Research — Illustrative (draft, unvalidated)
Breaker vs conductor — auto
No controls here. The breaker steps up through the standard ratings on 14, 12 and then 10 AWG copper at 75 °C terminals. Each time, the verdict flips at the NEC 240.4(D) small-conductor cap, not at the larger Table 310.16 ampacity, and the 240.4(B) next-size-up allowance cannot lift it.
Breaker rating
15 A240.4(D) cap (moves per conductor)40 A
Reading —
Panel, conductor cross-section and the amps bar
Breaker vs conductor
Breaker
Maximum permitted
Margin
How the check read it
Client-side port:the logic and table in this page are a TypeScript port of the harness function, checked against values exported from the Python tests. Not a live API call. Module maturity, quoted from the domain page: “Draft, unvalidated. No licensed electrician, electrical PE or inspector has reviewed any of the 13 functions, and output should not be represented as authoritative NEC guidance until a review is logged. Some table values rest on secondary sources rather than a licensed NFPA 70 copy.” The numbers on this page are a TypeScript port of the harness table, checked against values exported from the harness's own function; the sequence is staged. The conductor cross-section is a relative-size schematic from the AWG / circular-mil definitions, not harness data.Real function this maps to:
check_breaker_conductor_ampacity_match.Not modeled: the other 12 of the 13 ubm checks (this page covers only the breaker-versus-conductor match), any load calculation (no Article 220), ambient-temperature and bundling adjustment, 240.4(D)'s own exceptions, and aluminum or other temperature columns (this walkthrough fixes copper at 75 °C; the interactive page covers the rest).See also:Breaker vs conductor (interactive)