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Thread: Wiring a Metal Storage Building

  1. #1

    Default Wiring a Metal Storage Building

    I am having a 24 X 30 metal storage building constructed behind my home. I plan to have a separate electrical service with a meter ran to it. I am going to do all the wiring to it as I did to my home 2 years ago.

    Because it is a metal building and a storage shed, I know the material and requirements are different. I have several questions.

    1) The meter pan & service wire will be a 200 amp. Can I put a 100 or 125 amp main disconnect?
    2) I assume because it is a metal building, I need to use some type of metal cover for the wires going to the receptacles and lights. Does it have to be EMT or can I use MC cable.
    3) Are there minimum requirement for lights & receptacles, like in my home receptacles every 6’ in living areas?
    4) I have a copy of the 1999 NEC book. Are there specific articles that may help to answer my questions?

    Any help would be greatly appreciated……….

  2. #2
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    First question - why a separate metered service for this building? That will most likely cost you $5 to $15 per month even if you use no electricity. The electricity used will be in addition to this minimum meter fee. Can't you run a feeder from the house to this building, or is it way too far?

    If you're installing 200A service entrance conductors, why install only a 100A main? Yes you can do this, but the big wires may not fit. I'd put in a panel that is sized per the service entrance conductors.

    I don't think the fact that the building is metal affects much other than you probably have no hollow cavity to run wires in. In this case, you'll have exposed wiring which is probably considered "succeptable to physical damage". You'll have to use a wiring method that can tolerate damage. Romex, AC, and MC cable can not. You could use EMT, sch 80 PVC, or IMC/Rigid metal conduit or wireways/wiremold.

    The metal frame/skin of the building is probably going to have to be bonded.

    Minimum lighting or receptacles depends on the use of the building. If its not a dwelling (see the NEC definitions page), then you don't need the 6/12 receptacle spacing rule, a 3 VA per square foot rule, or a minimum lighting level. If this is going to be a business, then the commercial rules would apply. An accessory building on residential property has few minimum rules.

    The 1999 NEC has many sections that apply to what you're doing. Services/ outside feeders (225, 230), grounding (250), wiring methods (all of chapter 3), All of chapter 1, probably a bunch of other stuff.
    Mark
    Kent, WA

  3. #3

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    There are 2 reasons for a separate service, 1) the distance is rather far from the house breaker panel & 2) I would have to bore under my driveway. I work for the utility company that services my area. The installation will be extremely cheap and the monthly service charge is only $7.50. I plan to connect my pool pump to this meter, so I will have usage each month.

    The reason I would run a 200 amp service is for future needs. Although I do not see ever needing that big, I only want to do this once. However, I really don’t think I will ever need over a 100 amp main disconnect. While the running of the electrical service to the shed will be cheap, I still have to purchase the rest of the material.

    This is only going to be a metal storage building to store garden and power tools. It is not attached to my home nor will it be used as a building. I would like to start with four 4’ florescent lights on 1 circuit and maybe a ˝ dozen receptacles on 2 different circuits. It is my understanding, the receptacles need to be GFCI .

  4. #4

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    I have a metal frame building. It's has a sheetmetal as siding.Theroof is in sheet metal. How do I ground or bond the framing of the building. What kind of clamp do I attach to the siding. What size wire? The service will be a 100amp or 200amp maybe?

  5. #5

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    Here's a picture of my Garage made of metal:
    Attached Images Attached Images  

  6. #6
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    The inspector made me bond my metal pool shed and he also wanted a light above the panelboard in that building. So I did both requirements with a single circuit. I ran 10-2 from a 15A breaker to a metal light fixture box that was bolted to the ceiling. I scraped paint from under the box strap where I bolted it to the roof peak support. Terminating the #10 ground in the light circuit to the box also bonded the building. I installed a cheap porcelain keyless lamp holder.

    I was worried that he'd want this bonding wire sized to 250.66 instead of 250.122. This would have required a #8 instead of the #10 I ran. If you can securely bolt your panel to the building structural metal, then that could bond it. My panel was on wood supports in the middle of the building.

    I'm not sure if the receptacles inside the shed require a GFCI. If this building is a garage they need it. If it has a bare or concrete floor, I would GFCI them regardless if the code requires it or not.
    Last edited by suemarkp; March 6th, 2006 at 09:13 PM.
    Mark
    Kent, WA

  7. #7
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    If you can securely bolt your panel to the building structural metal, then that could bond it.
    This could work, but you will want to run an extra bond from the panel to the metal siding (as an extra precaution)--using a clamp or such as your fastening for the bonding jumper. Make sure the wire is close to the panel. You could also run a clamp from your siding to the supplimential grounding conductor being ran to your ground rods. The wire coming the panel to the rods must not be broken (cut) to accomplish this. Wait for others to comment.
    Last edited by Ohm1; March 6th, 2006 at 11:50 PM.
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  8. #8
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    I believe the code covering this that would be applicable is 250.104(c). Which would require the siding to be bonded if the building is supported by structural steel. If it is wood framing covered by metal the siding is not required to be bonded.
    I agree with Ohm .... it is a good idea to bond the metal siding to the grounding electrode system or to the service enclosure as mark suggests regardless.

  9. #9
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    Attach the bonding lug (See lug below. Note: Lugs come in different sizes) to the side of your Garage with a nut and bolt. Run a piece of bare copper--use the same size bare copper wire you used for your ground rods--from the panel to the bonding lug. This should qualify the bonding requirement for your siding.
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  10. #10
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    PS: You only need a short run of wire.
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