On Sun, 29 Jan 2017 16:39:41 -0500, wrote:

On Sun, 29 Jan 2017 15:46:51 -0500, wrote:

From the typical curves I've seen, a 200A breaker will trip in minutes
or less at 295.


I'm thinking that was a typo and should have been 205.
More likely it was supposed to read 195.

Why would a 200a breaker ever trip with 195a?
After a long time at full load, if the ambient temperature increases,
it CAN trip below the rated current. Since all of the breakers contain
thermal trip mechanisms, they do produce heat - so if the box cannot
shed the extra heat, it will get warm. If it gets warm enough the main
breaker is de-rated.

All of the breakers are supposed to be de-rated to 80% for continuous
load - so a 30 amp breaker should not be loaded above about 25 amps
continuous load.

I know there is a lot of conroversy over the 125% load calculation
(which is effectively an 80% load limit) - but if he is loading every
breaker to 100% of it's rated protection current, and the total
current ratings of the breakers in use = 100% of the main breaker
rating, he's REALLY pushing things. If he has a 100% load rated main
breaker in a 100% rated enclosure, the extra heat is being dissipated
and accounted for - but you can be pretty well assured he does NOT
have a 100% rated enclosure and the panel is likely inside a closet
where it does not shed heat effectively.