What Is Interrupt Rating (kA) on a Circuit Breaker?

What Is Interrupt Rating?

The interrupt rating is the maximum fault current (in amperes or kiloamperes) that the breaker can safely interrupt without being destroyed. It is expressed in kA (kiloamperes) or in amperes (e.g., 10,000A = 10kA).

When a short circuit occurs, the fault current can be enormous — far larger than the breaker's normal trip rating. A 20-amp breaker might need to interrupt 10,000 amps of fault current during a short circuit. If the fault current exceeds the breaker's interrupt rating, the breaker can fail catastrophically — exploding, catching fire, or welding its contacts shut.

Common Interrupt Ratings

Residential breakers: Standard: 10kA (10,000A) — adequate for most residential applications High-interrupting: 22kA — used near the service entrance or in high-fault areas

Commercial/industrial breakers: 14kA, 18kA, 22kA — light commercial 35kA, 42kA, 65kA — industrial distribution 85kA, 100kA, 200kA — main service and switchgear applications

How to Determine the Required Interrupt Rating

The required interrupt rating depends on the available fault current at the point of installation. This is determined by:

1. The utility transformer size and impedance 2. The distance from the transformer to the panel 3. The wire size and length

Available fault current is highest at the service entrance (closest to the transformer) and decreases as you move farther into the system. A licensed electrician or engineer can calculate the available fault current using the utility's transformer data.

What Happens If the Interrupt Rating Is Too Low?

If a fault occurs that exceeds the breaker's interrupt rating, the breaker may: Explode or catch fire Weld its contacts shut (failing to interrupt the fault) Damage the panel and surrounding wiring Create an arc flash hazard for anyone nearby

This is why interrupt rating is a critical safety specification — not just a marketing number.

Interrupt Rating vs. Ampere Rating

These are two completely different specifications:

Ampere rating (e.g., 20A): the maximum continuous current the breaker will carry before tripping Interrupt rating (e.g., 10kA): the maximum fault current the breaker can safely interrupt

A 20-amp breaker with a 10kA interrupt rating will trip at 20 amps under normal conditions, but can safely interrupt up to 10,000 amps during a fault.