What Does Interrupting Rating Mean on a Circuit Breaker?
Published: 2025-06-13 | 6 min read | Category: Technical Guide
Interrupting rating (also called AIC — Ampere Interrupting Capacity) is the maximum fault current in amperes that a circuit breaker can safely interrupt without exploding, welding shut, or failing to clear the fault. For example, a breaker with a 10,000 AIC rating can safely interrupt up to 10,000 amperes of fault current. If the available fault current exceeds the breaker's interrupting rating, the breaker may fail catastrophically — potentially causing an arc flash explosion, fire, or electrocution.
NEC Section 110.9 requires that every overcurrent protective device have an interrupting rating equal to or greater than the available fault current at its terminals. Violating this requirement is one of the most dangerous electrical code violations because the consequences of failure are immediate and severe — the IEEE estimates that arc flash incidents injure 2,000+ workers per year in the US.
Interrupting Ratings by Breaker Type
| Breaker Category | Typical Interrupting Rating | Application | |---|---|---| | Residential (QO, BR, QP) | 10,000 AIC | Single-family homes | | Enhanced residential | 22,000 AIC | Homes near transformers | | Light commercial (QOB, BQD) | 22,000-42,000 AIC | Small commercial, retail | | Commercial MCCB | 25,000-65,000 AIC | Office buildings, schools | | Industrial MCCB | 65,000-100,000 AIC | Manufacturing, data centers | | Air circuit breakers | 100,000-200,000 AIC | Utility substations, heavy industry |
**Key takeaway:** Higher interrupting ratings are always acceptable — a 65kAIC breaker works fine where 10kAIC is required. But a lower rating than the available fault current is a code violation and a safety hazard. When in doubt, use a higher-rated breaker.
How to Determine What Rating You Need
For residential installations, 10,000 AIC is adequate for most homes. The exception is homes within 25 feet of the utility transformer, where available fault current can exceed 10,000A — these need 22,000 AIC breakers.
For commercial and industrial, a short circuit analysis (fault current study) by a licensed engineer is required. This calculates available fault current at every point in the system based on transformer size, conductor impedance, and distance.
AllBreakerSales.com stocks breakers across the full range of interrupting ratings — from 10kAIC residential to 200kAIC industrial. Call **(877) 611-0034** for help matching the correct interrupting rating to your system requirements.
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Frequently Asked Questions
What happens if a circuit breaker's interrupting rating is too low?
If a fault current exceeds the breaker's interrupting rating, the breaker may fail to interrupt the fault safely. This can result in an arc flash explosion, fire, or destruction of the breaker and surrounding equipment. This is a serious safety hazard — the interrupting rating must always meet or exceed the available fault current at the installation point.
What is the difference between interrupting rating and ampere rating?
The ampere rating is the continuous current the breaker carries under normal conditions. The interrupting rating is the maximum fault current the breaker can safely interrupt. These are completely different parameters — a 100A breaker with a 65kA interrupting rating carries 100A normally but can interrupt a 65,000A fault.
How do I find the available fault current at my panel?
The available fault current is determined by the utility transformer size, the impedance of the transformer and service conductors, and the distance from the transformer. A licensed electrician or electrical engineer can calculate the available fault current using a short-circuit study. The utility company can also provide the available fault current at the service entrance.