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In Can I use a main breaker as an “occasional” disconnect switch? I asked whether I can put (back) my 200A breaker and use it as "occasional local disconnect" in my 200A sub panel that is fed by a 100A feeder and protected via a 100A breaker in the main service panel. Surprisingly and to my big content, the answer was yes. (The only concern that was brought up was the "switching action" because the breaker is not designed as a switch and can't be used as such on regular occasion).

Now, very excited, I was about to put it in. But I want to ask again from a different angle: I mentioned that the feeder is 100A and it's size is 2AWG. But the breaker is still a 200A breaker. Can I put the AWG2 in its screw terminals? (Note: I previously though it was 4AWG)

This is how the breaker in question looks like:

enter image description here

On the label, it says "75C Wire Only, Torque 250 lb-in. Wire Range - 1-300kcmil CU-AL"

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  • Actually, I just realized 1kcmil would correspond to AWG #20. This screw terminal supports such a wimpy wire? Hard to believe. Do I really read the label correctly? I wanted to delete this question but given the importance of safety, I would like to keep it and hope someone can double confirm.
    – divB
    Commented Dec 9, 2023 at 9:33

3 Answers 3

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That actually is #1 AWG thru 300 kcmil. The #4 is technically too small for a listed termination. To make a compliant termination will require use of pin reducers, or insulated lugs which can splice your #4 to a piece of #1 (or bigger) which is allowed in breaker.

Response to comment;

Welllll, there's a lot things you CAN do, many of which I'm sure would never give you a problem. Just because something is, or should be, bullet proof, does not make it code compliant. For a compliant install go to home Depot, grab 2 of these, home Depot lug And 1 foot of #1 thhn wire.

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  • His problem is the wrong way round for pin reducers, but splicing 1AWG pigtails onto the #4 using some Polaris connectors or the likes would work Commented Dec 9, 2023 at 15:41
  • @ThreePhaseEel oh wow good that I asked again. Is there any easier solution? For example, can I use the metal clamps that they put in instead ? snipboard.io/IJgpuM.jpg (screw the metal clamps into the breaker instead of the bus bars)
    – divB
    Commented Dec 10, 2023 at 0:40
  • Thanks a lot! I ordered these clamps and purchased one foot of #1. I also checked and the existing feeders are actually AWG 2 (I will update my question). I assume this does not change anything, right? Still too small for the 200A breaker?
    – divB
    Commented Dec 10, 2023 at 22:48
  • That is correct. Good luck
    – Keith
    Commented Dec 11, 2023 at 7:46
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I mentioned that the feeder is 100A, so it is AWG4 copper (I believe).

4 AWG copper is not legal for 100A. If you think it is, you're reading the wrong table. That happens a lot.

You need 1 AWG aluminum for 100A, and the 200A main breaker will fit that.

If replacing the #4 copper feeder is not going to work for you, then change the supply breaker to 90A (85A wire + 240.4(B) Round Up Rule) ... and then install a 100A main breaker for that panel. The 100A will definitely take #4.

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  • I checked again and it seems the existing feeder is 2AWG. So should be good.
    – divB
    Commented Dec 10, 2023 at 22:46
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    @divB perfect... 2 AWG copper is good to 115A by the way. Commented Dec 11, 2023 at 7:06
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Harper's answer is correct about 4 AWG wire. But here is what I think happened to get you into what is currently an illegal situation:

  • Original service 100A.
  • Service feed gets a favorable 83% derate, so 100A service only needs 83A wire.
  • 4 AWG copper wire is OK for 85A. This was an old installation and used copper even though the usual wire for feeders has been aluminum for decades.
  • No internal feed (e.g., between main panel and subpanel) ever requires larger than the service feed, so a 100A subpanel off of a 100A main panel with 100A service is also OK with 85A wire.

So 4 AWG copper was OK originally. Then you got a 200A main panel and service upgrade. At that point, technically your 4 AWG copper was no longer valid. Your options should have been:

  • Replace the feed breaker with a 90A breaker. That is legitimate because there are no 85A breakers so you can use the next size up.
  • Replace the feed wires with 3 AWG copper or 1 AWG aluminum.

If you decide to replace the feed wires then you should look at the big picture first and consider whether larger wire for future expansion makes sense. But at least we know the reason the electrician took out the 200A breaker in the first place: It wouldn't work with the existing feed wires.

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    Thank you, that's great input. I checked and it's not ewasy to identify the wire gauge but I think I found a faint" 2 AWG" on one wire and a "#2" splice. So it seems to be AWG2. Still too small to directly connect to the breaker but good for the 100A.
    – divB
    Commented Dec 10, 2023 at 22:46

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