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I need to replace the service cable from the weatherhead to the meter box at my mother-in-laws house. No conduit involved. From the meter to the breaker panel inside was replaced at some point and is still in good condition. I've searched and from what I have read 2/0 al SEU would be required. Is this correct?

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  • The fact that you're asking this question tells me that you are most certainly not qualified to replace a cable from the weatherhead to your meter box. I pray that if you are doing this then your service is disconnected at the pole. The only thing making that cable 100 amps is the main breaker in the electrical panel. Please don't die.
    – MonkeyZeus
    Commented May 13, 2021 at 15:28
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    Thanks for the constructive criticism there Monkey. I am not an electrician, so no I am not "qualified" as you state. I am however very aware of the severity of the consequences when dealing with electricity. I replaced all the equipment at my home when I upgraded from 100 to 200 amp service. I involved city inspectors and the poco as required in my county. And obviously I did not die. Thanks again for your concern. Now if someone else would be so kind as to add positively to this post it would be most appreciated.
    – roasthead
    Commented May 13, 2021 at 15:42
  • I mis read no conduit as conduit but it won’t be a problem so long as the conductors are “protected”.
    – Ed Beal
    Commented May 13, 2021 at 18:03

2 Answers 2

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Depends if it's your entire service...

Normally the answer is "#1 aluminum".

However, if the 100A is your entire service, a "discount" kicks in: 310.15(B)(7) says you only need wire large enough for 83% of your service ampacity (83A obviously) so that allows use of #2 aluminum wire.

And you are better off using aluminum because the service drop itself will be aluminum, so why create a dissimilar metal problem?

... and if you want a "Heavy-up" later.

Honestly I'm a bit surprised that any power company is offering 100A service these days. Usually, they want you to take 200A service. And you may want to take it later.

And you know what: the difference in wire size cost outlay will not be large. So it may make sense to spend the extra coin today so your wires are ready for 200A later.

For 200A service, you will need 4/0 aluminum (or 2/0 copper). That's assuming again that it's your whole service and 310.15(B)(7) applies.

If the 200A is less than your entire service and you can't use the 'discount' then full-boat ampacity requires 250 kcmil aluminum or 3/0 copper.

Just to be clear: you never do this hot

To do any work on the service entrance cabling (weatherhead to meter) the power company must remove their service drop wire.

One option that can reduce downtime is to install a new, parallel weatherhead and meter pan right next to the existing one. Have the new meter pan be a meter-main (required anyway in NEC 2020) which then allows you to de-energize everything downline with the flick of a switch. Then, the power company is making 1 visit, and you can quickly punch over the. However, some power companies will want to see that the new work has passed inspection. Once the service drop is moved to the new weatherhead, the old weatherhead is stone dead, and you can easily de-energize the meter-main obviously.

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    Yes our power company requires a pre and post inspection before they'll disconnect and reconnect. My intent was to upgrade mother-in-laws service to 200 amp like I did at my house, but she doesnt want anything inside the house changed (old and stubborn in her ways I suppose). It's just her living there so it doesnt need to be upgraded for any reason other than a selling point if/when she's no longer on this Earth. Thank you for the response Harper.
    – roasthead
    Commented May 13, 2021 at 17:44
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    @roasthead Well that's not too bad. Nothing inside the house needs to be changed if you install a meter-main. The "main" part can be changed to 100A, but better, you can choose a 200A "Meter+main+mini-panel" and feed the existing panel from a 100A breaker in the mini-panel. Commented May 13, 2021 at 19:36
  • That sounds like a great idea, but I've had a couple discussions with her and she is adamant that nothing gets messed with inside her house. I'll have to wait until she is either mentally checked out of the game or deceased before I can upgrade. But at the minimum I'll swap out the 100 amp meter box with a 200amp and run 4/0 al up to the weatherhead.
    – roasthead
    Commented May 13, 2021 at 19:50
  • And anyway, she's not wrong. Since the 100A panel already in the house is able to power all existing loads in it, there's no reason to change much in that panel, unless it's an FPE or Zinsco firestarter. Even a Challenger panel only needs breaker changes, that's easy. Future loads can go in a "meter-main-mini-panel" or a second panel. Commented May 13, 2021 at 20:00
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Aluminum wire to a meter is really regulated by the utility after the meter the NEC has jurisdiction. NEC 338.10.4 limits smaller sizes to 60deg table but this is both in conduit and outside. So the meters listed temp will need to be considered.. Any structure requiring a 100 amp service:

If 60 is the meters limit 1/0 cable is fine for 100 amp aluminum.

If the meter allows 75 deg #1 is fine for 100 amps

Now if this is the supply for A residence an 83 of the service rating is allowed:

the 60 deg table would allow #1 aluminum

The 75 deg table would allow #2 aluminum

In all cases you can use larger wire and 2/0 would be fine i normally do use #2 but have run into service equipment that was only rated for 60 deg.
I believe this to be a residential but just in case I read into it I gave all 4 possibilities.

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  • This is a residence. I'll inspect the meter box after the power company cuts off at the pole and removes the meter. It is a pretty old one so will most likely need to be changed. Thanks Ed.
    – roasthead
    Commented May 13, 2021 at 17:52

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