How to Read a Circuit Breaker Part Number: A Simple Guide
If you’ve ever looked at a circuit breaker part number like HFD3125, EDB34030, or PDG23M0050TFFJ, you know they can seem like a random collection of letters and numbers.
In reality, manufacturers use part numbers to communicate important information about a breaker, including its frame size, amperage, number of poles, interrupting rating (AIC), voltage, and other features.
Learning how to interpret these model numbers can help you:
- Find the correct replacement breaker
- Avoid costly ordering mistakes
- Compare replacement options
- Determine compatibility
- Save valuable downtime during repairs
Let’s break it down.
Every Manufacturer Uses Its Own Naming System
One important thing to understand is that there is no universal circuit breaker numbering system.
Each manufacturer has developed its own method for identifying products.
For example:
- Eaton
- Siemens
- Schneider Electric
- ABB
- GE
- Mitsubishi
- Fuji
- Allen-Bradley
…all use different formats.
Fortunately, most follow similar principles.
Generally, a part number tells you several key characteristics of the breaker.
1. The Letter Prefix Usually Identifies the Frame
The letters at the beginning typically indicate the breaker family or frame size.
Examples include:
|
Part Number |
Frame |
|---|---|
|
EDB34030 |
EDB Frame |
|
HFD3125 |
HFD Frame |
|
JDB3200 |
JDB Frame |
|
FD3200 |
FD Frame |
|
PDG23M0050TFFJ |
Power Defense PDG2 |
The frame determines many physical characteristics, including:
- Physical size
- Mounting style
- Maximum amp rating
- Available accessories
- Internal design
Important: Two breakers with the same amperage may not be interchangeable if they belong to different frame families.
2. The Numbers Often Indicate the Number of Poles
Many manufacturers include the pole count early in the model number.
Examples:
|
Part Number |
Poles |
|---|---|
|
HFD2125 |
2 Pole |
|
HFD3125 |
3 Pole |
|
EDB34030 |
3 Pole |
|
FD4100 |
4 Pole |
Always verify this using the manufacturer’s specifications, as numbering conventions vary.
3. The Last Numbers Usually Represent the Amp Rating
This is often the easiest portion to recognize.
Examples:
|
Part Number |
Amp Rating |
|---|---|
|
HFD3100 |
100 Amp |
|
HFD3125 |
125 Amp |
|
HFD3200 |
200 Amp |
|
EDB34030 |
30 Amp |
|
FD3400 |
400 Amp |
Although many manufacturers use this convention, not every part number follows the same format. When in doubt, check the published specifications.
4. Interrupting Rating (AIC) May Be Hidden in the Model Number
One of the most important specifications is the interrupting rating, also known as AIC (Ampere Interrupting Capacity).
This tells you the maximum fault current a breaker can safely interrupt.
For example:
- 18 kA
- 22 kA
- 35 kA
- 65 kA
- 100 kA
Higher AIC breakers can often replace lower AIC versions within the same breaker family and frame, provided all other ratings and manufacturer requirements are met. The reverse is not true—you should not substitute a breaker with a lower interrupting rating than the application requires.
Because AIC is critical for safety and code compliance, always verify the replacement against the manufacturer’s documentation and the equipment’s required fault-current rating.
5. Voltage Ratings Matter
Many breakers look identical but have different voltage ratings.
Examples include:
- 240 VAC
- 480 VAC
- 600 VAC
- DC applications
Never assume two breakers are interchangeable based on appearance alone.
6. Some Letters Indicate Special Features
Manufacturers may include additional letters to identify optional features, such as:
- Electronic trip units
- Thermal-magnetic trip units
- Ground fault protection
- Shunt trips
- Undervoltage releases
- Switching duty ratings
- HACR ratings
- Current-limiting designs
These suffixes vary by manufacturer, making it important to reference the correct documentation when replacing a breaker.
Example: Decoding an Eaton HFD3125 Breaker
Let’s use a real-world example.
HFD3125
|
Portion |
Meaning |
|---|---|
|
HFD |
Breaker family/frame (H is the higher AIC version of this frame @65KA) |
|
3 |
Three poles |
|
125 |
125 Amp rating |
From the complete specifications, you would also confirm:
- Voltage rating
- Interrupting capacity (AIC)
- Mounting style
- Terminal/lug configuration
- Trip characteristics
- Required accessories
The model number gives you a strong starting point, but the specification sheet provides the complete picture.
Why Two Breakers with the Same Amp Rating May Not Interchange
This is one of the most common mistakes we see.
For example:
- HFD3125
- JDB3125
- EDB3125
All may be 125-amp, three-pole breakers, yet they can differ in:
- Physical dimensions
- Bus connections
- Mounting method
- Interrupting rating
- UL listings
- Internal design
Selecting a replacement based only on amperage can result in an incompatible or unsafe installation.
Still Can’t Identify Your Breaker?
Don’t worry—many older breakers have faded labels, obsolete model numbers, or discontinued product lines.
At Essential Parts, our team helps customers identify replacement breakers every day.
Whether you’re replacing an obsolete breaker or verifying compatibility before ordering, we’re here to help.
Simply provide:
- A part number
- A photo of the breaker
- The equipment nameplate
- Or any available markings
We’ll help you identify the correct replacement as quickly as possible.
Shop Circuit Breakers with Confidence at Essential Parts
Essential Parts stocks thousands of new, surplus, and obsolete circuit breakers from leading manufacturers, including Eaton, Siemens, Schneider Electric, ABB, GE, Cutler Hammer, and more.
Whether you’re replacing a single breaker or sourcing critical spares for a facility, our team can help you find the correct part quickly and accurately.
- Over 70,000 electrical products in stock
- Fast shipping from multiple U.S. warehouses
- Expert product identification assistance
- Hard-to-find and discontinued components
- Competitive pricing on genuine electrical equipment
Browse our inventory at EssentialParts.com, or contact our team for help identifying your next replacement breaker.
