I want to install a 48A EV charger. This would require a 60 amp dual pole breaker.

I want to run this to my sub panel, which is a Challenger catalog no. SB20(20-40)CT model no. 4.

Label says to use Challenger type A, type C , HAGF, and GFCB breakers. box label

Looks like I currently have a mix of type "MM/MH" single and dual pole (type A? These seem to have the side clips) and Type "MP-C" dual pole (back clips). Here's some images: panel with cover off MP-C type breaker type MM/MH breaker MM/MH removed MM/MH type back side

I can't seem to find a dual pole 60 amp type A (side clips) breaker anywhere (max I can find is 50 amp).

I have an Eaton 60 amp type MP/C dual pole. If I move the one 20 amp down type A breaker down above the other 20 amp type a breaker, then can I put the dual pole 60 amp type BR/C breaker in the open space?

Side note: I've read the old challenger type C breakers are a fire hazard (?!) - are these crouse hinds breakers okay, or do they need to be replaced?

Note: updated with more info and pictures.

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    Not an expert but the name challenger seem familiar. A search found this question which might help. diy.stackexchange.com/questions/188609/…
    – crip659
    Commented May 27, 2023 at 19:53
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    Been there done that. So I gave up and now use my Dryer outlet. 30 Amps running at 24 Amp load providing 20 miles per hour or 200 Miles overnight.
    – Traveler
    Commented May 27, 2023 at 20:16
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    Does this answer your question? Replacing a Challenger breaker with an after-market breaker Seems like you should be able to find a BR260 that’s also marked C260. Don’t forget to do the load calculation to verify you can support a new 48A load. Consider telling the EVSE to use a smaller circuit size if you don’t really need to charge at 48A.
    – nobody
    Commented May 27, 2023 at 20:20
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    Also nearly every breaker currently installed is inappropriate for your panel. Crouse-Hinds type MP, MH, etc. are not suitable for the Challenger bus. diy.stackexchange.com/questions/248448/…
    – nobody
    Commented May 27, 2023 at 21:11
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    So much misinformation in the EV space, I could scream. Start with an inoculation [here, at 28:15]. You're like "I want it coz I can have it" you can't (unless you cheat*). You need to do a proper NEC Article 220 Load Calculation on that panel and see what you have to spare, and that's probably plenty for real-world needs for anyone who'd consider an EV. Backed with DC fast charging for actual travel. Commented May 27, 2023 at 21:19

1 Answer 1


The panel and breaker issues are covered elsewhere.

60A charge rate is absolutely bonkers, and is not even slightly any kind of "need". It's like range anxiety - people were driven crazy by it, then it turned out to be a nothingburger. Listen to the experts here - I'm cuing up to 28:15.

Unless the circuits in this panel are largely disused, I see no earthly way 60A is possible here... unless we "cheat" by using EVEMS or a load shed. 20A might happen depending on the NEC Article 220 Load Calculation, and that's enough for most everyone.

The NEC Article 220 Load Calculation

Unless your city offers a different formula, this is the mandatory method (well, 2 methods). Though sometimes your city offers another one. I mention that because people always want to freestyle a new method :) and they always work out in their favor :)

The results of the Load Calc will give you a number. Convert it to amps, and that + EV breaker is your limit.

Most EVSEs have a commissioning procedure using DIP switches or other method to configure the breaker size. (It then tells the car 80% of that figure as the maximum safe amps. That is how EV charging works, which catches many people off guard, since it is a rather new concept). This commissioning procedure allows an EVSE to go on any size of circuit, to be set at installation time. Read the instructions for the procedure, which is UL approved.

Note that cars and some EVSEs have a soft setting to limit amps. If you can do it from the driver's seat, or your easy chair with an app, that is not the correct procedure.

That "cheat", though

When SAE designed the J1772 EV charging system (for the fourth time), they knew a service upgrade was going to be a show-stopper for many sales. Their members are automakers, so they're in it to sell cars :) They foresaw the ability to do demand-side management, so they built the "EVSE tells the EV how much current it can take” tech in the design.

So the EVSE simply needs clamp ammeters on the supply wires to see amps in-use, and it is set with maximum safe amps. It can compute the difference and tell the EV to draw that.

When this type of UL approved system is set up, it makes the EV disappear entirely from the Load Calculation. We don't even need to run the Load Calc, really.

A blunt, ham-handed way to do the same thing is to have a dumb load shed device do the same thing, but have a huge contactor that hard-disconnects the EVSE when there is not 60A of headroom on panel load. This also means the EVSE is simply stone dead, and you cannot interact with it via notifications or an app. This old tech is suitable for hot tubs, water heaters, and other "dumb" storage loads, preferably not an inductive load like a car charger, which will kick big voltage spikes and degrade contactors. But makers of these products have been quick to slap EVEMS labels on them, even though they are old tech.

EVs have a shutdown procedure. It only takes a few milliseconds, but it involves the EV suspending charge using silicon switching, and only then contactors opening. This spares the contactors from arc damage.

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    Eh, I would call a car charger likely a somewhat capacitive load Commented May 28, 2023 at 2:36
  • @ThreePhaseEel the teardowns I've seen of EV chargers (onboard units) involve huge chokes potted into the water cooling channels, because cooling is that critical for them. I'm not a switching power supply designer, but I figure if that is not discharged according to plan, it could be harmful to the contactors and/or the electronics. Commented May 28, 2023 at 23:43
  • Hm. Are you sure the chokes are before any capacitors on the DC bus? Commented May 29, 2023 at 4:17

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