NEC 250.119 + 310.120 — why the equipment ground is green (or green with yellow stripes), and the five markings every conductor must carry

250.119 (Identification of Equipment Grounding Conductors) and 310.120 (Marking) verbatim — the green / green-striped rule, its three exceptions, the 4 AWG-and-larger identification requirement, and the five required 310.120 markings with their 24-in / 40-in repeat intervals — plus Table 250.122 minimum EGC sizes and the 250.122(B) proportional-increase rule, and seven worked examples where every number is computed by the shipped calculator core. Last updated 2026-09-01 (written for PanelWright v1.16).

Runs in your browser. No account, no install, data never leaves your machine. The panel card sizes every branch circuit against its load and applies the 310.15 corrections and 240.4(D) small-conductor caps as the governing ampacity — and the Conductor derating + voltage-drop cards use the very Table 8, Chapter 9 resistance data the 310.120 marking rule points you to (the exact pipeline this article explains).

The rule in one sentence

Two sections, two jobs. 250.119 says the equipment grounding conductor (the green wire, the bare ground, the equipment-bond path) may be bare, covered, or insulated — but if it is covered or insulated its outer finish must be green, or green with one or more yellow stripes, and a green (or green-striped) conductor may never be used as a circuit or neutral conductor (three narrow exceptions aside). 310.120 says every conductor and cable must be marked with five things — the maximum rated voltage, the type letter(s), the manufacturer's identifying mark, the AWG size or circular-mil area, and (where the neutral is undersized) a note to that effect — with the size repeated at least every 24 in. and the other markings at least every 40 in. (or, for most metal-covered multiconductor cables, a continuous internal marker tape). Size the EGC itself with Table 250.122 and the 250.122(B) proportional rule.

The code text (verbatim, with edition notes)

250.119 — Identification of Equipment Grounding Conductors (lead-in + exceptions, verbatim)

Three ideas carry the section. (1) The EGC is the one conductor that may be bare — no other premises-wire is permitted bare in a raceway. (2) If it is covered or insulated, its finish is green or green with one or more yellow stripes. (3) The color is a one-way ticket: a green or green-striped conductor shall not be used for ungrounded or grounded circuit conductors. That last sentence is why you never "re-purpose" a spare green as a hot or neutral — the code has reserved it.

250.119(A) — Conductors 4 AWG and Larger (verbatim)

This is the branch that matters for feeders, services, and large EGCs: once the ground reaches 4 AWG copper or larger, the "green finish" is no longer enough on its own — it must be permanently identified at each end and every accessible point, by one of the three listed means, and the ID must encircle the conductor. Note the asymmetry with the small sizes: a 12 AWG green EGC needs no end-tag at all; a 4/0 copper ground does.

310.120 — Marking (verbatim)

Read 310.120 as two parts. (A) is the what: five required markings, and the fourth one — "the AWG size or circular mil area" — is the one that ties straight into the resistance math. (B) is the how and how often: surface marking for the listed single/multiconductor and cable types, with the size repeated every 24 in. and everything else every 40 in.; internal marker tape for most metal-covered multiconductor cables; and coil/reel/carton tags for Type MI, switchboard wire, and single-conductor metal-covered cable. The Informational Note is doing real work — it tells you where to look up the circular-mil area that (A)(4) requires you to print.

Table 250.122 — Minimum Size Equipment Grounding Conductors (verbatim, low rows)

The table is a minimum, keyed to the rating of the overcurrent device ahead — not to the load and not to the wire. And two rules from the 250.122 text govern its use: (A) the EGC is never required to be larger than the circuit conductors it protects, and (B) if you increase the ungrounded conductors from the minimum-ampacity size, the wire-type EGC increases proportionately by circular-mil area. Both are worked below.

Worked examples (all computed by the shipped core under node)

Every number below is produced by the shipped cores in app.js (CH9_T8 / ch9Row() for Table 8 circular-mil areas, pickConductor31016(), voltageDrop(), smallConductorCap()) running under node this session — see income-lab/compute_art20.js → calc_250119_cited.json — and is asserted in the public test suite (test/run_tests.js in the public repo). The two sections and the table are code text (quoted verbatim above); the determinations and the conductor/resistance picks are computed from that text + the shipped cores, not hand-asserted.

EX1 — the green rule, decision table (250.119 lead-in)

Derived directly from the 250.119 lead-in: the EGC may be bare, green, or green-striped; but green/green-striped is not usable as a circuit or neutral conductor outside the three named exceptions. The "green as hot" row is the violation the section exists to prevent — the one-way reservation in the last sentence of the lead-in.

EX2 — Table 250.122 minimum EGC for common circuits (computed)

Computed by the shipped core from the verbatim Table 250.122. The row that teaches the concept is the 60 A case: the minimum EGC (8 AWG) is smaller than the circuit conductor (4 AWG) — the table sets a floor, not a match, and 250.122(A) only caps it so the EGC is never required larger than the circuit. The 100 A row flags the 250.122(B) boundary: a voltage-drop upsizing does not force the EGC up; only an ampacity-driven upsizing does (EX4).

EX3 — 250.119(A): identifying a 4 AWG-and-larger EGC (determination)

Determined from the verbatim 250.119(A). This is the rule that turns a big green feeder ground into a code-compliant one: at each accessible point the ground must be identifiable as the ground, by one of the three means, wrapping the full circumference. It is the same green-identification idea as the small-size lead-in, elevated to "each end + every accessible point" because a 4 AWG+ ground is no longer visually distinguishable from a big copper circuit conductor by finish alone.

EX4 — 250.122(B) proportional increase (computed from Table 8 circular-mil areas)

Computed by the shipped core from CH9_T8 circular-mil areas. This is the 250.122(B) rule doing its job: the 200 A circuit's table EGC is 4 AWG (41,740 cmil), but the ungrounded conductors were upsized from the minimum-ampacity 3/0 to 4/0, so the EGC scales up proportionately to 52,635 cmil. The example is almost too clean for a code trap: 3 AWG (52,620 cmil) falls 15 circular mils short — so the proportional EGC lands on 2 AWG, not 3 AWG. The (B) trigger is specifically an ampacity-driven upsizing from the minimum-ampacity size; a voltage-drop upsizing (EX2, 100 A row) does not run this rule.

EX5 — the "not larger than the circuit" cap (250.122(A))

250.122(A) is a one-sided rule: the EGC shall not be required to be larger than the circuit conductors. It does not forbid a larger EGC — it just removes the requirement. In practice the table minimum is almost always at or below the circuit size for the low rows (12-on-12, 10-on-10, 8-on-4, 6-on-1/0), so the cap rarely binds below the 200 A row.

EX6 — 310.120(B)(1) marker repeat intervals (computed counts)

Computed by the shipped core from the two 310.120(B)(1) intervals: 100 ft = 1,200 in.; 1,200 / 24 = 50 size marks per 100 ft (ceiling), 1,200 / 40 = 30 other-marking positions per 100 ft. This is the "how often" that makes the "what" of (A) physically realizable — you cannot comply with "repeat the size every 24 in." without the size actually being printed along the conductor, and that is what the (A)(4) Informational Note (Table 8, Chapter 9) supports by telling you where the circular-mil value comes from.

EX7 — resistance sense of an EGC (computed from Table 8, Chapter 9)

Sense-check only — the EGC is sized by Table 250.122 / 250.122(B), not for voltage drop. Its job is to provide a low-impedance fault path so the overcurrent device clears. This example just shows the ohms-per-kft the core uses (Table 8, Chapter 9 — the same table the 310.120(A)(4) Informational Note points to) so a reader can see why a 10 AWG EGC on a 30 A branch is a real, low-resistance path. The 30 A current is illustrative, not the circuit load.

Editions: 2014 / 2017 / 2020 / 2023 — and the Article 310 renumber

• 250.119 (Article 250) — stable number and color rule. 250.119 kept its number through 2017 and 2020 (Article 250 was not renumbered), and the green / green-with-yellow-stripes rule plus the "shall not be used for ungrounded or grounded circuit conductors" reservation is the operative text quoted above. This article cites the verbatim 2017 official NFPA text on disk; the 2023 body is account-gated, so the 2017 text is the citation anchor and the values are flagged "verify against the adopted edition."
• 310.120 → 310.8 (2020 renumber) — the one that moves. In the 2020 edition Article 310 was renumbered and 310.120 "Marking" became 310.8. This is confirmed on disk: the 2020 edition's 210.5(C)(2) text (polarity marking) cites the repeat-interval rule as "in accordance with 310.8(B)" where the 2017 numbering read "310.120(B)." The substance — the five required markings, the 24-in size / 40-in other repeat intervals, the internal marker tape — is the marking rule, just renumbered. up.codes lists the section by the title "Marking." If you are working in a 2020+ jurisdiction, the same rule you are reading here is cited as 310.8.
• 2023 — gated, no change claimed. The 2023 full text for both sections is account-gated (up.codes 2023 viewer; ELR login-walled), so this article does not assert a 2023 word-diff or a "no 2023 change" from a gated source. The 2017 official text is the quote anchor; verify 2020 (310.8 renumber) and 2023 wording against the adopted edition.
• Honest sourcing note. The on-disk 2020 full-code scan ends at Article 230, so the 250.119 / 310.120 bodies are not on disk for a 2020 word-level diff — only the 310.120→310.8 renumber (via the 210.5(C)(2) cross-reference) is. This article says so rather than over-claiming a diff it did not run.

Free panel schedule & service-load tools

The panel card sizes every branch circuit against its load and checks the 210.11(C) dwelling-circuit mandates — the very circuits whose equipment grounds this article sizes. The Conductor derating card applies the 310.15(B)(1) + 310.15(C)(1) corrections and the 240.4(D) small-conductor caps as the governing ampacity, and the voltage-drop card uses the Table 8, Chapter 9 resistance data that 310.120(A)(4)'s Informational Note points you to (the exact EX7 pipeline). Breaker picks use the NEC 240.6(A) standard-size list. All results print in the rollup CSV export and the branded PDF project report.

Sources & verification