Input Workflow
Breaker Sizing Inputs
Load Condition
Breaker Review Scope
Field Advisory
Recommended Output
:
Entered Load
System Voltage
Base Load Current
Sizing Basis
Headroom Remaining
of
Circuit Edge Case Review
Light Conductor Hint
Workflow Position
Load → Breaker → Voltage
Decision Note
Use this as a breaker checkpoint. Final conductor selection, terminations, and equipment instructions still need review before installation.
Next Field Step
Carry this breaker result into conductor sizing
The handoff passes load amps, selected breaker size, circuit voltage, and source context into the wire sizing workflow.
Breaker Sizing Technical Reference
How this NEC breaker size calculator should be used in the field
Use this reference after entering the connected load, voltage, and load condition. The calculator screens the load-to-breaker relationship, then points the result into conductor ampacity, voltage-drop, and raceway checks before installation.
Step 1
Convert load to amps
The entered watts or VA is divided by the selected circuit voltage to estimate load current.
Step 2
Apply load basis
When continuous load is selected, the calculator applies a 125% sizing factor before breaker matching.
Step 3
Match OCPD rating
The adjusted amperage is compared to the tool’s standard breaker rating list.
Step 4
Review headroom
The result reports utilization and headroom so near-limit loads are easier to spot.
Formula basis: load amps = connected load ÷ circuit voltage. Continuous-load review uses adjusted amps = load amps × 1.25 before standard breaker matching.
A 7,200 VA load on a 240V circuit equals 30A before adjustment. If the load is continuous, the calculator multiplies 30A by 125%, giving 37.5A. The next standard breaker rating in the tool list is 40A.
Input
7,200 VA
Voltage
240V
Adjusted
37.5A
Screened OCPD
40A
NEC 210.20(A)
Used as the branch-circuit continuous-load reference for screening loads expected to run 3 hours or more.
NEC 215.3
Referenced for feeder overcurrent protection context when the review moves beyond a single branch-circuit check.
NEC 240.6(A)
Used for standard ampere rating matching after the load current and continuous-load basis are determined.
Source scope: this page screens load-to-current conversion, continuous-load adjustment, and standard breaker rating selection. It does not evaluate conductor ampacity, terminal temperature ratings, equipment nameplate limits, voltage drop, or raceway fill.
Review Breaker Size Source LogRelated Code References
NEC Continuous Load 125% Rule
Breaker sizing adjustment context
NEC 240.4(B) Next-Size-Up Rule
OCPD and conductor boundary
NEC 240.4(D) Small Conductor Rule
Small-conductor breaker limits
NEC 110.14(C) Terminal Temperature
Conductor termination limit context
NEC 310.16 Ampacity Table
Conductor ampacity chart basis
NEC 430.52 Motor OCPD
Motor protection boundary
NEC 110.3(B) Listed Equipment
Nameplate and listing instructions
Code Citation & Source Log
Source alignment for this workflow
Pass
The adjusted load fits a listed breaker size with usable headroom. Continue to conductor and installation checks.
Warning
High utilization, large 120V loads, residential handoff mode, or equipment-specific conditions may require closer review.
Needs Review
If the load exceeds the tool’s breaker list or comes from equipment with MCA/MOCP rules, do not rely on simple load ÷ voltage sizing.
A breaker result should sit between load review and field installation checks. Start with the Residential Load Calculator when the question is service or panel capacity. Use this page to screen the load-to-breaker relationship, then verify conductor and installation details.
Next
Wire Size Calculator
Select conductor size from the breaker and load basis.
Verify
Ampacity Calculator
Check conductor ampacity, terminal limits, and derating context.
Long Runs
Voltage Drop Calculator
Review voltage loss when distance and conductor size matter.
Raceway
Conduit Fill Calculator
Check raceway fill after conductor size and count are known.
- • Connected load entered as watts or VA.
- • Circuit voltage basis: 120V, 208V, or 240V.
- • Continuous-load adjustment when the user selects that condition.
- • Standard breaker/OCPD rating match and headroom indication.
- • Residential Load Calculator handoff context for service or panel review.
What does this breaker size calculator do?
It converts a connected load in watts or volt-amperes into amperage, applies the continuous-load factor when selected, and compares the adjusted amperage to standard OCPD ratings.
Does a continuous load change the breaker size?
Yes. When the load is expected to run for 3 hours or more, this calculator applies a 125% continuous-load adjustment before matching the result to a standard breaker rating.
Should I enter watts or VA?
Use VA when it is available, especially for motor, transformer, or inductive equipment. Watts and VA are often similar for simple resistive loads, but VA better represents the load used for circuit review.
Does this result approve the wire size?
No. The breaker result does not prove conductor ampacity, terminal temperature rating, derating, or insulation suitability. Verify the conductor with a wire size or ampacity review before installation.
Can this be used after a Residential Load Calculator handoff?
Yes. A residential load handoff should be treated as a service or panel review basis, not as a branch-circuit load that needs the continuous-load toggle applied again.
Why can the result still need review if a breaker rating is found?
A standard breaker match only screens the load-to-OCPD relationship. Equipment nameplates, motor rules, HVAC MCA/MOCP, conductor sizing, voltage drop, raceway fill, and AHJ requirements may still control the final installation.
- • Mixed continuous and non-continuous load groups should be separated before relying on one breaker result.
- • Motors, HVAC equipment, welders, transformers, and nameplate MCA/MOCP equipment may require equipment-specific rules or manufacturer instructions.
- • Large 120V loads should be checked against the actual voltage and phase basis before using the result.
- • A breaker result does not approve conductor size, terminal ratings, raceway fill, voltage drop, panel capacity, or AHJ acceptance.
This calculator is a field screening tool for breaker/OCPD sizing context. Before installation, verify the applicable NEC edition, local amendments, equipment labels, manufacturer instructions, conductor ampacity, terminal temperature rating, installation conditions, and AHJ requirements.