How to Read a Circuit Breaker Label

Published: 2026-07-01 | 7 min read | Category: Technical Guide

Every circuit breaker has a label packed with critical information. Understanding these markings is essential for ordering the correct replacement, verifying code compliance, and ensuring your electrical system is safe. This guide covers every marking you'll find on breakers from Square D, Eaton, Siemens, GE, and other major manufacturers.

The Five Critical Label Markings

Every circuit breaker label contains at least these five pieces of information:

1. **Catalog Number** — the unique identifier for ordering an exact replacement 2. **Ampere Rating** — the continuous current the breaker is designed to carry 3. **Voltage Rating** — the maximum system voltage 4. **Interrupting Rating (KAIC)** — the maximum fault current it can safely clear 5. **UL/CSA Listing Mark** — proof of third-party safety testing

Decoding the Catalog Number

The catalog number is the single most important marking. It encodes everything you need to order a replacement.

Square D Catalog Number Format

Example: **HJA36020**

| Position | Characters | Meaning | |----------|-----------|----------| | 1 | H | High interrupting capacity (65 KAIC) | | 2 | J | J-frame (250A frame) | | 3 | A | Standard thermal-magnetic trip | | 4 | 3 | 3-pole | | 5 | 6 | 600V rated | | 6-8 | 020 | 20 amp trip rating |

Eaton Catalog Number Format

Example: **HFD3100**

| Position | Characters | Meaning | |----------|-----------|----------| | 1 | H | High interrupting capacity | | 2-3 | FD | FD-frame (100A frame at 600V) | | 4 | 3 | 3-pole | | 5-8 | 100 | 100 amp trip rating |

Siemens Catalog Number Format

Example: **HED43B100**

| Position | Characters | Meaning | |----------|-----------|----------| | 1 | H | High interrupting capacity (42 KAIC) | | 2-3 | ED | ED-frame (100A frame) | | 4 | 4 | 480V rated | | 5 | 3 | 3-pole | | 6 | B | Thermal-magnetic trip | | 7-9 | 100 | 100 amp trip rating |

Ampere Rating

The ampere rating is usually the largest number on the breaker face, often printed in bold or on a colored background. Key points:

• **Handle marking** — most breakers have the amperage stamped or printed directly on the operating handle
• **Adjustable trip** — some industrial breakers have adjustable trip settings; the label shows the range (e.g., "70-100A")
• **Sensor rating vs. trip rating** — on electronic-trip breakers, the sensor (frame) rating and the trip setting may differ

Voltage Rating

Voltage ratings indicate the maximum system voltage:

| Label Marking | Meaning | |--------------|----------| | 120/240V | Residential split-phase | | 240V | Single-phase industrial | | 480V | Three-phase commercial | | 480/277V | Three-phase wye | | 600V | Maximum industrial | | 120/240V or 480V | Dual-rated |

Interrupting Rating (KAIC/AIC)

The interrupting capacity is marked in one of these formats:

• **"22,000 AIC"** or **"22 KAIC"** — can interrupt 22,000 amps of fault current
• **"65kA @ 480V"** — 65,000 amps at 480 volts
• **Multiple ratings** — some breakers list different KAIC at different voltages (e.g., "65kA @ 240V, 35kA @ 480V")

Common KAIC Ratings by Application

| Application | Typical KAIC Required | |------------|---------------------| | Residential panel | 10 KAIC | | Small commercial | 14-22 KAIC | | Commercial building | 25-42 KAIC | | Industrial facility | 42-65 KAIC | | Utility/switchgear | 65-200 KAIC |

Trip Type Indicators

| Marking | Trip Type | Meaning | |---------|-----------|----------| | TM or Thermal-Magnetic | Thermal-Magnetic | Standard — thermal element for overloads, magnetic for short circuits | | LSI | Electronic | Long-time, Short-time, Instantaneous adjustable settings | | LSIG | Electronic + Ground | Adds adjustable ground fault protection | | MO or Motor Circuit | Motor Circuit Protector | Magnetic-only trip for motor branch circuits | | GFCI | Ground Fault | Built-in ground fault protection (5mA residential) | | AFCI | Arc Fault | Detects arcing faults for bedroom/living area circuits | | DF or Dual Function | AFCI + GFCI | Combined arc fault and ground fault protection |

UL Listing and Standards

Look for these marks:

• **UL Listed (UL 489)** — standard for molded-case circuit breakers
• **UL 489 Current Limiting** — breaker limits let-through energy during faults
• **UL Listed (UL 1077)** — supplementary protectors (not branch circuit rated)
• **CSA Certified** — Canadian safety certification
• **IEC 60947-2** — international standard (common on imported equipment)

When the Label is Worn or Missing

If you can't read the label:

1. **Check the side of the housing** — catalog numbers are often molded into the plastic 2. **Look inside the panel door** — many panels have a breaker schedule listing catalog numbers 3. **Measure the breaker** — physical dimensions narrow down the frame size 4. **Count the poles and measure the handle** — helps identify the series 5. **Call us** — send a photo to AllBreakerSales.com and we'll identify it for free

Bottom Line

Shop These Breakers

Popular models available for immediate shipping:

• Square D QO120
• Eaton BR230
• Siemens Q230

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

The catalog number tells you everything. If you can read the catalog number, you can order an exact replacement. If you can't, the combination of brand + frame size + poles + amperage + voltage will get you there. Call AllBreakerSales.com at (877) 611-0034 — we identify breakers from photos daily and can match your exact part.

Frequently Asked Questions

Where is the catalog number on a circuit breaker?

The catalog number is typically printed on the front face of the breaker, near the top or center. On Square D breakers, it's on the front label (e.g., HJA36020). On Eaton/Cutler-Hammer, it's on the front or side (e.g., HFD3100). On Siemens, it's on the front face (e.g., HED43B100). If the front label is worn, check the side of the breaker housing — many manufacturers stamp the catalog number into the plastic.

What do the numbers in a breaker catalog number mean?

The catalog number encodes frame size, voltage class, interrupting capacity, number of poles, and amperage. For example, Square D HJA36020: H = high interrupting capacity, J = J-frame (250A), A = standard, 3 = 3-pole, 6 = 600V, 020 = 20 amps. The exact encoding varies by manufacturer, but the last 2-4 digits almost always indicate the amperage.

What does the KAIC number on a breaker mean?

KAIC stands for Kilo Ampere Interrupting Capacity — the maximum fault current (in thousands of amps) that the breaker can safely interrupt. A breaker rated 22 KAIC can clear a fault of up to 22,000 amps. This must be equal to or greater than the available fault current at the panel. Using a breaker with insufficient KAIC is a code violation and safety hazard.