Not all electrical construction projects will have plans or blueprints. There will always be service work, replacement panelboards, adding new circuits and remodel work. For these situations, the electrician has even more responsibility to understand Available Fault Current (AFC), overcurrent device interrupting ratings (AIC ratings), equipment Short-Circuit Current Ratings (SCCR’s) and Series Rated Combinations in order to comply with NEC^® 110.9 and 110.10 and many other code sections in the NEC^® that have similar requirements.

When called to replace or upgrade an existing panelboard or service, several things need to be considered:

• Take note of the AIC ratings of circuit breakers in the existing panelboard. A 65k AIC rated breaker costs at least twice as much as a 10k AIC breaker. If circuit breakers in the panelboard have an AIC rating of more than 10k, it’s likely that there was a reason for it, otherwise, why would the previous electrician who originally installed the panelboard have spent the extra money on the high dollar circuit breakers?
• Step outside and observe how close the utility transformer is to the service panelboard being replaced. If it’s right on the other side off the wall, then it can be assumed that the length of service entrance conductors are relatively short. The shorter the run of wire, the more AFC at the line terminals of the panelboard.
• If adding a new panelboard supplied by a feeder coming from the service panelboard, do a bit of homework before ordering the new panelboard. In order to comply with 110.9, the AFC must be determined where the new panelboard will be installed in order to purchase circuit breakers for the panelboard with the correct AIC rating.