10–30 A
10, 15, 20, 25, 30 A
Common small branch or equipment ratings, depending on system, conductor, load and rules.
Common does not mean interchangeable across panels or markets.
Circuit protection selection guide
What Are the Standard Sizes of Circuit Breakers?
The ampere number is only one part of breaker size. Buyers and maintenance teams must also match the frame, poles, voltage, trip behavior, breaking capacity and physical connection.
Short answer: common U.S. branch ratings include 15, 20, 30, 40, 50 and 60 A, while the current NEC standard series includes values from 10 A through 6,000 A. IEC-style MCBs use their own series and modular formats. A standard ampere value does not make two breakers interchangeable.
10 A to 6,000 ACurrent U.S. standard inverse-time breaker series
7 selection dimensionsAmps alone do not define a compatible device
MCB, MCCB and ACBDifferent construction, duty and physical formats
Panel label controlsPhysical fit is not proof of approved compatibility
Start with the right question
“Breaker size” can mean seven different things
A homeowner often means the handle ampere number. A panel builder may mean DIN-module width. A switchgear buyer may mean frame size. An engineer may mean interruption duty. These answers cannot be substituted for one another.
Do not increase a breaker rating simply to stop tripping. Repeated trips require a load, conductor, connection, fault and protection review.
01
Rated current
The ampere designation or configured long-time rating under stated product conditions.
02
Frame size
The maximum current family or construction envelope, not always the installed trip rating.
03
Poles and voltage
The conductor arrangement and electrical system the device is designed to open safely.
04
Physical dimensions
Width, height, depth, mounting, bus connection, terminals and accessory clearance.
05–07
Trip curve, breaking capacity and product category
How the breaker responds, which fault duty it can interrupt and what protective function it is approved to perform.
Seven meanings of size
Read the complete breaker specification, not one number
Each field answers a separate selection question. A correct replacement must satisfy them together.
| What people call size | What it means | Why it changes the decision |
|---|---|---|
| Ampere rating | Rated current, fixed trip value or configured long-time current. | Must coordinate with the design load, conductor, terminals and applicable installation rules. |
| Frame size | Largest current rating available for a breaker construction or family. | A 250 AF construction may use a lower sensor, rating plug or trip setting, depending on the exact design. |
| Pole count | One, two, three or four mechanically linked breaker elements. | Must match the supply topology, protected conductors and required simultaneous opening. |
| Physical size | Width, height, depth, mounting, bus connection and terminal geometry. | Determines whether the device integrates with the enclosure, busbar and conductor arrangement. |
| Trip characteristic | Thermal, magnetic or electronic response versus current and time. | Changes inrush tolerance, overload response, fault clearing and coordination. |
| Breaking capacity | Fault current the breaker can interrupt under a stated standard, voltage and test condition. | Must be adequate for prospective short-circuit current at the installation point. |
| Voltage and category | AC/DC voltage plus the standard or protective function under which the device is evaluated. | A current-correct device can still be unsuitable for the system voltage or the required branch-circuit role. |
Standard ampere ratings
The U.S. series is broad; the familiar values are only the beginning
For 2023 NEC-based work, Table 240.6(A) includes 10 A as a standard inverse-time breaker rating. The complete series continues through large distribution values. Local adoption and the exact product family still control.
35–125 A
35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125 A
Larger branch, equipment and feeder directions in multiple breaker forms.
The same current can appear in MCB, panel-breaker or MCCB families.150–800 A
150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800 A
Commercial and industrial distribution where frame and trip-unit details become central.
Ask whether the number is frame, sensor, rated current or setting.1,000–6,000 A
1,000, 1,200, 1,600, 2,000, 2,500, 3,000, 4,000, 5,000, 6,000 A
Engineered power-distribution and switchgear applications.
Protection studies, fault duty, coordination and switchgear integration are required.
This is a standard-rating list, not a conductor or appliance chart.
Nonstandard ratings may also be permitted in defined contexts. Availability varies by breaker family, voltage, poles, trip design, breaking capacity, panel system and target-market approval.
Product-family map
MCB, MCCB and ACB use different sizing language
Current ranges overlap, but construction, mounting, adjustment, interruption duty and procurement data are different.
01 / MCB
Miniature circuit breaker
Compact DIN-rail or market-specific panel protection for final distribution and equipment circuits.
- Rated current and B/C/D curve
- Poles, voltage and breaking capacity
- Module width, terminals and busbar system
02 / MCCB
Molded case circuit breaker
Feeder, equipment and distribution protection with larger frames and fixed or adjustable trip systems.
- Frame, sensor and actual current rating
- Icu/Ics or applicable fault-duty values
- Lugs, mounting, accessories and enclosure
03 / ACB
Air circuit breaker
High-current switchboard protection where the complete breaker, cradle, trip unit and accessory configuration matters.
- Frame and rated current
- Fixed or draw-out construction
- Trip settings, interlocks and communication
Frame versus actual rating
A 250 A frame does not always mean a 250 A trip setting
UL defines frame size as the largest ampere rating available for a group of similar molded-case construction. On applicable electronic-trip products, a sensor, rating plug and long-time setting can create a lower usable current rating. The exact relationship is manufacturer-specific.
Conceptual relationship only. It is not a universal ratio and does not represent a SENTOP model. Use the exact trip-unit documentation and approved setting range.
Three decisive ratings
The same ampere rating can behave very differently
Poles and voltage define the system connection. The trip curve defines response. Breaking capacity defines which fault duty the breaker can interrupt under stated conditions.
Requirement builder
Turn a vague size request into a usable technical brief
This tool does not calculate or approve a breaker rating. It shows which information must be collected before a supplier, panel builder or qualified electrical professional can review the requirement.
Start with the panel and circuit data
Select the closest situation, then generate a checklist. The result stays on this page and does not submit any data.
- System voltage and current type
- Load, conductor and fault-current information
- Complete model and compatibility evidence
Selection workflow
Choose from the circuit first, then confirm the physical product
The order matters. Starting from a product photograph or handle number skips the information that determines protection.
Define the circuit function
Branch, feeder, main, motor, control, equipment internal, PV/battery or supplementary protection.
Confirm the system
AC/DC, frequency, voltages, grounding arrangement, source and required pole/neutral treatment.
Establish the design load
Use the applicable code and equipment instructions. Separate continuous duty and inrush where relevant.
Coordinate the conductor
Material, cross-section, installation method, ambient conditions, bundling, terminals and temperature limits.
Determine fault duty
Obtain prospective short-circuit current at the breaker location and the coordination requirement.
Select protection behavior
Trip curve or electronic settings plus required residual-current, arc-fault, motor or DC function.
Confirm integration
Panel family, mounting, bus, terminals, dimensions, accessories, enclosure and target-market approval.
Freeze the model record
Document the full catalog number, ratings, settings, approved sample, labels and order configuration.
Replacement boundary
A breaker that fits can still be the wrong breaker
UL states that field-added breakers must be identified as suitable for the panelboard. Different manufacturers or styles are not identical in all details and may not be interchangeable.
01
Panel make and modelUse the panelboard label and approved breaker list.
02
Complete catalog numberInclude suffixes, trip unit, accessories and pole configuration.
03
Bus and mountingPlug-on, bolt-on, DIN rail, fixed, draw-out or proprietary construction.
04
Terminals and dimensionsConductor range, torque, bending space, width, depth and clearance.
05
Electrical ratingsCurrent, voltage, poles, curve, breaking capacity and required product category.
Buyer and RFQ checklist
Send enough data to quote the correct configuration
“Three pole, 100 A” is not enough. A useful RFQ identifies electrical duty, physical integration and evidence required for the destination market.
Include these fields
- Application: branch, feeder, main, motor, equipment, PV/battery or supplementary protection.
- System: AC/DC, frequency, line-to-line and line-to-ground voltage, grounding arrangement.
- Current duty: calculated load, continuous duty, inrush and required rating or setting.
- Fault duty: available fault current, upstream device and coordination requirement.
- Protection: poles, B/C/D or trip-unit settings, residual-current or other special function.
- Integration: panel make/model, mounting, bus, terminals, dimensions and accessories.
- Order evidence: full existing model, photo, one-line diagram, quantity, destination and required documents.
Continue the decision
Use the next page for the next selection question
These verified SENTOP pages cover the product families and comparisons most closely connected to breaker sizing.
Frequently asked questions
Circuit breaker size questions, answered clearly
What are the most common circuit breaker sizes?
In many U.S. building panels, 15 A and 20 A are common branch ratings, while 30 A, 40 A, 50 A and 60 A are often used for equipment or larger circuits. The current NEC standard series also includes 10, 25, 35, 45, 70, 80, 90, 100, 110, 125 A and many larger values through 6,000 A. Availability and suitability depend on the exact breaker family and application.
Are circuit breaker sizes standardized worldwide?
No. Standards define product scopes, tests and ratings, but U.S. panel breakers, IEC/DIN MCBs, MCCBs and power breakers use different physical formats, voltage systems, trip technologies and approvals. Always check the applicable standard, manufacturer drawing and panel or enclosure compatibility.
What does a 100 A frame circuit breaker mean?
Frame size normally identifies the largest ampere rating available in a group of similar breaker construction. It is not always the actual continuous-current or long-time trip setting. Applicable electronic-trip breakers may also use a sensor, rating plug and adjustable setting. Read the complete label and trip-unit documentation.
Are all 20 A breakers physically the same size?
No. A 20 A device can be a plug-in panel breaker, bolt-on breaker, DIN-rail MCB, compact MCCB or supplementary protector. Width, depth, bus connection, pole count, terminals and approved panel use vary. Match the complete model and panel label, not just 20 A.
Can I replace a 15 A breaker with a 20 A breaker?
Not as a simple upgrade. The conductor, terminals, circuit load, panelboard and applicable electrical rules must support the 20 A overcurrent device. Increasing the breaker to stop trips can leave a conductor underprotected or conceal a fault. Have the circuit evaluated by a qualified professional.
What do B, C and D mean on an MCB?
They are commonly used IEC/EN 60898-1 instantaneous-trip characteristic categories: B is 3–5 times rated current, C is 5–10 times and D is 10–20 times. They are not physical sizes or quality grades. Selection must consider load inrush, conductor protection, available fault current and required disconnection time.
Does a higher kA rating mean I can use a larger breaker?
No. The kA or interrupting rating describes fault interruption under stated conditions. It does not set conductor ampacity, normal load current, pole count, trip curve or panel compatibility. It is one required selection field alongside the ampere rating.
Can I use any breaker that fits my panel?
No. Physical fit does not prove approved bus engagement or panelboard suitability. Follow the panelboard marking and manufacturer documentation. Only use a classified replacement where the exact breaker and panel combination is specifically covered.
Technical references
Check the source that applies to the system and market
These sources support the rating, scope and compatibility framework. The locally adopted code, exact product data and qualified project review take priority for installation.
IEC 60898-1:2015 — AC household and similar MCB scope, including 125 A and 440 V limits.
IEC 60947-2:2024 — Industrial circuit-breaker scope up to 1,000 V AC or 1,500 V DC.
Eaton 2023 NEC code update — Table 240.6(A) standard ampere series and addition of 10 A.
UL Panelboard Application Guide — Frame-size definition and panelboard compatibility.
UL Circuit Breaker Services — UL 489 breaker and UL 1077 supplementary-protector distinction.
Schneider Electric — Frame, sensor, sensor plug and rating-plug explanation.
Schneider Electric — Minimum MCB selection data: poles, curve, amps, breaking capacity and voltage.
Siemens SENTRON primer — B, C and D instantaneous-trip ranges and MCB behavior.
Need model or project support?
Send the complete breaker requirement for review
Include the circuit function, system voltage, current, poles, load and inrush, conductor, available fault current, panel model, mounting, required standard, quantity and full replacement reference.
