chuck wrote:
: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?

Many circuit breakers have two tripping method. There's a magnetic
breaker that trips nearly instantly on large overcurrent. Then
there's a thermal breaker that will trip on smaller overload, but not
instantly. That allows for starting motors and the like.