Understanding AIC Ratings on Circuit Breakers

Published: 2025-06-23 | 10 min read | Category: Technical Guide

AIC (Ampere Interrupting Capacity) is the maximum fault current a circuit breaker can safely interrupt — measured in amperes at a specific voltage. A breaker rated 22,000 AIC at 240V can safely clear a 22,000-amp short circuit without exploding, welding shut, or failing to interrupt the fault. If the available fault current exceeds the breaker's AIC rating, the breaker will fail catastrophically, potentially causing an arc flash explosion with temperatures exceeding 35,000°F and blast pressures that can throw a worker across a room.

NEC Section 110.9 makes this a hard legal requirement: "Equipment intended to interrupt current at fault levels shall have an interrupting rating not less than the nominal circuit voltage and the current that is available at the line terminals of the equipment." Violating this requirement is one of the most dangerous code violations because the consequences are immediate and catastrophic — not gradual.

AIC Ratings by Breaker Category

| Breaker Type | Standard AIC Rating | Enhanced AIC Rating | Typical Application | |---|---|---|---| | Residential (QO, BR, QP) | 10,000 AIC | 22,000 AIC | Single-family homes | | Light commercial (QOB, BQD) | 22,000 AIC | 42,000 AIC | Retail, small office | | Commercial MCCB (FD, ED) | 25,000 AIC | 35,000 AIC | Office buildings | | Commercial MCCB (HFD, HED) | 42,000-65,000 AIC | — | Schools, hospitals | | Industrial MCCB (JD, HJD) | 65,000 AIC | 100,000 AIC | Manufacturing | | Air circuit breakers | 65,000-200,000 AIC | — | Utility, heavy industry |

**Key takeaway:** You can always use a breaker with a HIGHER AIC rating than required (a 65kAIC breaker works fine where 10kAIC is needed). But you can NEVER use a lower rating than the available fault current — that's a code violation and an explosion risk.

How to Determine Available Fault Current

Available fault current depends on three factors: utility transformer size (larger = more fault current), conductor size and length (longer runs = more impedance = less fault current at the panel), and system voltage.

For residential: most homes have 10,000-22,000A available at the main panel. Homes within 25 feet of the utility transformer can exceed 10,000A, requiring 22,000 AIC breakers.

For commercial/industrial: a short circuit analysis (fault current study) by a licensed engineer is required. This calculates available fault current at every point in the distribution system.

| Transformer Size | Approximate Available Fault Current (480V) | |---|---| | 75 kVA | 2,500A | | 150 kVA | 5,000A | | 500 kVA | 15,000A | | 1000 kVA | 28,000A | | 2000 kVA | 50,000A | | 2500 kVA | 65,000A |

Series-Rated Systems

Series rating allows a downstream breaker with a lower AIC rating to be protected by an upstream breaker with a higher rating — but ONLY in UL-tested combinations. For example, a 65kAIC main breaker can protect downstream 22kAIC branch breakers in a tested series-rated combination, even if the available fault current is 40,000A.

This is common in commercial panels where the main breaker has high AIC and branch breakers have lower (less expensive) ratings. The combination must be UL listed — you cannot assume series rating without manufacturer documentation.

What Happens When AIC Is Exceeded

When fault current exceeds a breaker's AIC rating, the breaker cannot interrupt the arc. The result is: sustained internal arcing at 10,000-35,000°F, vaporization of copper contacts (creating conductive plasma), potential housing rupture (explosion), and arc flash/blast that can cause severe burns, blindness, and death at distances up to 10 feet.

The IEEE estimates 2,000+ arc flash injuries per year in the US, with a significant portion caused by inadequately rated overcurrent protection devices.

AllBreakerSales.com stocks breakers across the full AIC range — from 10kAIC residential to 200kAIC industrial. Call **(877) 611-0034** to verify the correct interrupting rating for your application.

Shop These Breakers

Popular models available for immediate shipping:

• Square D HJA36020 (65kAIC)
• Eaton HFD3100 (65kAIC)

Call **(877) 611-0034** for pricing on any circuit breaker in our inventory.

Frequently Asked Questions

What does AIC mean on a circuit breaker?

AIC stands for Ampere Interrupting Capacity. It's the maximum fault current (in amperes) that the breaker can safely interrupt without failing. For example, a breaker rated 10kAIC can safely interrupt up to 10,000 amperes of fault current. This rating is separate from the breaker's normal current rating (like 20A or 100A).

What AIC rating do I need for residential?

Most residential installations require 10,000 AIC (10kAIC), which is the standard rating for residential breakers like Square D QO, Eaton BR, and Siemens QP. However, if your electrical panel is within 25 feet of the utility transformer or if the transformer has been recently upgraded to a larger size, you may need 22,000 AIC breakers.

Can I use a higher AIC rated breaker than required?

Yes, absolutely. Using a breaker with a higher AIC rating than the available fault current is always acceptable and provides an extra margin of safety. There is no downside to over-rating. For example, using a 22kAIC breaker where 10kAIC would suffice is perfectly fine and may be wise if the utility could upgrade the transformer in the future.

What happens if AIC rating is too low?

If a fault occurs and the available fault current exceeds the breaker's AIC rating, the breaker may fail catastrophically. The contacts can weld together (preventing the breaker from opening), the housing can explode from arc energy, or the breaker may fail to clear the fault — allowing sustained arcing that can cause fires, equipment damage, and serious injury.

How do I find the available fault current at my panel?

For residential, the available fault current is typically 5,000-22,000A depending on transformer size and distance. For commercial and industrial, a short circuit analysis (fault current study) must be performed by a licensed engineer. This study calculates the available fault current at every point in the electrical system based on transformer ratings, conductor sizes, and distances.