Fault Current

[guschash]

Trying to understand fault current. If the main breaker is rated for say 27000 fault current amps ,does all the other breakers in panel have to be rated at 27000 amps as well ?

 

[augie47]

Not necessarily (or normally).. breakers can be "series rated" where downstream breakers have a lower AIC rating.
Here's a good article:

Series Combination Rating Requirements

iaeimagazine.org

 

[don_resqcapt19]

The rating of the main breaker does not tell you the actual available fault current.

The downstream breakers must have an AIC rating at least equal to the available fault current at the line side of those breaker, of be, as Gus said, a listed series combination system.