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Episode 3 — Big OCPDs and the Small Conductor Table
Episode 3 — Big OCPDs and the Small Conductor Table
Covers: 240.4(C), 240.4(D)
Hook: Now flip it — what happens once your OCPD is rated over 800A? And what about the tiny stuff, like 18 AWG control wire?
Slide 2: Once the OCPD is rated over 800A, the round-up rule disappears — the conductor's ampacity has to be equal to or greater than the actual OCPD rating, full stop.
Slide 3: Small conductors get their own fixed maximum protection, correction factors applied first: 18 AWG copper caps at 7A (if continuous load ≤5.6A and protected by specific fuse classes or marked OCPDs), 16 AWG copper at 10A, 14 AWG copper-clad aluminum at 10A (same conditions), 14 AWG copper at 15A, 12 AWG aluminum/copper-clad at 15A, 12 AWG copper at 20A, 10 AWG aluminum/copper-clad at 25A, and 10 AWG copper at 30A.
Quiz: What's the max standard overcurrent protection for 12 AWG copper under 240.4(D)?
Answer: 20 amperes.
CTA: Follow — tap conductors and transformer secondaries are next.
⚠️ Educational NoticeQuick Hits are educational explanations based on my understanding of the NEC. Always verify requirements in the current adopted NEC, applicable local amendments, manufacturer instructions, and with the AHJ.
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