feb 2012
    Location
    Kent, WA
    Posts
    216

    Default

    Since your calculated load is so low, it is difficult to answer. It only needs to be sized for the calculated load, and no smaller than table 250.66 (#2 AL). You can almost always reduce the neutral by 2 sizes without a problem. 4/0 AL is good for 180A, and 2/0 AL is good for 135A (assuming you can use it at 75C). If you can find an easy 45A of load that will never have a neutral, then 2/0 is easy to justify.

    You can work this backwards by subtracting your 240V only loads and applying a demand factor. For example, if you have 20A from a 240V water heater, and 25A from a 240V HVAC unit, that is 45A that will never have a neutral load. The optional calculation puts a 40% factor on most loads (although HVAC is 100%), so multiply 45A * .40 and you get 18A. So you can easily reduce the neutral by 18A (or take the HVAC at 100% so you'd get to reduce by 33A if still taking the water heater at 40%). If you have an electric range or clothes dryer, you can subtract off 12% of its nameplate amps for a neutral reduction too. Anything else purely 240V you have connected?

    You should have no problem running three 4/0 conductors up a 2" pipe if you don't want to reduce. You only need one size of wire that way and have a bit more leeway on cutting and waste when you only use one size.
    Mark
    Kent, WA

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