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I have an existing 100/125 amp meter panel with 4 used spaces (2 100amp double breakers = 4 spaces used). The power comes in from underground through metal conduit into the bottom of the panel. Power goes out the back to 2 basement sub panels. I am looking to replace this panel with a new 125 amp meter panel with 4/6 spaces. I am wanting to run a third sub box with power going out the bottom through 1-1/2, or larger, to a shed 100 amp sub box max 90 feet away. I am looking to use SER 2/0, 2/0, 2/0, 1 AL cable. Both ends of the PVC conduit will be secured to the meter and sub boxes. Also are the 2/0's for Hot, Neutral and Common and the 1 is the ground? Where will I attach the ground?

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    1 - Generally if you use cable then you don't use conduit. Conduit works best with individual wires. 2 - With 3 subpanels, I would seriously consider making this main panel larger - e.g., 200A. 200A is the general standard size, and even if you don't have 200A service right now, it would allow you to upgrade in the future if/when your utility can provide it. If you put in a 100/125A now then you will have to do another replacement later - better to spend a few $ now and be all set. Aug 2, 2023 at 3:25
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    Any chance you can post a photo? Is there a main breaker or just the multiple 100A breakers? Aug 2, 2023 at 6:55

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Since your description mentions that you have conduits connecting the boxes, you should not use cables at all. They have terrible conduit fill (because they have to be treated as a round of the largest dimension for oval/flat cables) and they are quite difficult to pull as compared to individual wires.

It's concerning that you are proposing DIY service entrance wiring and yet "Common" is one of the wires you think you have. In USA/Canada spit phase, you have Hot, Hot, Neutral and Ground. There's 120 volts from hot to neutral (in both cases) and 240V (or sometimes 208V if from a 3-phase transformer) between the two hots. The Ground conductor can be smaller than the hots and neutral.

The ground conductor attaches to the grounding bar in the sub-panel, and to either a grounding bar or to the neutral bar in the main panel, but in your case the bond (and main panel) is probably at the meter-main, so all other panels are sub-panels and should have grounds on grounding bars only, and neutrals isolated from ground, as neutral and ground are only to be bonded one place, at the service entrance. The shed will also require grounding electrodes - if it's not built yet, put a concrete encased electrode in the foundation (they cost almost nothing if planned for, and are the best grounding electrode you can get.) Otherwise a pair of rods at least (but more is better) 6 feet apart is the minimum.

For 90 feet at an honest 100A, 1 AWG aluminum is quite sufficient, and 2/0 is massive overkill. By which I mean a waste of perfectly good money on a wire size that's not going to save you anything, unless you have unstated plans to run a lot more current out there. For considerably less money than that, if you can manage with a 90A feed breaker to your 100A sub-panel, (or 150, 200A - the sub-panel only needs to be equal to or greater than the feed breaker, they don't have to match) 2AWG aluminum is sufficient, and tends to live in a price sweet spot.

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  • 1. Talked with former electrician, convinced me to go with 200 amp service/meter panel. 2. Conduit not run yet, shed not built yet. What size single wires should I run from the service panel to the 100 amp shed breaker box? 4. How many wires (Black-Hot, White-Neutral, Green-Ground)? 5. Does it matter Copper or Galvanized electrode? 6. How much should be sticking out. 7. Does it need to be completely in concrete ort some sticking in the ground? (Foundation post will be 4' deep) 8. I am presuming that the ground wire will also get attached to the electrode.
    – Rick
    Aug 2, 2023 at 23:20
  • @manassehkatz As above I talked with a former electrician and he, like you, suggested to go with a 200 amp panel. Thank you.
    – Rick
    Aug 2, 2023 at 23:24
  • @harper - Reinstate Monica The pictures I have are too big, in size, to send. If you know of a way to make them (3 pics) fit that would be great. Thank you
    – Rick
    Aug 2, 2023 at 23:27
  • @harper - Reinstate Monica There are 2 each 100 amp double breakers in the Service panel.
    – Rick
    Aug 2, 2023 at 23:30
  • @Rick Please take the tour. If you have 8 more questions and can't find the answers to them by searching, ask each question as a separate question, not 8 questions in a comment (nor 8 questions in a question.) If the questions are enlightened by the related questions, provide links between the related questions. You need 4 wires between the panel feeding the shed and the shed. Two hots, one neutral, and one ground. At these wire sizes (4 AWG and bigger) they may all be black, but the neutral and ground will have to be marked white and green, or the ground may be an uninsulated wire.
    – Ecnerwal
    Aug 2, 2023 at 23:51

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