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Wiring new shed, ground rod?

Post in 'DIY and General non-hearth advice' started by thinkxingu, Apr 5, 2010.

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  1. thinkxingu

    thinkxingu Minister of Fire

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    Hi All,
    Next Saturday, I'll be wiring up my new shed (built August of last year) and there are two electricians involved: a good friend and my brother-in-law! One says I should use a ground rod out in the shed, the other says I shouldn't.

    I'll be running 8AWG wire to a 6-breaker panel (100' run) just in case I want to ever add 220 out there.

    What do you think?!

    S

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  2. seige101

    seige101 Minister of Fire

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    Yes, since it will be considered an outbuilding with a seperately derived system. (at least i think thats what i wanna call it, no coffee yet though) You will need to run 4 wires to the subpanel, 2 hots a neutral and a ground. What size 220 loads would you ever be using out there? I would upsize the wire to #6 to reduce any voltage drop.
  3. PapaDave

    PapaDave Minister of Fire

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    Might have been overkill, but I ran #2 out to my pole barn about a 70' run.
    Oh, and a sparky my brother knows said to use 2 rods at least 6' apart, 8 ' deep. Did that too.
  4. woodsmaster

    woodsmaster Minister of Fire

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    I'm not an electrician but I was told (not by an electrician) that if your running a wire with a ground from a panel box it will be grounded at the panel box. If the wire you run don't have a ground you obviously have to use a
    seperate ground rod at the building.
  5. vvvv

    vvvv New Member

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  6. oldspark

    oldspark Guest

    Why would you not ground it, all saftey codes call for grounding and been this way a long time.
  7. woodsmaster

    woodsmaster Minister of Fire

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    Wouldn't it be grounded threw the ground wire that runs to the panelbox in the house and altimitly the house ground rod ? Don't know the codes not an electrician but my shed has elec. with no ground rod. Should it be changed.
  8. lobsta1

    lobsta1 Member

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    I believe this is correct. Also, I believe that you have to remove the jumper strap in the subpanel that is between the grd bus & the neutral bus.
    Al
  9. billb3

    billb3 Minister of Fire

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    You're gonna need a ground rod for the TV antenna anyway.
  10. fbelec

    fbelec Minister of Fire

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    LOL got that right
  11. fbelec

    fbelec Minister of Fire

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    here in mass ( might be a national code) since it is a separate building you need a ground rod 8 feet long. only one. and the wire you run from your house panel needs to be 2 hots a neutral and a ground and then at the sub panel in the shed separate the ground bar from the neutral bar via the ground strap or the green screw on the neutral bar that goes thru the neutral bar and is screwed into the back of the panel. (depends on the brand panel you have) if you are using a #8 copper you can only use a 50 amp breaker or aluminum use a 40 amp breaker. i just did a sub panel in a garage i used # 4 aluminum and a 60 amp breaker for a 110 foot run inside 1 inch pvc pipe. don't forget to install expansion fittings on the pipe above the ground. one ground rod. the inspector said it was a nice job.
  12. benjamin

    benjamin Minister of Fire

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    Two schools of thought here,

    1. the more ground rods the better

    2. the shed is a subpanel off of the house service, the house service has the neutral bonded to the ground, but any subpanel has to have the neutral isolated from the ground. One ground bar that is bonded to the box and one neutral bar that is insulated from the grounded box.

    I think there are instances where it's not desireable to have multiple paths. I don't recomend this, just trying to explain the logic.

    Obviously if you're running three wires, two hot and one neutral, you ground your neutral. If you run a seperate ground and neutral, I'd still add one or two ground rods, but keep the neutral ungrounded.

    Not an electrician, but my work has always passed. I try to avoid quoting the code since the time I tried to explain something electrical to an uncle whose wiring I had just fixed and he pulled out his copy of the code (hard cover full edition) and showed me his name on the list of authors.
  13. dancarbo

    dancarbo New Member

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    The National Electrical Code Section 250-32 (B) Exception: permits the supply to an existing (not new) second building to consist of two ungrounded hot wires and one grounded neutral conductor, with the neutral conductor grounded and bonded to the service enclosure at the second building and tied to a grounding electrode. This does not apply if there is any other metal connection between the two buildings. (example; metal water pipe)

    Any other situation that does not fit the exception would require a forth grounding wire from building to building bonded to both service boxes.

    Since your building existed prior to the wiring I feel that you should come under the exception. But if you have to have it inspected, You should run this past the inspector.

    Hope this will help.

    Dan
  14. hkillam

    hkillam New Member

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    I agree with "permits the supply to an existing (not new) second building to consist of two ungrounded hot wires and one grounded neutral" and believe this is the proper and current NEC method. As for grounding rods, don't stop at the minimum requirement; drive at least two rods, and consider their location. Moist soil (under a downspout, or at low ground where water will puddle during hard rain) is best, gravel or other agregate is bad. Cant tell you how many houses I've seen with a single rod, driven in the most convenient place by the rushed electrician, that were in mostly backfill of gravel, right next to the foundation. And passed inspection. You only have to put in a grounding system once if you do it right.

    I think that the best source of understandable material on this subject (and I've read many) is "Wiring a House (Best of Fine Homebuilding)" by Rex Caldwell. Very good information, understandable, and goes into detail about where "Code Minimum" isn't enough.
  15. dancarbo

    dancarbo New Member

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    I agree with Hugh K. that one grounding rod may not be enough as the NEC is a minimum standard. The NEC says that if the ground rod does not have a resistance of 25 ohms or less to earth then a second ground rod is required. The second rod should be driven a minimum of six feet away. Since we have no practical method of measuring the resistance to ground (an ohmmeter will not work) additional ground rod or rods would be a good practice.

    Dan
  16. oldspark

    oldspark Guest

    If done correctly there is no reason in the world to have two ground rods on one building that I can think of.
  17. oldspark

    oldspark Guest

    The reason for the ground rod at the building is if there is a short to ground you do not tear up any more wire and equipment than necessary so each building shoud have it's own ground.
  18. Deere10

    Deere10 New Member

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    GROUND it Well worth the effort. I put up a shed last year and only have a couple circuits in it but still drove the 8ft grd rod in.Especially if lookin at 220 in the future. Do it now and do it right..
  19. Later

    Later New Member

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    We lost the neutral on our underground service a couple of years ago. The electrician who traced the break and repaired it also put in a "ground plane" consisting of multiple rods a spaced a couple of feet apart. He had said at the time that if we had the ground plane when the neutral broke, our equipment damage would have been quite a bit less, as a matter of fact we might not have noticed the problem right away. Don't think that he was blowing smoke, he only charged $50.00 for the rods, wire, and installation.
  20. oldspark

    oldspark Guest

    Why would losing a neutral cause damage to equipment, not sure I understand that.
  21. Later

    Later New Member

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    The way that it was explained to me is that the lost neutral caused the ground to float. The symptoms that we experienced were that the 240V service wasn't split evenly into two 120V legs, but some circuits saw 180V when others were at 60 volts, even this wasn't constant just varied all over the place until I opened the main breaker.
  22. oldspark

    oldspark Guest

    Interesting, not sure why a lost neutral would cause the ground to "float" as it still should have been connected and functioning. How much stuff did it ruin?
  23. Later

    Later New Member

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    Microwave, small cheap TV, light bulbs and I think it shortened the life of the refrigerator - died a few months later. With our sandy soil the single rod that we has may not have worked well as a ground.
  24. Highbeam

    Highbeam Minister of Fire

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    Those are all 110 loads so what happened is that your AC circuit was broken intermittently since it had a good hot wire. The push pull of AC wasn't able to push and pull too well so the voltage potential varied up to 110. Shouldn't have seen any higher voltage than 110 on those circtuits. Now your 220 circuits don't even use the neutral so they should have been fine.

    I have always been told that a subpanel at an outbuilding gets its own grounding system including ground rods. It will look just like a service entrance from the street where you only need three wires from the house. Hot, hot, and neutral. The ground will go to the rods.
  25. fbelec

    fbelec Minister of Fire

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    if you lose your neutral your ground better be good, or you'll lose anything that is not 240 volt. i had a case in my town here last year. the guy lost his ground and his neutral he lost 3 tv's, 3 cable boxes, his computer in his furnace, multiple light bulbs, 2 fluorescent ballasts, a computer, and a freezer. you got to see a 2 bulb fluorescent 4 foot fixture with 185 volts going to it. as bright as a 8 bulb fixture. back to grounding. check with the inspector of your town. we got a guy up here that doesn't care if you have a water pipe ground, if you do a panel change or service change he wants to see two ground rods hooked up. even tho codes say when you have a water pipe ground the addition of a supplemental ground rod has to be installed (that's one. he wants two.) if you question him on the code he asks for a ohm reading on that one rod, knowing that the only meter that can test that is what we call in the trade as a mega meter. they cost at minimum $1000.00 i don't know anyone around here that has one. in my opinion put one in, the rod costs $15.00 and some #6 copper wire. most guys will want to see a rod because if your running all aluminum conductors because copper is ridiculous as far as price goes, they want a good path to ground, the aluminum will blow apart quickly, the copper won't. there have been times when a out building has a bad ground or no ground and starts getting fault currents that would normally blow the breaker but didn't and were felt a mile away at some other barn where the cows stopped making milk and refusing to either go inside or outside. i have a electrician friend that was doing a panel change and got wacked off the neutral when installing it into the grounded panel. he got hit off the utility neutral because his was the only good ground on the street. long short, install a ground rod.
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