Breaker ratings?

[gadero]

I've seen more than one client's standard requiring 22kAIC breakers on all 208Y/120V systems. 10k breakers are unacceptable. When asked why - I've always heard "That's the way we've always done it," or "It's our standard." Is there a good reason (or any reason) for this requirement?

Thanks

 

[jghrist]

One reason might be to allow future increases in transformer size without replacing the breakers. You might get by with 10 kA breakers with a 5% impedance 150 kVA transformer. If the load increased in the future to require a 300 kVA transformer, you would be in trouble.

 

[alehman]

Plan carefully though. 22kAIC breakers are expensive compared to 10k.