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I am building a house and need to run wire from the meter to the breaker panel. I've pulled my own permit and done this before, but it was a short distance (~50') and I just went and bought 4/0,4/0,4/0,2/0 SER and wired straight from the meter to the panel.

In my current home though the distance from the meter to the house is going to be ~250', and needs to be buried underground, so I plan to use individual wires. According to the NEC, I should add 20% to the AMP for each 100 feet, so I am estimating 50% more which makes it 300 AMPS. Using the 83% rule, that means I need a wire sized for 249 amps, or ideally 300 MCM aluminum.

My issue is that the breaker panels I am looking at have a max wire size of 250 kcmil. And I am not really sure what the maximum wire size at the meter is either.

Do I just run 4/0 from the meter to a junction box located near the meter, then run 300MCM from the junction box to another junction box near the front of the house, and then 4/0 from there to the breaker panel? Is there another obvious solution I am missing here?

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    It isn't exactly clear whether this meter and main panel are both mounted to a very long building, or whether there'll be an outdoor aerial or underground segment in the path. SER can't be used underground. Cable (or pre-twisted triplex/quadplex) will be a hassle to drag through that much conduit; use individual conductors instead. See another question there
    – Greg Hill
    Commented Oct 3, 2023 at 17:10
  • You are 100% correct, I was remembering incorrectly! In my previous home the meter and the panel are located on the house themselves within ~15' of each other. For that I used SER. For some reason I was mixing that up with the run from the utility company to the meter. I will absolutely use individual wires for this, but still my situation remains the same. The meter is on the corner of the property, and I need to run underground from that to the panel located on the house ~250' away.
    – esac
    Commented Oct 3, 2023 at 17:21
  • Are you under NEC 2020 or something earlier? Will you have a main breaker at the meter? If not, have you asked your local electrical inspector if they will really approve a 250' unprotected feeder?
    – nobody
    Commented Oct 4, 2023 at 2:11
  • Yes, we have adopted 2020 NEC. Honestly I do not know what is in the meter box they have, it is possible that they have a breaker in there, but yes they allow 300' from the meter to the panel.
    – esac
    Commented Oct 4, 2023 at 15:28

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According to the NEC, I should add 20% to the AMP for each 100 feet, so I am estimating 50% more which makes it 300 AMPS.

You're not getting that from the NEC. That is not in the book. NEC doesn't even have a rule about wire size increases for voltage drop.

250 kcmil will be fine. Generally 170’ is about where you need to think about maybe checking the voltage drop calculator, and 250 kcmil is 1 bump.

If you check the voltage drop calc, remember 3% is not critical and make sure you use 160A not 200A. If you actually plan to load to honest 200A, you would need a 250A service.

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  • Thanks, I see this all over for example here is just one thewiredshopper.com/200-amp-wire-size According to the NEC 310-16 rule, you should increase the amps for a 200 amp by 20% for every 100 feet. This will help account for the voltage drop.
    – esac
    Commented Oct 3, 2023 at 18:02
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    @esac that site is flat wrong. A great many "help sites" on the Internet are actually written by search engine marketers to show ads. They pay English speakers in desperately poor countries like Bangladesh a penny an article to hand write articles stuffed with all the right keywords (the word processor cues them on keyword density etc.) It's all about volume and they do not care if anything is accurate. I spend a lot of time in NEC 310 DOT 16 (not DASH 16). Go read it yourself.
    – Harper - Reinstate Monica
    Commented Oct 3, 2023 at 18:23
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    And FYI 310.16 is 310.15(B)(16) in the old numbering, that's easier to find. And you use the 75C column in that table.
    – Harper - Reinstate Monica
    Commented Oct 3, 2023 at 18:29

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