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

jar546

jar546

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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.
 
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jar546 said:
No responses, tells me no one is enforcing this critical code requirement.
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It is early on a Saturday.

As an inspector I would not be plan checking electrical drawings. Qute often, nobody knew what the AIC was until I asked them to find out what it was. Many times they did not know what AIC stood for. Edison acted like I was a problem. The contractors would sometimes point out what was there previously as substantiation. The previous gear might be fifty years old and the environment was altered a half dozen times. The first that they hear about this is when you ask for a placard.

110.24 Available Fault Current.
(A) Field Marking. Service equipment at other than dwelling units shall be legibly marked in the field with the available fault current. The field marking(s) shall include the date the fault-current calculation was performed and be of sufficient durability to withstand the environment involved. The calculation shall be documented and made available to those authorized to design, install, inspect, maintain, or operate the system.

Informational Note No. 1: The available fault-current marking(s) addressed in 110.24 is related to required short-circuit current and interrupting ratings of equipment. NFPA 70E-2018,Standard for Electrical Safety in the Workplace, provides assistance in determining the severity of potential exposure, planning safe work practices, and selecting personal protective equipment.

Informational Note No. 2: Values of available fault current for use in determining appropriate minimum short-circuit current and interrupting ratings of service equipment are available from electric utilities in published or other forms.
 
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Even with clear NEC and IRC requirements, AIC rating verification still gets skipped far too often. The most common reason I hear is that “the equipment is UL listed, so it must be fine.” That is a dangerous assumption. UL listing only confirms that the device can perform at its listed interrupting rating, not that the rating matches the actual fault current at your service location.

The utility company is the starting point for accuracy. Without real fault current data from the power company’s engineering department, any calculation is a guess. This is especially important when:
  • A building is near a new or upgraded utility transformer (lower impedance means higher available fault current).
  • Large on-site motors or generators can feed fault current back into the system.
  • Services are upsized or relocated, changing conductor impedance and thus fault current levels.
Another overlooked issue is cumulative hazard. If an undersized AIC device survives one event without total failure, it may still have sustained internal damage that weakens its ability to trip in future events. That means the “next fault” could be the one that results in catastrophic failure.

TBCF Take: No plan review should be approved, and no service inspection should pass, without confirming that the installed overcurrent protective device interrupting rating equals or exceeds the available fault current. The code has been clear for decades; the gap is in enforcement. Closing that gap is how we prevent the next arc flash disaster.
 
Worth noting is the distance from equipment that is required before you are safe. If enough energy is released, the air can become ionized and you can be electrocuted. Ionization of the air during an arc flash creates a highly conductive plasma, amplifying the arc’s intensity, duration, and destructive potential, making it a more hazardous event.
 
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ICE said:
Worth noting is the distance from equipment that is required before you are safe. If enough energy is released, the air can become ionized and you can be electrocuted.
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Absolutely, which is why 110.26 is so essential, I have been shocked a few times, and it is not fun. In one instance, just getting my knuckles close to the 480V buss while changing a contactor, I was able to start to feel the electricity without even touching anything.
 
Try a 480 contactor inside unit when you are soaking wet with sweat, and do not even touch the contactor. When it was all said and done, and I got my wits back, I was soaked with another type of liquid. Not fun
 
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