I have a panel of type XO circuit breakers in my house. One of them has failed closed (!) and I need to replace it.

However, a few minutes on Google seems to indicate that this type of breaker is no longer produced. A few sites sell refurbished ones, but other forums mention that this is also problematic. If I buy a refurb breaker, how do I test it to make sure it is good?

  • As @keshlam mentioned, you should only buy refurbished breakers from an established legitimate breaker dealer who certifies that they have been load tested and offers a guarantee. I would be very surprised if you could find new old stock (NOS) on XO breakers as they have been out of production for years. Commented Sep 2, 2014 at 0:19
  • FYI, there is also a question about testing breakers here. Basically, without special gear you can't. Commented Oct 2, 2014 at 23:17
  • The fact that you've had one breaker fail closed (one of the few things that they are NEVER supposed to do), would make me nervous about the whole panel. Commented Oct 2, 2014 at 23:21

2 Answers 2


While I'm sure the cost seems prohibitive, it might be time to start thinking about changing out the panel. If the breakers are known to fail closed, you could end up watching your home burn to the ground (hopefully from the outside).


The only way to test a circuit breaker is to present it with various loads and see how quickly it pops, and measure whether that matches the formal specifications for that breaker. Theoretically, the folks selling refurbs SHOULD have done exactly that testing, and the manufacturers should have done so at least on samples from the production line... so this becomes a question of now much you are willing to trust your supplier..

Quick tip: I too have a breaker box that takes a format of breaker which is no longer easy to find. However, many houses in my town were (re)wired at about the same time and use the same breaker, so while the major electrical suppliers don't stock these the local hardware stores DO. You might want to check locally before assuming that refurbs are your only option. (My electrician knew this. My solar installer's electrician didn't, and wasted a few hours until someone clued him in.)

  • +1 for the recommendation to just look around. I've never had a problem finding a NOS breaker before.
    – Comintern
    Commented Sep 2, 2014 at 0:04
  • 2
    The suggestion to load the breakers is sketchy at best. I DO NOT recommend this. Breakers do NOT trip at just over the rating. Not even close. For instance, a 20A breaker can run at 22-24 amps probably for hours. Breakers trip on a curve, not as soon as they exceed the rating. Commented Sep 2, 2014 at 1:00
  • I certainly wouldn't try testing it in a house circuit. But if I had to test it, that's how I'd set up the workbench. And I agree that one has to understand what the expected behavior curve is, just as one had to understand the difference between slow-blow and fast-blow fuses. My best advice is to look for a proper replacement. If that fails, my recommendation would be to ask a Proper Electrician about the quality of rebuilds and what he'd do in this situation.
    – keshlam
    Commented Sep 2, 2014 at 1:27
  • 1
    @SpeedyPetey is right, the response time of a breaker depends on the current, it's not a simple on/off switch. There is no way to test a breaker without a serious amount of lab equipment capable of generating thousands of amps and accurately measuring response times down to the hundredth of a second. Additionally, even if you had the equipment it's probably impossible to test a breaker anywhere with standard electrical service because you would blow the main disconnect.
    – Hank
    Commented Sep 2, 2014 at 15:52
  • Hm. I'm willing to believe that. Updating answer.
    – keshlam
    Commented Sep 2, 2014 at 16:20

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