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400 AMP service – Feed Line Question

This topic contains 5 replies, has 3 voices, and was last updated by  Biggyniner 2 months, 4 weeks ago.

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  • #727375

    Hi,

    I’m installing my own meter base and panel for a 400 AMP service in my shop. Does anyone know what size feed line I should be using? I referenced table T. 310.16 of the NEC but I am still a bit confused as how to read it correctly. Any enlightenment would be appreciated.

    Here is a link to the table I am referencing:

    https://media.distributordatasolutions.com/ThomasAndBetts/v2/part2/files/File_7437_emAlbumalbumsOcal20(USA)oc_1_g_nec31016pdfClickHerea.pdf

    #727388

    CB
    Pro

    Hi,

    I’m installing my own meter base and panel for a 400 AMP service in my shop. Does anyone know what size feed line I should be using? I referenced table T. 310.16 of the NEC but I am still a bit confused as how to read it correctly. Any enlightenment would be appreciated.

    Here is a link to the table I am referencing:

    https://media.distributordatasolutions.com/ThomasAndBetts/v2/part2/files/File_7437_emAlbumalbumsOcal20(USA)oc_1_g_nec31016pdfClickHerea.pdf

    Firstly, recognize that the 310.16 conductor ampacity table you are referencing does not account for voltage drop over distance, only the thermal limit rating of carried current for the type and diameter of the conductor, which is dictated by the factors defined on the table.

    Those factors are:

    The temperature rating of the conductor. (top row)
    The insulation class of the conductor. (next row)
    The type of metal the conductor is made of. (next row)
    The diameter of the conductor. (first and last columns)

    The ampacity ratings occupy the rows and columns in the center of the table, as indexed by the peripheral rows and columns.

    You haven’t identified overhead or underground service, single phase or three phase, pole to meter pan or meter to main panel, whether you are splitting the 400 service into two 200 amp subpanels, whether your service supplier requires a Current Transformer meter base, since you are installing larger than 320 amp service…

    Are you sure it wouldn’t be worth your while to hire an electrician to do what you are doing? For liability and compliance reasons, it might be worthwhile calling in someone who knows what your power company and jurisdiction require, nevermind knowing how to read tables found online.

    #727392

    Seven-Delta-FortyOne
    Pro
    The Emerald Triangle, Northern California

    I’ll start out with the bad news: Service Entrance calcs are not for the inexperienced.

    There is the whole subject of the load calcs, which must be done to determine what size service to install. But I’ll skip that for now.

    If some of the load is continuous duty, you’ll have to size at 125%.

    The table you’re looking at is outdated. It’s now 310.15(B)

    I don’t know, as CB mentioned, if it’s single-phase, 3 phase, OH, UG, in conduit, direct burial, or what.

    Also don’t know about distance, which will need voltage drop calculations.

    And I don’t know what type of panel you are getting. If it’s rated for 90C, you can use a smaller cable.

    But VERY preliminarily, it looks like somewhere between 500KcMil and 750. That’s enormous cable.

    There is also the possibility that you could do parallel runs, but they have to be done perfectly, or you’ll blow the whole system.

    And your panel has to be sized for the maximum available fault current from the transformer secondary. POCO will have that info.

    I highly recommend you either hire an electrician, or at least have one draw the plans and submit them. Then at least you’ll have some more eyes on the project.

    Goin' Down In Flames........

    #727592

    Overhead service, from the weather head to the meter base. (Pole/Transformer, to weather head is power companies responsibility). I worked with the power company to determine at max the shop would have an 8KW load. The purpose for the 400 AMP service is for 2 200 AMP services, 1 immediately (for the shop) and 1 later on (Mother’s ADU).

    Thinking this panel:

    https://www.amazon.com/Square-Schneider-Electric-42-Space-42-Circuit/dp/B00KHVMA6E?ref_=fsclp_pl_dp_3

    This meter base:

    https://www.homedepot.com/p/Milbank-400-Amp-4-Terminal-Ring-Type-Link-Bypass-Overhead-Meter-Socket-R3548-X/202504185

    Also thinking 4 inch conduit is a must for the size of wire.

    #727593

    Seven-Delta-FortyOne
    Pro
    The Emerald Triangle, Northern California

    Do you have a copy of the NEC?

    If not, you need to get your mitts on one right away.

    We can’t just guess, or “I’m thinking this size”, when in comes to conductor sizing, wiring methods, or conduit sizing.

    It’s all laid out VERY specifically in the Code.

    Annex C will have all your conduit fill tables.

    You can go larger, especially if you have a long run you should. It’ll make pulling wire a lot easier.

    But first, you need to nail down your conductor sizing.

    And remember, you can’t have more than 360 degrees of bend without installing a pull box.

    Goin' Down In Flames........

    #727666

    Thanks for the reference to the NEC annex C tables.

    I made an assumption since the Milbank meter base has a max of 4in conduit and a max size of 600 Kcmil wire at the lugs, that I should be able to fit 3 600 kcmil wires in the 4in conduit and be ok. Smaller size wire would obviously be fine.

    Luckly I have no bends planned, it is a straight run from the weather head to the meter base.

    This does leave a question however with regard to the line from the base to the panel. Since I am only running a 200 AMP panel for now in the shop, can I feed that panel with standard 200 AMP service line? When I do add the second 200 amp panel for my Mother’s apartment down the road, can I pull another 200 amp service line off those lugs, or do I / Should I have a distribution box installed with 2 200 AMP breakers and feed the panels from there?

    I appreciate the tips and advice, as I am trying to learn this and save some money. Most electricians are reluctant to answer my questions as they want to make money – which I completely understand.

    Thanks

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