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chuck chuck is offline
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First recorded activity by BoatBanter: Nov 2006
Posts: 41
Default Circuit Breaker Trip Amps

GeoffSchultz wrote:
Can someone define what the "trip amps" on a breaker means? I have a
20A breaker that has a Trip Amps of 27A. I'm running a breaker right
at 20A and it's tripping after several minutes. I just increased it
to a 25A breaker, but I'd like to understand what "trip amps" means.

-- Geoff

Hello Geoff,

As you've found out, common circuit breakers are not precision devices.
The current at which a breaker will trip seems to be a function of age,
time, number of switch cycles, manufacturing tolerances, etc. Seems to
usually work out ok, though.

Generally, a 20 Amp breaker will not trip at 20 Amps, at least not
immediately. They are tested at 135% and 200% of rated capacity. So the
27 Amps works out to be 135% of 20 Amps. This is sometimes called a
"must trip" rating, which, in practice, is a must trip if you cross your
fingers thing. After all, do you know anybody who has ever tested one?

Hope that helps.

Good luck.

Chuck

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