AIC Ratings: The Most Overlooked Yet Critical Safety Check in Electrical Plan Review NEC 110.9

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AIC Ratings: The Most Overlooked Yet Critical Safety Check in Electrical Plan Review​

Building Officials, Plans Examiners, and Inspectors: Are you verifying the AIC rating of service disconnects during plan review? If not, you are overlooking one of the most critical safety requirements in the NEC and IRC—and that oversight could be catastrophic.

Let’s be clear: the interrupting rating (AIC) of a service disconnect must always meet or exceed the available fault current at the service. If it doesn’t, and a fault occurs, the consequences can be severe—breakers exploding, electrical panels disintegrating, arc flashes, or worse, an uncontrolled electrical fire that puts lives at risk.

The Code is Clear—There’s No Excuse for Not Checking This​

Some may try to argue that the IRC is less rigorous than the NEC, but even the IRC mandates compliance with interrupting ratings.

• IRC E3404.2 requires a minimum 10,000 AIC rating, but that is not an automatic approval. It’s a starting point—the equipment must still be rated for the actual available fault current at the service.
• NEC 110.9 is explicit: Equipment must have an interrupting rating at least equal to the available fault current at the line terminals.
• NEC 110.10 goes further, requiring overcurrent protective devices to be coordinated to clear faults without excessive damage.

The key takeaway? The AIC rating must always match or exceed the available fault current. If a plan submission shows an available fault current of 17,500A and the contractor submits a 10,000 AIC service disconnect, that’s an automatic rejection.

What Happens When AIC Ratings Are Ignored?​

Failing to verify AIC ratings isn’t just a code violation—it’s a serious life-safety hazard. Here’s what happens when a fault exceeds a breaker’s AIC rating:

1. The breaker or fuse may rupture instead of clearing the fault. That means instead of stopping the overcurrent, it turns into shrapnel—literally blowing apart the enclosure.
2. An arc flash can occur, sending superheated plasma and molten metal flying. Temperatures can exceed 35,000°F in an instant.
3. The electrical panel or service disconnect can explode, causing severe property damage, injuries, or fatalities.
4. Fire risk skyrockets. The moment an overcurrent protective device fails, the fault continues unchecked, superheating conductors, igniting insulation, and spreading fire through the structure.

If you think this is hypothetical, look up arc flash incidents and failed breaker videos—they’re out there, and they are terrifying. The NEC doesn’t include AIC requirements just to fill space in the codebook. This is a matter of life safety.

Plan Review Must Include AIC Verification​

If you’re approving electrical service upgrades, replacements, or new installations without verifying AIC calculations, you are failing to perform one of the most critical safety checks required by the NEC and IRC.

Here’s what must be done during plan review:

1. Require the contractor to submit an AIC calculation for every service disconnect installation or upgrade.
2. Verify the calculation against the service equipment’s interrupting rating. If the available fault current exceeds the AIC rating, reject it.
3. Ensure that the available fault current data comes from the utility company. This isn’t a guess—it’s based on real-world electrical system conditions.
4. Educate your inspectors. When performing final inspections, they must verify that the installed equipment matches what was approved in the plan review.

No More Excuses—This Must Be Enforced​

There is no excuse for failing to check AIC ratings. It’s not an “optional” review item, and it’s certainly not something to assume is “probably fine.” If a permit applicant is not submitting their AIC calculation, they are not providing a complete application.

As Building Officials, Plans Examiners, and Inspectors, it is our job to enforce the codes that protect people’s lives. Checking AIC ratings is not extra work—it is a fundamental part of electrical safety enforcement. If you are not doing this, you are leaving a massive safety gap in your jurisdiction.

The NEC and IRC demand compliance with proper interrupting ratings. Now, it’s up to us to make sure those requirements are enforced.