What is an AIC Rating and how is it calculated?

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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.

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I found a great Excel worksheet you can use free of charge that does the calculations for you as you enter information.

AIC ratings for circuit breakers are determined by the manufacturer, depending on the electrical and physical strength of the circuit brakers, and then labeled as required by Underwriters Laboratories.

The Excel calculator provided is a simple method of determining what rating the electrical equipment must meet or exceed.

For example, if the first section of calculation was performed, and the result was the available fault current at the terminals of Main Disconnect was calculated to be 12 KAIC, the electrical equipment, specifically circuit breakers, fuses, etc, at that location would need to be rated a minimum of 12 KAIC.

With this information, you then consult with the supplier of equipment and purchase equipment with a rating that meets or exceed that rating.

As an electrical system gets farther away from the Main, the calculated fault current usually gets lower, and downstream equipment may be rated lower AIC.

If a circuit breaker is installed in a system that is rated lower that the available fault current, in the event of a short circuit condition, the device can actually explode into dangerous shrapnel, along with an arc blast, capable of causing injury or death to someone close by, and fire to the surroundings, rather than simply opening normally to de-enegize the circuit.