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New 30 Amp Shed Sub Panel underground electrical feed. - Should I use 10/3 UF-B or 10/2 UF-B and is

Post in 'DIY and General non-hearth advice' started by Don2222, Nov 26, 2011.

  1. oldspark

    oldspark Guest

    I may be wrong but I think you ground a sub panel every where. Not sure why you would want to take the chance of burning up the run of wires if there was a short to ground, the neutral will be grounded in a sub panel, never heard of not grounding one because you have a ground rod.

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  2. oldspark

    oldspark Guest

    I looked it up and they want the neutral to float (I hate floating neutrals) but the sub panel is supposed to have a ground rod, how you define sub panel can be an issue also.
  3. Hass

    Hass Minister of Fire

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    Yeah, that's why I suggested he just call up the inspector and ask what he wants. Considering it's 150' feet away he should most likely have one. But, if it's wired improperly I have a feeling the results would be worse than if he did not have a ground rod at all.
  4. Don2222

    Don2222 Minister of Fire

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    Thanks again BeGreen, you are the expert!! I did get the 10/3 UF-B. Originally I was at Home Depot in Methuen MA at their rental shop. So I checked and they had the 10/3 UF-B for $2.07 per foot and 6% sales tax! So I said keep it and went to Lowes in Salem NH. It was $1.94 per foot except their 1000 ft roll was so tangled they got 78 feet off and could not get anymore!! Luckily a real electrician customer came by and showed them how to untangle it by removing the roll from the rack! By then there were 4 Lowes employees there after explaining to the dept mgr Jeff what had happened! So I complained to Jeff that it has been 1 hour to get my wire and if he could do something! So he told me I could have it for $1.50 per foot!! Then the Lowes charge card takes another 5% off!!

    Did I get a good deal??
    Batman likes this.
  5. btuser

    btuser Minister of Fire

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    The distance from the main panel is the key, also depends on whether or not the building is attached. Installing a ground rod at a sub panel can do more harm than good in the right situation. Things like this are better left to the AHJ. He/she may have experience with your local, when the end result can depend on such subtle nuances as soil conditions and knowledge of city water projects. New main lines are plastic.

    My knowledge of grounding is biased towards telecommunications. Because we were always plugging into power and had our own system ground we were forced to bond to the main electrical ground with a minimum of 6 gauge solid copper. This was to avoid a grounding conflict. There should be only one path to ground, and if you've got two you need to bond them together but NEC says a minimum of 6 gauge solid copper . When I did my last shed I ran 10 gauge in conduit to a sub panel. 2 hots and a neutral and 2 ground rods at the sub panel. No ground back to the panel. My inspector said this was the way to go, otherwise you need to bond the two grounds with a minimum 6 gauge solid copper conductor. Was he agreeing with me because his mom was my neighbor and I cut her grass for free? Possible but there is probably no more confusing subject in the NEC than grounding.

    My pool was installed in 2007. The electrician installed a 30 amp sub and ran the ground 200' back to the house with no ground rod, no expansion joints at the house/pool, used mc outside to wire the pump, and a couple other things I'd get nit-picky about if I was the one who paid for it (house came with the pool). This work was inspected and passed.
  6. nate379

    nate379 Guest

    When I did my shed I just bought a roll, I want to say it worked out to around $1.25/ft. What I didn't use I sold. The stuff they cut is fine if you just need a few feet, but if you are close to a full roll length it's much cheaper to buy a roll instead.


    As far as how to wire it up, I'm done with posting on here... I could say snow is white and someone would argue it. I do agree that some locations have different codes, but please check out the NEC for what you need.


  7. oldspark

    oldspark Guest

    Nate I dont blame you and some times I feel the same way, the ground rod is a given if the sub panel is in another building and I believe every code SHOULD be the same no matter what the inspector says (they can be wrong and have been in many cases so you have to have the code book to show them). The "floating neutral" as they call it (every where not just here) is not a true floating neutral IMHO because it is grounded back at the main panel so I understand not grounding it again but the ground rod is called for on every site I looked and is in the NEC. There can be some instances where you may not have to use one if there are other lines (gas, comm.) between the two buildings. I just hope the OP does his own fact finding and not rely on answers here.
  8. Don2222

    Don2222 Minister of Fire

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    Wow, you are 100% correct on the grounds! The best way for everyone to understand this, is the harm that can happen when the ground is incorrect. I have that example. When we first moved into our home years ago we had an old harvest gold color Glenwood stove in the kitchen. My wife was cleaning one day and as she touch the stove control at the same time wiped the counter with a wet sponge and got a wicked electrical shock!

    Well I did many hours of research to see why this happened. I found that the way these old stoves were made is this:
    All the electrical components in the stove were grounded at different places to the steel shell. The steel shell was then connected to the neutral. A 3 wire cable with 2 hots and a neutral was then ran to the panel!!

    The front stove control that my wife touched on the control panel was grounded to the panel and the panel was connected electrically to the rest of the stove with 2 small screws on each end. Well the stove was 20 years old and the screws rusted!
    So my wife became the closest point electrically to ground and the current ran right thru her!!!

    So the 2 points you made should be very clear to everyone:
    1. Best to have only one ground for the current to flow!
    2. The ground should be close to the whole unit!

    I also found that the new stove I purchased now has 4 wires.
    One ground
    One Neutral
    Two Hots

    The new kitchen stoves now have all the electrical component grounds all connected together and should be wired to the Neutral wire.
    The stove shell is now separate from the electrical components and is connected to the Ground Wire.

    The ground and neutral and the 2 hots are run to the electric panel!!

    One ground and separate from the neutral!!

    So even though a ground rod could be used closer to the stove, it does not make such a difference that it is a safety hazard.

    The shed is very similar to the stove unless it is very far away.

    My shed is less than 50 feet from the house, but the circuit panel is on the other end of the house.

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  9. chrisf

    chrisf Member

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    Last time I knew all sub panels need a isolated ground. If not you can pick up the kit and install it in the sub. It is supposed to be sperate from the nuteral. They are less than 10 bucks for the ground kit. On 10 3 wire you have 3 condutors and a ground a ground wire is not counted as a conductor. So in 10/3 you have a black red white and a ground wire. In 10/2 you would have a black and white and ground wire. you should not have to have a earth ground at the sub since you have a ground wire feeding from the main to the sub panel .
  10. davmor

    davmor Member

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    The ground and neutral should only be bonded at a main panel, never at a subpanel.
  11. nate379

    nate379 Guest

    Yes they do need a ground, but your post is contradicting itself. You say it needs an isolated ground but your last line you say it doesn't. There needs to be a ground run from the main panel to the sub panel and also a ground from the sub panel to the ground. Ground rods, EUFER, whatever is approved in your location.



    I'm not an electrical engineer, all I know is if you look in the 2008 NEC it's under 250.32.

  12. davmor

    davmor Member

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    Some local inspectors do not require a ground at the sub panel, mine did. Glad I did it. Seems like overkill, but it is better to be safe.
  13. begreen

    begreen Mooderator Staff Member

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    Code changes. We redid our main and panel when adding the grid-tied solar. One of the changes was to completely float the neutral from the ground bus. It was in common before, but now the neutral bus is independent.
  14. oldspark

    oldspark Guest

    I have been an electrician for many years and I understand what they are doing, the neutral is grounded at the main panel and not again on the load side so it all makes sense to me. I assume your neutral is grounded some where because that is not good to have a true floating neutral and NOBODY does than or any code any where. Is that what you are saying that your neutral is not grounded any where even in the main panel?
  15. begreen

    begreen Mooderator Staff Member

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    We have two main panels now. Well, the house main panel is now technically a sub-panel. We gutted it, and floated the neutral in that panel. The main breaker panel is now outside and IIRC, the neutral is bonded there and only there. If it's dry out tomorrow I may pop the cover and take a confirming look.
  16. oldspark

    oldspark Guest

    Cool, I understand now and you have what you are supposed to I believe.
  17. Don2222

    Don2222 Minister of Fire

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  18. chrisf

    chrisf Member

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    What I am saying is you have a separte ground bar and nutureal bar in the sub panel. they both run to the same bar in the main panel. And would you run another ground cable and rod in a house if you put a sub panel in on the second floor? Its no different you are just running a longer distance from the main panel. I may not have explained myself in my posting your ground goes back to the main panel so what is the need for a second one at the sub right to ground.
  19. oldspark

    oldspark Guest

    "This is also sort of why a sub-panel in a detatched structure must also have a seperate ground rod. The electrical potential of the ground can vary from place to place. There can be a voltage difference between the ground under your house and the ground under your neibor's house. So when you add a sub-panel in a detatched structure, you want to make sure the voltage difference between ground wires (and appliace frames and pipes) and the ground AT THAT STRUCTURE are the same. To do so, you attatch a new ground rod to the ground bar of the sub-panel."
    Not sure if this is any help to you but the best explanation I could find.
  20. nate379

    nate379 Guest

    No because the sub panel would be in the same building. Only need to run separate ground if the subpanel is in a detached building.

    I don't know the exact reason why, I just know it's per the NEC and I wasn't going to argue it to save $25 (2 ground rods and some copper wire). I know it's been code for a long time, my Dad put in ground rod when he built the detached shop/garage in 1990. He had his cousin who is an electrician wire it.

    And yes you don't bond ground and neutral at the sub panel. Again I don't know the reason why, just that's the way it's done. I'm sure if I went to school for this I would understand it better. I'm just a jack of all trades so to speak and have wired up a few buildings.



    Anyhow, for the original poster, I haven't seen where you answered what exactly what going to be powered in this shed?

    You could save money if it's just 120v lights and a few outlets by not running a subpanel and running everything on 1 circuit. This is permissible by code.

    I did not do this in my shed because I ran 30 amp 240v since I have my air compressor in there. Since I put in a panel I put separate circuits for the lights, outlets and outside light and outlet. Though honestly it could have all gone on one.
    I have worked in some garages that the whole thing was fed off just a 15 amp breaker.
    Mine currently has 1 breaker for the door opener and lights and 1 other for the outlets, just 15 amp, 14 gauge wire. Rest of the house is almost all 12 gauge, not sure why they did that. There are a decent amount of outlets too, 2 on each wall.
  21. bluedogz

    bluedogz Minister of Fire

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    50A goes to the panel, there are 3 circuits in the panel running 1 outlet apiece, 1 more running 3 overhead fluoro fixtures, and one specifically for a window A/C if I ever get around to buying one.

    Oh, yeah- the barn is 28x28, not 28x278, in case anyone didn't catch that.
  22. oldspark

    oldspark Guest

  23. jharkin

    jharkin Minister of Fire

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    Don I believe you are confusing the role of neutral and ground.

    - Neutral is the return conductor for 120v current at zero volts.
    - The "ground" in a residential AC system is a safety feature. It NEVER carries current except when there is a fault.


    Before 1996 the NEC treated ranges and dryers as a special case where the neutral wire was allowed to do double duty as a ground. So the frame would be tied to the neutral in the 3 wire (hot/hot/neutral) plug.

    I'm actually surprised your wife got a shock even on the old rage. The only part of a stove that uses the neutral are the 120v controls and even on older units I believe this neutral connection was wired directly back to the terminal block with just a single ground jumper connecting neutral to the frame. I wonder if there was another short in that control panel? (not that it matters now)....
  24. Don2222

    Don2222 Minister of Fire

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    No, I am not confusing anything. What you said above is correct in the current design of all AC electrical appliances. However it was not always that way. The house I grew up in that was built in 1890 had only 2 prong AC outlets and both prongs were the same size. There was no separate ground. Ground in those days was the return for the 120 and the ground!! Now that we know better, what you said is correct!

    My wife got a shock because the return current from the front control could not return thru the rusty screw on the control panel and went thru her instead!!

    Anyways, I did get the 10/3-UF-B and the 27 foot trench I dug went from 24" near the shed to 36" next to the house because the ground slopes up toward the house! Well below the 18" code for this area. See pics. We got the wire pulled just before it got dark today! Tomorrow I can make the connections. :)

    See pics Below. Click to enlarge

    Attached Files:

  25. begreen

    begreen Mooderator Staff Member

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    Must be something is not showing in the picture. Is that really a 150ft run? Our greenhouse is a 75 ft run and much longer than what's showing.

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