Peter Walsh, PE
What is AIC? It's the Amps Interrupting Rating for the panelboard and the panel circuit breakers. This number is typically 10kA (10,000 amps) or 22kA for common panelboards and breakers and even up to 200kA for some. The AIC rating is the maximum number of surge amps that a utility can provide to the equipment and still have the equipment safely trip off.
This rating is in addition to the sustained current rating which could be 200 or even 1200 amps. This AIC rating is a safety rating that is independent of the nominal load rating of the panel.
Section 110.9 of the National Electrical Code requires the equipment rating always to be equal or more than the available surge current. If the equipment has a rating below the potential surge current, it could become a hazard. Unfortunately the higher AIC ratings do cost more.
When using a panelboard for special conditions, the regulations require labeling the AIC for the specific application. The same panelboard might be used for different AIC ratings. This results in multiple AIC ratings on the same panelboard label.
Using circuit breakers of different AIC ratings in the same panelboard causes the most common variation. Many times a panelboard has a rating that is limited to the lowest AIC rated circuit breaker in place. For example, let’s consider an existing panelboard with a 22kA AIC rating with all installed circuit breakers having an equal rating. If you were to install an additional breaker with a 10kA AIC rating, the entire panelboard rating would decrease to the 10kA AIC rating. This is why you can see multiple AIC ratings on panelboards.
Photo courtesy of Square D