According to, say, the Square D documentation, their QO-series mains and breakers don't series-rate for AIC for more than two levels. That is, a 22,000 AIC main with a 10,000 AIC breaker series rates to 22 kAIC for the combination. But, if you have a 22 kAIC main feeding a 10 kAIC breaker feeding a subpanel which contains 10 kAIC breakers, the combination is only rated for 10 kAIC.

In order to keep the 22 kAIC rating, you need to either use a 22 kAIC breaker feeding the subpanel (QOs series rate with other QOs, local or remote), or use only 22 kAIC breakers in the subpanel.

However, judging from the what's on the shelf at the local retail establishments, I infer that this is rarely done. They don't appear to stock 22 kAIC 70-100 amp breakers with which to feed subpanels. Therefore, it appears to me that there are very few residential subpanel installations around that keep the 22 kAIC rating of the main panel.

Am I missing something here? Like, that all residental services are less than 10 kA SCC? Or that the breakers really do series-rate three levels deep? Or that the wiring to the subpanel is (nearly) always sufficient to reduce the available SCC to < 10 kA?

Or is the SCCR requirement just routinely ignored?

[This message has been edited by SolarPowered (edited 07-29-2004).]