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Been looking at this long and hard and finally threw in the towel and admitted to myself that I need some qualified help. Here's my situation. I recently had a 200 amp Square D Homline panel with 100 amp square D Homeline subpanel installed to replace the old fuse box mess I used to have. The 200 amp side is configured to service all of my electric radiant heat loads, and the 100 amp side takes care of all my lights and outlets for the home. What I would like to do is run a 125 amp run to my garage so I can have enough power out there for welding/shop tools/lights. The only way to get line to the garage is a perforation through the basement wall that travels right next to the sub panel for my well. My thinking was that I could remove the 240 volt/30 amp supply line to that sub panel and replace that sub panel with a small, 4 space sub panel. (Homeline 125 Amp 4-Space 8-Circuit Outdoor Main Lug Load Center with Ground Bar) Then feed the well pump with a 30 amp breaker from that. That would use two slots. Then I would install a 125 amp breaker in the other two slots to feed a sub-sub panel in the garage to do my heaving lifting out there.

So, I'm really just using the small panel as a means to connect two runs between the main 200 panel and the garage panel, tapping into it just enough for the well along the way. One thing I can't seem to get straight is that it looks like I'm supposed to use #1 copper for the 125 amp run, but the specs on the Square D 125 amp breaker say it's only big enough for #2. The run is only 35 feet from the 200 amp main to the garage. Will #2 wire suffice? Also, I expect I would have to add a lug to the ground and neutral bars on the 200 amp main, as well as on the sub panel at the well.

I hope I have explained all this adequately. Does it sound like I am on track here? Or am I out in the weeds? Really just want to get that power to the garage but I think I'm seeing a way to get rid of that obsolete shutoff at the well while providing an easy way to break that cable run into two parts. The first part being from the 200 amp box to the well shutoff, and that could be done in cable. While the rest of it can be individual wires run though conduit after it goes through the wall. That spot on the wall where the well shut off is is the only place where I can get a line through to the garage.

I live in North West Ohio if that helps with identifying code requirements.

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    You want to use aluminum wire anyway unless you are truly into wasting money. And you make a junction to wire that fits the breaker, near the breaker. You might also be able to skip the second breaker by using a "pass through" arrangement, but I'll let the guys that do more of that sort of thing get those details to you. i.e. if the "well sub-panel" is fed from a 125A breaker in the main, and has a 30A breaker for the well, and the wire continues on to the shop (protected by the breaker in the main) rather than having an extra 125A breaker in the well sub.
    – Ecnerwal
    Commented Jun 11, 2021 at 23:34
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    I am aware of the savings on using aluminum, but then again, if the Square D 125 amp breaker is only capable of taking #2 copper. I don't see how the supersized aluminum is ever going to work.
    – Thomas Tipton
    Commented Jun 11, 2021 at 23:37
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    Are you quite sure you are reading that right? I happen to have a 100A Square D breaker sitting here and it's labeled for 2/0 wire - which is 3 sizes larger than 2. 2, 1, 0, 00 which is also written 2/0. But it's QO, not Homeline.
    – Ecnerwal
    Commented Jun 11, 2021 at 23:53
  • I very well may be misreading that spec and things make a lot more sense from the perspective that I am. Thank you for that. I looked again and it says maximum 2/0. So I could use 2/0 Aluminum or #1 Copper. Now to clarify if I can add lugs to the neutral and ground buses.
    – Thomas Tipton
    Commented Jun 12, 2021 at 0:07
  • Your mentality of "I only need 4 spaces, I'll get a 4-space panel" is why you are always out of breaker spaces and have so many subpanels. Stop doing that. In the future, you will want more breaker spaces. Buy them now, they're dirt cheap in quantity!
    – Harper - Reinstate Monica
    Commented Jun 12, 2021 at 0:26

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Looked the Homeline breaker up. It is also labeled for up to AWG 2/0 wire, which is not AWG 2 wire.

In increasing size:

  • AWG 2
  • AWG 1
  • AWG 0 or 1/0
  • AWG 00 or 2/0

The breaker terminals are rated for 75C, so good for 175A in copper or 135A in aluminum.

This is, of course, only answering one part of your question.

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