How to Read a Circuit Breaker Label

Ampere Rating (Ampacity)

The most prominent number on any circuit breaker is its ampere rating — the maximum continuous current the breaker is designed to carry without tripping. Common residential ratings are 15A, 20A, 30A, 40A, 50A, and 60A. Commercial and industrial breakers range from 15A to 6,000A.

The ampere rating is always stamped in large numerals on the handle or face of the breaker. On molded case circuit breakers, it may appear as "100A" or just "100".

Voltage Rating

The voltage rating tells you the maximum system voltage the breaker can safely interrupt. Common ratings:

120/240V AC: standard residential single-phase 240V AC: 2-pole residential 480Y/277V AC: commercial 3-phase wye 600V AC: industrial 125/250V DC: DC applications

A breaker rated for 480V can be used on 240V systems, but a 240V breaker must never be used on a 480V system.

Interrupt Rating (AIC or kAIC)

The interrupt rating — expressed in amperes interrupting capacity (AIC) or kiloamperes (kAIC) — is the maximum fault current the breaker can safely clear without being destroyed. This is one of the most important and most overlooked specifications.

Common interrupt ratings: 10,000 AIC (10 kAIC): standard residential 22,000 AIC (22 kAIC): commercial residential 65,000 AIC (65 kAIC): commercial/industrial 100,000 AIC (100 kAIC): high-fault industrial

The interrupt rating must equal or exceed the available fault current at the point of installation.

Number of Poles

The number of poles is usually indicated by "1P", "2P", or "3P" on the label, or by the physical width of the breaker. Some labels use "1-pole", "2-pole", or "3-pole".

1-pole: controls one hot conductor, 120V circuits 2-pole: controls two hot conductors, 240V circuits 3-pole: controls three hot conductors, 3-phase circuits

Catalog Number

The catalog number (also called part number or model number) uniquely identifies the exact breaker. It encodes the series, frame size, amperage, poles, and sometimes the interrupt rating and trip type. For example:

QO120: Square D QO series, 1-pole, 20A HFD3100: Eaton HFD series, 3-pole, 100A JDA36070: Square D JDA series, 3-pole, 70A, 65kAIC

The catalog number is what you need when ordering a replacement.

UL Listing Mark

The UL (Underwriters Laboratories) listing mark confirms the breaker has been tested and certified to UL 489 (for branch circuit breakers) or UL 1077 (for supplementary protectors). Always verify the UL listing when purchasing replacement breakers — unlisted breakers may not provide adequate protection.

Series and Frame Size

Industrial breakers include the frame size on the label — typically expressed as a current rating (e.g., "100A frame", "250A frame", "600A frame"). The frame size determines the physical dimensions and the maximum ampere rating available in that frame. A 70A breaker in a 250A frame can be upgraded to 250A by changing the trip unit, without replacing the entire breaker body.