Quick Hits

Episode 2 — Protecting Conductors: The Basic Rule and Rounding Up

Covers: 240.4, 240.4(A), 240.4(B)

Hook: The core rule of this whole article: conductors get protected according to their ampacity. Here's the exception everyone actually uses.

Slide 2: Conductors (other than flex cords/cables/fixture wires) need overcurrent protection matching their Table 310.14 ampacity — unless 240.4(A) through (H) says otherwise. One exception: where interrupting the circuit itself creates a hazard (fire pump circuits, material-handling magnets), overload protection isn't required, but short-circuit protection still is.

Slide 3: The "round-up" rule: for OCPDs rated 800A or less, if the conductor's ampacity doesn't match a standard breaker/fuse size, you can bump up to the next higher standard rating — but only if the conductor isn't feeding a multi-receptacle cord-and-plug branch circuit, the OCPD has no adjustable trip that exceeds its rating, and the rounded-up size doesn't exceed 800A. Example: a 380A-rated 500 kcmil conductor can be protected by a 400A device.

Quiz: What's the maximum OCPD rating the "round up to the next standard size" rule can apply to?
Answer: 800 amperes.

CTA: Follow — devices over 800A and the small-conductor table are next.

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