NEC ReferenceNEC 2023 · 2026 · Updated Apr 2026

NEC Article 240: Overcurrent Protection & Breaker Sizes

NEC Article 240: Overcurrent Protection covers standard sizes through vs circuit breakers. This guide explains each major section with practical interpretation for electricians.

240.6(A) Standard Sizes

Standard overcurrent device ratings: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600. You cannot use non-standard sizes - a wire rated 55A still uses a 50A breaker.

240.4(B) Next Size Up Rule

If the ampacity of a conductor does not match a standard overcurrent device rating, the next higher standard rating is permitted - but ONLY for circuits 800A or less, and only if the overcurrent device is not part of a multioutlet branch circuit. Example: 8 AWG THHN is rated 50A - it can be protected by a 50A breaker.

240.4(D) Small Conductor Protection

14 AWG must not be protected above 15A. 12 AWG must not be protected above 20A. 10 AWG must not be protected above 30A. These limits are absolute - the next-size-up rule does not override them.

240.21 Tap Rules

A tap is a conductor connected to a circuit but not protected at its full ampacity. The 10-foot tap rule (240.21(B)(1)): conductor can be unprotected for up to 10 feet if it has ampacity not less than the rating of the device at the tap end. The 25-foot tap rule adds additional conditions.

Fuses vs Circuit Breakers

Both provide overcurrent protection. Fuses are typically faster-acting and more precise. Breakers are reusable and provide a switch function. In residential, breakers dominate. In industrial and high-fault-current applications, fuses may be required for their higher interrupting ratings.

Key NEC Tables Referenced

240.6(A) - Standard sizes

Frequently Asked Questions

What does NEC Article 240 cover?

Article 240 covers overcurrent protection requirements. Key sections include 240.6(A) Standard Sizes and 240.4(B) Next Size Up Rule. It applies to all electrical installations in the United States.

Where can I find the full text of Article 240?

The full NEC is published by NFPA and available at nfpa.org. Many libraries provide free access. Your local building department also has copies available for reference during permit applications.

Does Article 240 apply to existing wiring?

The NEC applies to new installations, modifications, and additions. Existing wiring that was code-compliant when installed is generally grandfathered unless a renovation triggers an upgrade requirement. Check with your local AHJ (authority having jurisdiction).

When did the current Article 240 requirements take effect?

NEC 2023 is the current edition. Adoption varies by state. Check your state adoption status on our state code pages.

Requirements vary by state. NEC edition, licensing, permits, and GFCI rules differ by jurisdiction. Check your state or pick it below for personalized info across WireRef.

This guide provides practical interpretation of NEC requirements. Always verify with your local AHJ and the current NEC edition adopted in your jurisdiction. WireRef is a reference tool and does not replace licensed professional judgment.

NEC 2023 references verified April 2026