Which NEC article governs overcurrent protection devices and their rating?

• A. Article 250
• B. Article 240
• C. Article 300
• D. Article 310

Answer: (B)

Overcurrent protection devices—like fuses and circuit breakers—and their ratings are governed by NEC Article 240. This article specifies how these devices are sized and selected to protect conductors from overheating and to interrupt fault currents safely. The key idea is that the device’s ampere rating is chosen based on the conductor’s ampacity and the load, so the protection limits are matched to what the wiring can safely carry. It also covers the interrupting rating, which is the maximum fault current the device can safely interrupt.

To bring it to life, think of a branch circuit with conductors rated for a certain ampacity; the overcurrent device on that circuit must have a rating that does not exceed that conductor ampacity (with exceptions for continuous loads and other considerations). This ensures the wiring isn’t exposed to excessive current that could cause overheating or damage. Other NEC articles cover different topics: grounding and bonding in Article 250, general wiring methods in Article 300, and conductors themselves in Article 310. Those areas are related to wiring safety but do not govern how overcurrent protection devices are sized and rated.