NEC 402 — Fixture Wires (2017 vs 2023)

The wire inside every luminaire: fixture wires — the short, code-limited runs that connect a luminaire to its branch-circuit conductors. Below: all 11 on-disk 2017 sections verbatim from the NFPA scan, all 12 on-disk 2023 rows (10 top-level + 2 sub-rows of 402.9), the Table 402.5 ampacity table (byte-identical across editions), Table 402.3 (31 fixture-wire types on disk), 4 machine-diffed 2017→2023 deltas — including the real 2023 change, which sits in the companion 240.5(B)(2) — and six core-computed worked examples (zero hand math). One more honest find: Article 403 is a numbering gap — it exists in neither edition.

402.1 — Scope (unchanged)

402.2 — Other Articles (the Part VI precision delta)

402.3 — Types (the Table 402.3 fixture-wire-type table)

The on-disk 2023 table carries 31 fixture-wire types — from 60 °C thermoplastic (TF*/TFF*) up to 250 °C nickel-based perfluoro-alkoxy / extruded PTFE (PAF/PTF). Machine-parsed letter → max operating temperature (all 31 asserted in the verify script):

402.5 — Ampacity (the "allowable" reword + the 310 re-cite)

Table 402.5 — Allowable Ampacity for Fixture Wires (byte-identical)

402.6 — Minimum Size · 402.7 — Fill · 402.8 — Grounded Conductor ID (unchanged)

402.9 — Marking (word-identical modulo the (A)/(B) sub-headings)

402.10 — Uses Permitted · 402.12 — Uses Not Permitted (unchanged)

402.14 — Overcurrent Protection (unchanged; the companion rule is the real 2023 delta)

The identity set (machine-verified, alnum-normalized, zero OCR repair)

Count: 9 rows identical (402.1, 402.3-prose, 402.6, 402.7, 402.8, 402.9-modulo-headings, 402.10, 402.12, 402.14 — with 402.3 counting its prose as identical and its grid flagged), 2 sections carrying deltas (402.2, 402.5), plus the companion 240.5(B)(2) delta (D4). Every verdict above was produced by the machine diff in s97_identity.py (both sides on disk, alnum-normalized) and re-asserted by verify_art72.py.

The 403 question — Article 403 is a numbering gap (verified both editions)

Prior planning notes in this series kept carrying "NEC 402-403" as a candidate. Verified against disk this session: the 2023 on-disk dataset has zero Article-403 rows (machine-counted, 0) and the 2017 on-disk scan has zero 403.x tokens (machine-counted, 0 hits). Article 403 is a numbering gap in the NEC — the 400-family runs 400 (Flexible Cords & Flexible Cables), 402 (Fixture Wires), 404 (Switches), 406 (Receptacles), 408 (Switchboards/Switchgear/Panelboards) with no 403 in either edition on disk. This article therefore covers 402 as a complete single-article story; there is no 403 text to cover, and none is asserted.

Worked examples (core-computed, zero hand math)

EX1 — 18 AWG fixture wire: the 2023 15 A tap row

On-disk Table 402.5: 18 AWG = 6 A. 240.5(B)(2) row 1 (2023 on disk): "15- or 20-ampere circuits — 18 AWG, up to 15 m (50 ft)". Under 240.5(A) (ampacity-based protection) the OCPD must not exceed the 6 A ampacity: shipped core nextStdBreaker(6) = 15 A — the smallest standard rating at/above 6 A, and the same device the branch tap itself runs under. The 15 A branch is legal in 2023; in 2017 the row said "20-ampere circuits" only. (D4 in action.)

on-disk 18 AWG = 6 A; core nextStdBreaker(6) = 15 A; 2023 row: "15- or 20-ampere circuits, up to 15 m (50 ft)"

EX2 — 16 AWG: the 100 ft 15 A tap (legal only because of 2023)

On-disk Table 402.5: 16 AWG = 8 A; core nextStdBreaker(8) = 15 A. 240.5(B)(2) row 2 (2023 on disk): "15- or 20-ampere circuits — 16 AWG, up to 30 m (100 ft)". A 100 ft 16 AWG fixture-wire tap on a 15 A circuit is permitted by the 2023 row; the 2017 row ("20-ampere circuits") did not state 15 A.

on-disk 16 AWG = 8 A; core nextStdBreaker(8) = 15 A; 2023 row: "15- or 20-ampere circuits, up to 30 m (100 ft)"

EX3 — 14 AWG: the unchanged 20 A row

On-disk Table 402.5: 14 AWG = 17 A; core nextStdBreaker(17) = 20 A. 240.5(B)(2) row 3 is "20-ampere circuits — 14 AWG and larger" in BOTH editions (machine-identical) — the 2023 delta stops at rows 1–2. A 14 AWG fixture wire on a 30 A circuit (row 4, also identical) is likewise unchanged.

on-disk 14 AWG = 17 A; core nextStdBreaker(17) = 20 A; row 3 identical both editions

EX4 — 12 AWG: the 40/50 A tap rows

On-disk Table 402.5: 12 AWG = 23 A; core nextStdBreaker(23) = 25 A. 240.5(B)(2) rows 5–6 (both editions, machine-identical): 40 A and 50 A circuits — 12 AWG and larger.

on-disk 12 AWG = 23 A; core nextStdBreaker(23) = 25 A; rows 5-6 identical both editions

EX5 — 10 AWG: the 240.5(A) ampacity path

On-disk Table 402.5: 10 AWG = 28 A (the table's bottom row). Fixture wire is not a tap size in 240.5(B)(2) — its protection goes through 240.5(A) (OCPD per ampacity): core nextStdBreaker(28) = 30 A, the smallest standard rating at/above the 28 A ampacity.

on-disk 10 AWG = 28 A; core nextStdBreaker(28) = 30 A (240.5(A) path)

EX6 — the Table 402.3 temperature span (on-disk values)

The on-disk 2023 Table 402.3 spans 60 °C (140 °F) (TF*/TFF* thermoplastic) to 250 °C (482 °F) (PAF/PTF, nickel or nickel-coated copper). Machine ratio: 250 ÷ 60 = 4.17× — the 402.5 operating-temperature cap ranges across that span by insulation type, which is exactly why 402.5 re-cites the 310.14(A)(3) temperature-limitation rule rather than restating it.

on-disk 60 °C (TF/TFF) … 250 °C (PAF/PTF); core round2(250/60) = 4.17

Frequently asked questions

Sources & verification method

• 2017 text: on-disk official NFPA 70 (2017 NEC) scan, Article 402 region (ARTICLE 402 heading at line 44095, ending before the ARTICLE 404 heading at 44875; the 2017 scan's Article 402 is 402.1-402.14 — 11 top-level sections, the Table 402.3 grid printed on two interleaved pages, and the Table 402.5 grid printed on the 402.14 page), machine-reflowed + dehyphenated into s97_402_2017_sections.json. Disclosed scan artifacts (each machine-asserted in the verify script): the Table 402.3 grid is layout-interleaved across the page break with OCR artifacts ("150°G" for 150 °C in the PGFF row; "(392°)" missing °F in the ZHF row; "XFE*" printed where the 2023 dataset has "XFF*" — flagged, not asserted as a code change); the trailing comma in 402.6 ("18 AWG,") is kept as-printed; the 400.36 tail (Article 400 Part III bleed) before the ARTICLE 402 heading was dropped as out-of-region; the page furniture ("70-251"…"70-254", running headers) stripped. The 240.5(B)(2) quote is from the on-disk scan §240.5 (reflowed; the scan numbers its six rows (1)-(6)).
• 2023 text: on-disk 2023 NEC dataset (art35_nec_csv.csv), all 12 Article-402 rows (10 top-level 402.1-402.14 + sub-rows 402.9(A)/(B)) — the complete article in the dataset. Disclosed dataset artifacts: the list-item concatenation in 240.5(B)(2) (the six tap rows print run-together) and the antflix per-section citation links (stripped for clean quoting). Table 402.3 (31 type rows) and Table 402.5 (5 rows) reproduced verbatim from the on-disk rows.
• Mike Holt 2023 change summary: on-disk (art48_mh23cc_full.txt) — zero in-scope Article 402 entries (machine-counted silence: no 402.x tokens in the file). All four deltas are direct on-disk diffs, not summary claims.
• 2020 edition gap: the on-disk 2020 source (slideshare scan) carries no Article 402 body — its article range is 90-230 (headings 100, 110, 200, 210, 215, 220, 225, 230) and its only Article-402 token is a single cross-reference, "402.8", inside Article 200's grounded-conductor-identification list ((7) "Fixture wire shall comply with the requirements for grounded conductor identification as specified in 402.8") — no Article 402 section body, machine-asserted. So the edition story is 2017 ↔ 2023, both sides on disk, and no 2020 position is claimed.
• Worked examples: every number computed by the shipped PanelWright core (nextStdBreaker, round2) under node (compute_art72.js → art72_numbers.json) or quoted from on-disk rule values (Table 402.5 ampacities, Table 402.3 temperatures, the 240.5(B)(2) tap rows) — zero hand math; the test suite re-runs the core and compares against the JSON.
• Verification: verify_art72.py runs the machine checks (all 12 2023 rows present via the CSV state machine, all 11 2017 sections referenced, the 4 deltas both-sided, the 9-row identity set incl. 402.9-modulo-headings, the Table 402.5 5-row byte-identity, the 31 Table 402.3 type letters, the 2020-gap + MH-silence + 403-gap absence proofs, the OCR-artifact disclosures, the 6 worked-figure probes, the core re-run, the sitemap/index/README entries, tag balance, footer self-consistency) — the count in the footer is the script's actual total, and a self-consistency check prevents the page from claiming a number the verifier does not run. 157 machine-verified checks — all 157 pass.

Scope & honesty: this is a design aid, not code commentary and not engineering advice. The adopted edition in your jurisdiction governs. Where 2017 and 2023 differ, the delta boxes say what moved; where a number is quoted from a scan, the disclosed artifacts are listed. AI-built, AI-verified, fully disclosed.