The circuit breaker is there only to protect the wire it is connected to.
Manufacturers generally estimate the breaker size to trip when the
appliance is drawing enough current that it is toast. (pun intended)


Aaron Coolidge wrote:
Mike Rapoport wrote:
: OK this makes sense. I had not considered that the breakers might not trip
: because of the resistance of the wire feeding the bus during the overload.
: I suppose that there is also the tolerances of the breakers to be
: considered. Thanks!

Hi Mike. These breakers that we have have a fairly complex trip curve.
Potter & Brumfield make the majority of breakers, looking at their web site
will probably turn up a document on how the breakers actually work.

In general, a breaker MUST carry about 110% rated without tripping. At 140%
rated current the trip time us usually measured in hours. 200% rated gets
you into minutes before the breaker trips. 500% rated it should trip in
milliseconds.