When sizing a circuit breaker, is it fair to say: multiply the calculated amperage by 1.25 and, if necessary, round up?
Thanks in advance,
Jim Finley

gernally yes but a catch is it depend on the conductor as well

devices 800 amp and over

where the over current device is rated 800 amp and over the conductors ampcity it protected shall be equal or greater than rating of conductors

device of 800 amp or less
the next stanard overcurrent rating shall be permitted to be used provied all the following condtion are met:

1] the conductors being protected are not part of multioutlet branch circuit supplying for cord and plug connected portable loads

2] the ampacity of the conductors does not corponded with the standard ampre rating of the fuse or circuit breaker without overload adjustment above the ratings

3] the next higher standard rating do not excess of 800 amperes. [ see above ]

merci, marc

[This message has been edited by frenchelectrican (edited 05-02-2006).]

It's simple. Calculate the load (125%+100%), select a cable to carry the load (the cable must carry the calculated load), select a breaker to protect the cable (the breaker is based upon the cable's rated ampacity noting the 800a up/down rule as the other poster pointed out).