Breaker Size Chart

Use this breaker size chart after the calculator result to document the load category, conductor protection path, standard-size choice, and equipment constraints before selecting an OCPD for the panel schedule.

Open calculator

Quick reference table

Breaker sizing is an overcurrent protection worksheet, not a simple ampere conversion. Use the calculator result with calculated load and load category, then compare conductor ampacity, continuous-load treatment, equipment listing, available fault current, and standard OCPD options before verifying the adopted NEC edition and AHJ requirements.

Breaker size planning paths

Breaker size planning paths
Load category	Record first	What the calculator result must still prove
General branch circuit	Calculated non-continuous and continuous load portions	Breaker rating coordinates with conductor ampacity and terminal limits
Continuous equipment load	Load current and expected operating duration	Planning current and conductor size are both documented
Motor load	Table FLC, nameplate FLA, starting method, and overload device	Branch-circuit protection is not confused with overload protection
Transformer load	Primary and secondary current, kVA, impedance, and inrush	Equipment-specific primary and secondary protection are reviewed
EV charging load	EVSE current setting, circuit rating, service capacity	Long-duration load and panel/service capacity are checked together

Breaker result risk checks

Breaker result risk checks
Risk check	Why it matters	What to document
Interrupting rating	Breaker must be suitable for available fault current	Panel rating, series rating data, or study note
Conductor protection	Breaker normally protects connected conductors	Selected conductor size, terminal basis, and ampacity screen
Equipment listing	Listed equipment can require a maximum or specific OCPD	Nameplate or manual instruction used
Standard size step	Next standard size may not always be available for the project path	Reason the selected rating was permitted

Formula basis

Breaker planning screen = calculated load current adjusted for the load category, then compared with conductor protection limits and permitted standard OCPD sizes.

Calculated load current is the amperes from the load calculation, nameplate, or calculator result.
Load category identifies whether the circuit is continuous, non-continuous, motor, transformer, HVAC, EVSE, or equipment-specific.
OCPD means overcurrent protective device, such as a breaker or fuse selected under the applicable project path.

Worked examples

Continuous 32 A equipment loadThe worksheet should show the 32 A load, the planning current used for continuous operation, the conductor ampacity result, and the selected breaker rating before the circuit is released.

Motor feeder reviewA motor branch circuit may use one current value for conductor and short-circuit protection while overloads use nameplate data, so the chart keeps both decisions from being collapsed into one breaker number.

Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.

This chart is a planning reference and does not grant permission to use any specific breaker size.
Listed equipment, available fault current, conductor protection, and manufacturer instructions can control the final OCPD selection.
Motor, transformer, HVAC, EVSE, and service equipment workflows may require different calculation paths.

Code and standard notes. Planning limits that should be checked before final equipment selection.

Verify breaker selection with the adopted NEC edition, equipment labeling, manufacturer instructions, conductor protection rules, interrupting rating, local amendments, and the Authority Having Jurisdiction (AHJ).
Motor, transformer, HVAC, EVSE, and listed equipment can follow different overcurrent protection paths, so document the path used with the calculator result.

How to use this chart

1Classify the load firstRecord whether the load is continuous, non-continuous, motor, transformer, HVAC, EVSE, or equipment-specific before choosing a breaker path.

2Tie breaker to conductorUse the breaker calculator result with the wire size or ampacity result so conductor protection, terminal rating, and OCPD selection stay aligned.

3Check equipment constraintsBefore selecting the breaker, review panel compatibility, interrupting rating, listed equipment maximum OCPD, and manufacturer instructions.

Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.

Record calculated currentUse measured current, calculated load current, nameplate data, or schedule data and identify the source of that current on the worksheet.
Document the sizing pathMark the load category and note why any continuous-load factor, motor path, transformer path, or equipment-specific limit was used.
Verify before panel scheduleCompare the selected breaker with conductor ampacity, equipment labels, available fault current, and the adopted NEC path before updating the panel schedule.

Common mistakes to avoid. Review these before turning chart current into an equipment decision.

Sizing a breaker from watts or amps alone without checking load classification, conductor limits, interrupting rating, and equipment instructions.
Assuming the next larger standard breaker is always allowed without verifying the applicable path and conductor protection limits.
Using the same breaker sizing logic for motors, transformers, EVSE, HVAC, and general branch circuits even though their protection workflows can differ.

Frequently asked questions

These answers explain how to use the chart without turning a quick reference into a final design decision.

Can I size a breaker from watts alone?

No. Convert the load to current first, identify the load category, check conductor compatibility, and verify the equipment and code path before choosing a breaker.

Why is conductor compatibility part of breaker sizing?

A breaker must normally protect the connected conductors. The worksheet keeps conductor ampacity, terminal rating, and breaker selection together instead of treating the breaker as an isolated number.

Does open panel space mean a breaker can be added?

No. Open space does not prove load capacity, interrupting rating, compatibility, or equipment listing. Use the load and breaker calculators before changing the panel schedule.