⚡ NEC 2023 · Art. 210.20

Breaker Sizing Calculator — NEC 2023

Size circuit breakers and fuses for continuous and non-continuous loads per NEC 210.20(A). Get the next standard OCPD size instantly.

✓ Continuous load 125% rule✓ Standard breaker sizes✓ NEC 240.4(D) hard block limits

OCPD Sizing Inputs

NEC 2023 Art. 210.20(A) — OCPD rating for branch circuits

Load Type

Continuous Load Current (A)

Non-Continuous Load Current (A)

Conductor Size (for NEC 240.4(D) check)

OCPD Type

Breaker Size Result

Enter load values and click Size Breaker

Enter your load current above to calculate the required OCPD rating per NEC 210.20(A).

NEC 210.20 Full Compliance Analysis🔒 Pro

NEC 210.20(A): OCPD rating ≥ 125% of continuous load plus 100% of non-continuous...
NEC 240.4(D): 14 AWG = 15A max, 12 AWG = 20A max, 10 AWG = 30A max...
Exception: Assembly-listed equipment rated 100% duty at 100%...

NEC breaker sizing rules explained

NEC 210.20(A) — Continuous loads

Any load that operates for 3 or more hours continuously is a "continuous load." The OCPD must be rated at 125% of the continuous load current, plus 100% of any non-continuous load on the same circuit.

NEC 240.4(D) — Small conductor protection

Hard limits regardless of load: 14 AWG = 15A max, 12 AWG = 20A max, 10 AWG = 30A max. These override other sizing rules.

Standard OCPD sizes (NEC 240.6(A))

Standard Sizes (A)	Common Uses
15, 20, 25	Residential branch circuits
30, 35, 40	Appliances, A/C, dryers
45, 50, 60	Range circuits, sub-panels
70, 80, 90, 100	Sub-panels, service entrance
110–1200	Feeders, services

Frequently asked questions

What is the 125% rule for continuous loads? ▾

NEC 210.20(A) requires that the OCPD rating be at least 125% of the continuous load. This accounts for the heat generated when a breaker carries 100% of its rating for 3+ hours continuously — most standard breakers are only rated for 80% continuous duty at their listed amperage. For example, a 16A continuous load requires a minimum 20A breaker (16 × 1.25 = 20A).

Can I use a 100% rated breaker for continuous loads? ▾

Yes. NEC 210.20(A) includes an exception: where both the assembly and OCPD are listed and identified for operation at 100% of their rating, the 125% rule does not apply. Square D QO and some industrial-grade breakers are 100% rated. The breaker AND the panelboard must both be rated for 100% continuous use.

How do I size a breaker for a motor circuit? ▾

Motor branch circuit protection is governed by NEC 430.52, not 210.20. Motor OCP is sized based on motor FLA and the type of protective device — typically 250% for inverse time breakers. Use the Motor Protection Calculator for motor circuits.

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