Understanding circuit breaker frame sizes is essential for proper selection, replacement, and panel compatibility. This guide covers all standard NEMA frame sizes from A-Frame (smallest) through L-Frame (largest), with amperage ranges, physical dimensions, and brand-specific catalog number patterns.
The frame size determines the physical dimensions of the breaker and its maximum continuous current rating. A breaker's trip rating can be set at or below the frame rating, but never above it. Frame sizes are standardized across manufacturers, so a D-Frame breaker from Square D fits the same panel space as a D-Frame from Siemens.
| Frame | Max Amps | Typical Voltage | Poles | Common Applications |
|---|---|---|---|---|
| A-Frame | 100A | 240V | 1-3 | Residential panels, light commercial |
| B-Frame | 100A | 480V | 1-3 | Small commercial panels |
| C-Frame | 150A | 480V | 2-3 | Commercial distribution |
| D-Frame | 250A | 600V | 2-3 | Industrial switchgear |
| E-Frame | 250A | 480V | 3 | Industrial motor circuits |
| F-Frame | 400A | 600V | 3 | Large industrial feeders |
| G-Frame | 400A | 600V | 3 | High-interrupting applications |
| H-Frame | 150A | 600V | 3 | Industrial branch circuits |
| J-Frame | 400A | 600V | 3 | Large feeders, main breakers |
| K-Frame | 600A | 600V | 3 | Main distribution, large motors |
| L-Frame | 2500A | 600V | 3 | Main switchgear, utility entrance |
Square D uses letter prefixes in catalog numbers: HJA (H-Frame), JDA/JGA (J-Frame), KA/KH (K-Frame), LA/LH (L-Frame), EDB (E-Frame). Browse all Square D breakers.
Eaton frame sizes follow the FD, GHB, HFD, JD, KD, LD pattern. The first letter(s) indicate frame. Browse all Eaton breakers.
Siemens uses ED, FD, HFD, JD, LD, MD prefixes. The frame letter is typically the second character. Browse all Siemens breakers.
GE breakers use TH (miniature), SF, SG, SK, SL prefixes for industrial frames. Browse all GE breakers.
Most manufacturers encode the frame size in the first 2-3 characters of the catalog number. For example, Square D HJA36020 = H-Frame, J-type, A-series, 3-pole, 600V, 20A. Use our Cross-Reference Tool to decode any catalog number.
Select a frame size based on: (1) the maximum current your circuit may carry, (2) the available voltage, (3) the interrupt rating required by your installation, and (4) the physical space in your panel or switchgear. When in doubt, call (877) 611-0034 and our specialists will help you select the correct frame.