I'm adding a 40A breaker to my panel and I'm confused with the corner tabs. I can buy left or right tab breakers that use only one bus bar. I'm guessing the two pole 40A breaker has two tabs, one in each corner/side to catch both bus bars, but I can't see both sides of the breaker in the picture (see link for the breaker below pls). It also looks like I need to move a 15A breaker from the right side to the left to make space but that would make the number of breakers uneven so I would need a plastic cover like the one installed on the right. I'm including pictures of the panel with and without cover, as well as, close up of top and bottom breakers sections. BTW the panel is Challenger and the wiring for the 40A breaker will be going to the bottom of the panel.


Link to breaker: https://www.connecticut-electric.com/40-amp-two-pole-ubitba240

panel with cover panel no cover zoom in top zoom in bottom

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    Where is the main breaker? What is it breakered for? Any insight as to the size of the main feed wires? Aug 27, 2018 at 23:36
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    @Harper -- he has a 60A tenant main with #4 Al (apparently) feeder wires feeding this panel Aug 27, 2018 at 23:40

2 Answers 2


Stop faffing with the Challenger breakers, pull out the bottom right 15A breaker, and install a BR115 bottom left and a BR240 bottom right

Buying "new old stock" or newly made Challenger-style (UBI/Connecticut) breakers is an expensive and frustrating exercise, so why are you insisting on trying to go through it? Eaton BR breakers are cross-listed and cross-labeled as type C (or type A for BD/BQ tandem/quadplex breakers) and can be safely and legally used in Challenger panels, as per this letter from UL to C-H (and see my answer here for more details); never mind that a BR240 is $10 and available anywhere in the USA, while the 40A UBI Challenger-style breaker is $50, harder to find, and probably not as good as the Eaton breaker (UBI seems to have...issues with breaker QC and QA).

If you really insist that the bottom left slot stay free, you can get a single, quadplex, BQ2402115 breaker and use it to replace the 15A breaker bottom-right as well as provide the new 40A circuit and a 15A spare. This is costlier than using the two full-size breakers, but still more reliable than the UBI breaker, and no costlier than the UBI part for that matter.

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    Nice score, ThreePhaseEel! I had no idea common Home Depot BR breakers were UL listed to play in Challenger and Westinghouse panels. Aug 28, 2018 at 0:08
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    @Harper -- the Westinghouse part is fairly easy because Bryant Electric was a subsidiary of Westinghouse for all those years -- the Challenger one happened when Eaton/C-H snapped up the remains of Challenger after they ate Zinsco and proceeded to choke on it... Aug 28, 2018 at 0:09
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    Oh, that's funny. We like to use Westinghouse and GE wherever possible for historical reasons, in honor of their monumental battles in the electrical industry. I'll make a note that BR ~= Westinghouse. Aug 28, 2018 at 0:31
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    You're thinking of a half-width two pole a-la a THQP2xx @JimStewart. Sep 11, 2018 at 19:42
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    @JimStewart -- THQP-style half-widths, yes, but those aren't really a thing for Challenger panels any longer -- using the full-width BR breakers is a far better bet. Sep 11, 2018 at 19:53

Pigtail off the 40A breaker you already have.

Why? Because this panel is seriously oversubscribed already. Put the A/C and the electric car charger on the same 40A breaker, and don't run them at the same time ever.

This way at least they'll trip the shared 40A right here instead of making you put on pants and shoes and trudge off to wherever your main breaker is. In the dark.

Occasionally, folks ask about automated ways to sense current and disable loads when other loads are high. You could use something like that. Since all your wires go upwards, it wouldn't be hard to group all the branch circuit L1 hots into a bundle, and the L2s likewise.

If I had a Siemens, ya ha...

If you get that big panel, get a Siemens. There's a $20 strap kit that lets you interlock two 2-pole breakers so only one can be on at once. Then you can just make A/C and EV charger mutually exclusive. (the kit is made for generator interlocks, but it'll work fine forward-feeding too.) Of course that gadget takes 4 spaces, so it's a privilege of having a big panel.

Get a handle-tie for breakers 2 and 3 also

I did a quick look. Disregarding the A/C, which doesn't use a neutral, I see 9 hots and only 7 neutrals tapped. Two of your circuits are *multi-wire branch circuits. (MWBC) These need to have their handles tied.

The first pair is #2 and #3, and the other pair is #4 and #5.

If you look at the weird bit of metal on breaker 4, that's what that is. Get another one for breaker 2.

The good news is the MWBCs are correctly positioned so they don't overload the neutral. When you convert to that big panel you want, make sure to land those pairs of wires (2-3 being one pair, 4-5 the other) on 2-pole breakers. This is absolutely essential or you will overload the neutral.

  • Funny. There was another one of those metal pieces sitting at the bottom of the box. I thought it was a spare. I guess they forgot to place it. Thanks.
    – Rodo
    Aug 28, 2018 at 5:25

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