Looking for a replacement of the old Murray main breaker

Following the above link, I'm looking to replace an old Murray breaker and I got the answer that the Siemens QN2200H breaker is the proper replacement (Thank you ThreePhaseEel). The old breaker has a tagged rating of 10,000A interrupting current, the suggested new QNH breaker has a tagged rating of 22,000A. The regular QN breaker is rated 10,000A. Is that the more appropriate breaker? I think that's the only difference between QN and QNH? Honestly, I don't understand what these ratings are...thanks in advance!

  • Just a guess but those figures are probably the current needed to jump open contacts(nasty arc welding).
    – crip659
    Jan 5, 2023 at 18:32
  • Who is your electric utility? Jan 6, 2023 at 4:45

1 Answer 1


You have to ask your power company that.
Or your AHJ might know.

When the power company did the wiring to your house, they are required to choose transformers, wires and lengths that would have enough resistance that a dead short at your main breaker could not possibly exceed XXXXX amps. The goal is to make it possible for the main breaker to interrupt current from a dead short across your bus bars. If they hotshot you right off the transformer, with no wire resistance, it might flow a million amps and simply weld the breaker closed - and then nothing would stop the short.

That value is a compromise between that, and the power company not losing a lot of energy from the resistance of those wires. They'd prefer the resistance to be as low as possible but they must follow the state codes on this point (which is not NEC by the way).

Most residential is 10kA (10,000 amps) but some may use 22kA.

More is better. A 22kA breaker is entirely acceptable where 10kA is required.

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