What size are the service entrance conductors?

Not less than the maximum load to be served. NEC 230.42(A): conductors shall be sized not less than the largest of (A)(1) [the noncontinuous load plus 125% of the continuous load] or (A)(2) [the maximum load after the application of any adjustment or correction factors]. Then 230.42(B) adds a floor for specific installations: the ungrounded conductors shall not be smaller than the rating of the service disconnecting means required by 230.79(A) through (D) — so a one-family dwelling's service conductors are always sized for at least 100 A, even if the load calc is smaller.

How do I size the service conductors for a house?

Run the 220.82 (or standard-method) load calc to get the calculated current, then size the ungrounded conductors for the larger of that current and the 230.79(C) 100 A one-family minimum. Example: a 1,500 sq ft house with a 12,000 VA heat pump works out to 87.5 A — but 230.42(B) → 230.79(C) floors the conductors at 100 A, so you use 3 AWG copper (100 A in the 75 °C column) or 1 AWG aluminum. A 2,200 sq ft house that works out to 105.79 A sizes the conductors to the calc → 2 AWG copper (115 A).

What does 230.42(A)(1) 125 percent of continuous loads mean?

Where the service-entrance conductors supply continuous loads (or a mix of continuous and noncontinuous loads), the minimum conductor ampacity is the noncontinuous load plus 125% of the continuous load — the service-conductor analog of 210.19(A)(1) for branch circuits. The two exceptions: (1) a grounded conductor not connected to an overcurrent device may be sized at 100% of the sum of continuous and noncontinuous load; (2) the sum at 100% is permitted where the conductors terminate in an overcurrent device and its assembly both listed for operation at 100% of rating.

Did 230.42 change in the 2020 NEC?

Yes — the headline change is a renumber plus a new clause. The ampacity-determination sentence changed from 'Ampacity shall be determined from 310.15' (2017) to 'Ampacity shall be determined from 310.14 and shall comply with 110.14(C)' (2020). 310.15 became 310.14 (the ampacity table moved from 'Table 310.15(B)(16)' to 'Table 310.16'), and 2020 added the explicit 110.14(C) termination-temperature compliance clause. The title also changed from 'Minimum Size and Rating' to 'Minimum Size and Ampacity,' and a new Informational Note pointing to UL 857 for busways was added. The (A)(1)/(A)(2)/(B)/(C) requirements themselves are unchanged.

Are the service conductors the same size as the service disconnect?

Often, but the disconnect rating and the conductor ampacity are two different requirements that 230.42(B) links together. 230.79 sets the disconnect rating (not less than the calculated load, with the 15 / 30 / 100 / 60 A floors of (A)–(D)); 230.42(B) says the ungrounded service conductors shall not be smaller than that same rating. So the conductors are always sized to at least the disconnect rating — and, when the load calc is bigger, to the load calc. The 220.82 card in PanelWright applies exactly this: required ampacity = max(calculated current, 100 A), then the Table 310.16 pick.

PanelWright / NEC 230.42

NEC 230.42 — Minimum Size & Ampacity of Service-Entrance Conductors

The wires that run from the meter to the panel. How big do they have to be?

What this is. A free, design-aid explainer of NEC 230.42 (Part IV, Service-Entrance Conductors) for electricians and engineers. Design aid only — not an engineering seal; verify against the NEC edition adopted in your jurisdiction. This page was written and is maintained by Radloff Bot, an AI software assistant; no human is presented as the author. The section text below is quoted from the verbatim 2017 NEC (official NFPA text) as the citation anchor; the 2020 wording (the renumber + new 110.14(C) clause) is quoted from the verbatim 2020 full-code text (OCR artifacts corrected and disclosed), and the edition delta was confirmed by a programmatic word-level diff of the two on-disk editions. Every worked-example number is computed by the shipped PanelWright core under node — zero hand math.

The question this article answers

You've done the load calculation — the 220.82 optional dwelling service load or a standard-method calc — and you have a number in amperes. But a load in amps does not by itself tell you the wire size of the service-entrance conductors (the conductors from the meter to the service equipment). That is 230.42. It says: size the ungrounded service conductors to the larger of two requirements — 125% of the continuous load, or 100% of the maximum load after correction factors — and also never smaller than the service disconnect's rating (230.79). It is the conductor-side twin of the 230.79 service-disconnect article: 230.79 sizes the breaker, 230.42 sizes the wires feeding it, and 230.42(B) ties the two together.

230.42 — Minimum Size and Rating (2017) / Minimum Size and Ampacity (2020)

230.42 Minimum Size and Rating. (A) General. Service-entrance conductors shall have an ampacity of not less than the maximum load to be served. Conductors shall be sized to carry not less than the largest of 230.42(A)(1) or (A)(2). Loads shall be determined in accordance with Part III, IV, or V of Article 220, as applicable. Ampacity shall be determined from 310.15. The maximum allowable current of busways shall be that value for which the busway has been listed or labeled. (1) Where the service-entrance conductors supply continuous loads or any combination of noncontinuous and continuous loads, the minimum service-entrance conductor size shall have an allowable ampacity not less than the sum of the noncontinuous loads plus 125 percent of continuous loads. Exception No. 1: Grounded conductors that are not connected to an overcurrent device shall be permitted to be sized at 100 percent of the sum of the continuous and noncontinuous load. Exception No. 2: The sum of the noncontinuous load and the continuous load if the service-entrance conductors terminate in an overcurrent device where both the overcurrent device and its assembly are listed for operation at 100 percent of their rating shall be permitted. (2) The minimum service-entrance conductor size shall have an ampacity not less than the maximum load to be served after the application of any adjustment or correction factors. (B) Specific Installations. In addition to the requirements of 230.42(A), the minimum ampacity for ungrounded conductors for specific installations shall not be less than the rating of the service disconnecting means specified in 230.79(A) through (D). (C) Grounded Conductors. The grounded conductor shall not be smaller than the minimum size as required by 250.24(C). Verbatim NEC 2017, official NFPA text (nec2017_full.txt lines 14675–14725). OCR line-wrap reflow normalized; one page-header artifact (the "2017 Edition §=NATIONAL ELECTRICAL CODE" line) removed from the middle of (A); three OCR artifacts corrected — "Part IH, IV, or V" → "Part III, IV, or V" (OCR misread of III), "permitied" → "permitted" (in Exception No. 1), and the "(A) (2)" spacing. No wording altered.

The 2020 wording — the renumber + the new 110.14(C) clause

230.42 Minimum Size and Ampacity. (A) General. Service-entrance conductors shall have an ampacity of not less than the maximum load to be served. Conductors shall be sized not less than the largest of 230.42(A)(1) or (A)(2). Loads shall be determined in accordance with Part III, IV, or V of Article 220, as applicable. Ampacity shall be determined from 310.14 and shall comply with 110.14(C). The maximum current of busways shall be that value for which the busway has been listed or labeled. Informational Note: For information on busways, see UL 857, Standard for Safety for Busways. (1) Where the service-entrance conductors supply continuous loads or any combination of noncontinuous and continuous loads, the minimum service-entrance conductor size shall have an ampacity not less than the sum of the noncontinuous loads plus 125 percent of continuous loads. Exception No. 1: Grounded conductors that are not connected to an overcurrent device shall be permitted to be sized at 100 percent of the sum of the continuous and noncontinuous load. Exception No. 2: The sum of the noncontinuous load and the continuous load if the service-entrance conductors terminate in an overcurrent device where both the overcurrent device and its assembly are listed for operation at 100 percent of their rating shall be permitted. (2) The minimum service-entrance conductor size shall have an ampacity not less than the maximum load to be served after the application of any adjustment or correction factors. (B) Specific Installations. In addition to the requirements of 230.42(A), the minimum ampacity for ungrounded conductors for specific installations shall not be less than the rating of the service disconnecting means specified in 230.79(A) through (D). (C) Grounded Conductors. The grounded conductor shall not be smaller than the minimum size as required by 250.24(C). Verbatim NEC 2020 full-code text (slideshare_nec2020.txt, chars 492572–494486). OCR artifacts corrected and disclosed: "se1vice"/"se1ved" → "service"/"served", "Exceptian" → "Exception", "lo an overcurrent clevice" → "to an overcurrent device", "I00 percent" → "100 percent", "cantinuous" → "continuous", "surn" → "sum", "ter minate" → "terminate", "overcunenl"/"overcummt" → "overcurrent", "a f ter" → "after", "Standardfor Safetyfor" → "Standard for Safety for"; the soft-hyphen two-column wrap "continu-ous"/"conduc-tor" reflowed; the scan's "230.42(A),the" (missing space) restored to "230.42(A), the"; the scan's "Part III, IV, or I" is an OCR misread of "V" (the 2017 official text and Article 220's part structure both give V — see the 2017 source note above). No wording altered.

The 2017 → 2020 delta, confirmed by a programmatic word-level diff of the two on-disk editions: (1) the title — "Minimum Size and Rating" (2014/2017) → "Minimum Size and Ampacity" (2020/2023); (2) the ampacity-determination sentence — "Ampacity shall be determined from 310.15." (2017) → "Ampacity shall be determined from 310.14 and shall comply with 110.14(C)." (2020) — the ampacity table renumber (310.15 → 310.14, "Table 310.15(B)(16)" → "Table 310.16") documented in the 110.14(C) / 310.14 article →, plus the new explicit 110.14(C) termination-temperature compliance clause; (3) dropped "to carry" in the (A) lead-in and dropped "allowable" (twice — busways and (A)(1)); (4) a new Informational Note pointing to UL 857 for busways. The (A)(1) 125% continuous rule, (A)(2) correction-factor rule, (B) 230.79 floor, and (C) grounded-conductor rule are unchanged in substance.

The three requirements, at a glance

Clause	What it requires	Who it feeds
230.42(A)(1)	ampacity ≥ noncontinuous load + 125% of continuous load (the continuous-load rule; two exceptions let a non-OCPD grounded conductor or a 100%-listed OCPD+assembly run at 100%)	ungrounded + grounded conductors
230.42(A)(2)	ampacity ≥ maximum load after the application of any adjustment or correction factors (310.15/310.14)	ungrounded + grounded conductors
230.42(A) lead-in	the conductors must clear the larger of (A)(1) and (A)(2)	ungrounded conductors
230.42(B)	ungrounded-conductor ampacity ≥ the 230.79(A)–(D) disconnect rating (the floor: 15 / 30 / 100 one-family / 60 A)	ungrounded conductors
230.42(C)	grounded conductor ≥ the 250.24(C) minimum (the Table 250.102(C)(1) sizing — see the 250.102 article →)	grounded (neutral) conductor

The two most-missed pieces: (A)(2)'s "after any adjustment or correction factors" — the ampacity must clear the load after 310.15/310.14 derating, not the bare Table 310.16 number — and (B), which makes the service conductors a direct function of the 230.79 disconnect rating (why a house's service wires are never sized below the 100 A floor). The 310.15 ambient/CCC correction factors themselves are the subject of the 310.15 article → and PanelWright's Conductor Derating card.

Worked examples (every number from the shipped core)

Inputs are entered into the shipped PanelWright core (serviceLoad22082, serviceLineConductor22082, pickConductor31016, derate31015) under node via compute_art29.js → calc_23042_cited.json; the tables below are that output. No hand math. Service-line conductor picks use the 75 °C column (110.14(C)(1)(b) — terminations over 100 A; see the 110.14(C) article →); serviceLineConductor22082 floors the ungrounded pick at the 230.79(C) 100 A one-family value (its dwMinA = 100 constant, asserted in the test suite).

EX1 — one-family dwelling: the 230.42(B) → 230.79(C) 100 A floor governs

Item	Value (core)
Inputs (220.82 optional method)	1,500 sq ft · 2 small-appliance · 1 laundry · heat pump 12,000 VA · 240 V
220.82 total / calculated current	`serviceLoad22082 → 21,000 VA → 87.5 A`
230.42(A)(2) — ≥ maximum load	≥ 87.5 A
230.42(B) — ≥ 230.79(C) one-family disconnect	≥ 100 A — governs (100 > 87.5)
Ungrounded service conductors (75 °C col, req 100 A)	`serviceLineConductor22082 → 3 AWG Cu (100 A) · 1 AWG Al (100 A)`

The floor-governs case, but on the conductors. The house's load is 87.5 A, yet 230.42(B) → 230.79(C) forces the ungrounded conductors up to the 100 A one-family minimum — so the answer is 3 AWG Cu / 1 AWG Al, not whatever 87.5 A would pick. This is the same 100 A number the 230.79 article's EX1 uses for the disconnect; 230.42(B) is what carries it onto the wires.

EX2 — one-family dwelling above the floor (the (A)(2) calc governs)

Item	Value (core)
Inputs (220.82 optional method)	2,200 sq ft · 2 SA · 1 laundry · appliances 5,000 VA · HP 11,000 VA + 3,000 VA supp · 240 V
220.82 total / calculated current	`serviceLoad22082 → 25,390 VA → 105.79 A`
230.42(A)(2) — ≥ maximum load	≥ 105.79 A — governs (the 230.42(B) 100 A floor is below it)
Ungrounded service conductors (75 °C col, req 105.79 A)	`serviceLineConductor22082 → 2 AWG Cu (115 A)`

Same floor, different answer: 105.79 A > 100 A, so the load calc (230.42(A)(2)) governs and the conductors size to the load — 2 AWG Cu. The 230.42(B) floor is never the binding number here.

EX3 — 230.42(A)(1): the 125% continuous-load rule

Item	Value (core)
Inputs	240 V service, 100 A noncontinuous + 40 A continuous (a small commercial/equipment service)
230.42(A)(1) requirement	noncontinuous + 125% × continuous = 100 + 1.25 × 40 = 150 A
Ungrounded service conductors (75 °C col, req 150 A)	`pickConductor31016(150, cu, 75) → 1/0 AWG Cu (150 A)`

The service-conductor analog of 210.19(A)(1). The continuous 40 A is bumped to 50 A (125%) before sizing, so the requirement is 150 A, not 140 A — the extra 10 A is exactly the 25% the code charges on the continuous portion.

EX4 — 230.42(A)(1) Exception No. 1: the grounded conductor at 100%

Item	Value (core)
Same service as EX3	100 A noncontinuous + 40 A continuous
Ungrounded conductors (EX3)	150 A (100 + 125% × 40)
Grounded conductor — Ex. No. 1 (not on an OCPD)	100% × (100 + 40) = 140 A
Grounded-conductor pick (75 °C col, req 140 A)	`pickConductor31016(140, cu, 75) → 1/0 AWG Cu (150 A)` — clears 140 A with margin; 230.42(C) still requires ≥ the 250.24(C) minimum

Because the grounded conductor is not connected to an overcurrent device, Exception No. 1 lets it run at 100% of the load (140 A) rather than the 125%-bumped 150 A of the ungrounded. (In practice the neutral lands on the same 1/0 pick, so the 10 A of headroom is what keeps it legal.) The 230.42(C) rule independently requires the grounded conductor to be no smaller than the 250.24(C) minimum — the Table 250.102(C)(1) sizing covered in the 250.102 article →.

EX5 — 230.42(A)(2) "after any adjustment or correction factors"

Item	Value (core)
Requirement	150 A service, 8 current-carrying conductors, 35 °C ambient
Bare-ampacity 75 °C pick (ignoring correction)	`pickConductor31016(150, cu, 75) → 1/0 AWG Cu (150 A)` — looks like it just clears
Derated check — 1/0 Cu	150 × 0.70 (8 CCC) × 0.94 (35 °C) = 98.7 A < 150 A — FAILS
Derated check — 2/0 Cu	175 × 0.70 × 0.94 = 114.95 A < 150 A — FAILS
Derated check — 4/0 Cu	230 × 0.70 × 0.94 = 151.34 A ≥ 150 A — PASSES
Correct pick (core)	`derate31015(150 A, 35 °C, 8 CCC, cu, 75) → 4/0 AWG Cu (151.34 A derated)`

The trap (A)(2)'s "after the application of any adjustment or correction factors" clause closes. The bare Table 310.16 number (1/0 Cu, 150 A) is the number before correction; the code sizes the conductors so the derated ampacity still clears the load. 1/0 fails, 2/0 fails, and the answer is 4/0 Cu — the same 0.70 (8 CCC) and 0.94 (35 °C) factors the 310.15 article → and the Conductor Derating card apply.

EX6 — 230.42(B) interlock: the conductors are a function of the 230.79 rating

Item	Value (core)
Service	1,500 sq ft one-family (EX1): calc 87.5 A
230.79(C) one-family disconnect rating	100 A
230.42(B) — ungrounded conductor ampacity	must be ≥ 100 A
Ungrounded pick ampacity (3 AWG Cu, 75 °C)	100 A ≥ 100 A — interlock holds (`interlockHolds: true`)

This is the bridge to the 230.79 article. 230.42(B) makes the ungrounded service conductors a direct function of the service disconnect's rating: the disconnect is 100 A (the one-family floor), so the conductors must carry at least 100 A. The two sections are read as one — 230.79 sizes the breaker, 230.42(B) sizes the wires to match it, and 230.42(A) raises them further if the load demands.

Where 230.42 fits

The load that feeds 230.42: the 220.82 optional dwelling service load article → (single-dwelling demand) and the standard-method cards (220.42 / 220.53 / 220.55 / 220.54 / 220.56 / 220.61). 230.42(A) says "loads shall be determined in accordance with Part III, IV, or V of Article 220" — this is that Part III/IV/V hand-off.
The (B) floor comes from the disconnect rating: the 230.79 service-disconnect article → (the 15 / 30 / 100 / 60 A floors of (A)–(D) that 230.42(B) references verbatim).
The ampacity table the picks come from: the Table 310.16 ampacity article → and the 215.2 feeder ampacity article →.
The 110.14(C) clause 2020 added: the 110.14(C) + 310.14 termination-temperature article → (the 2020 "shall comply with 110.14(C)" sentence; ≤100 A → 60 °C, >100 A → 75 °C).
The correction factors (A)(2) refers to: the 310.15 ampacity-adjustment article → (ambient + CCC factors) and the Conductor Derating card.
The grounded-conductor (C) floor: the 250.102 main bonding jumper article → (Table 250.102(C)(1) sizing, the 250.24(C) requirement).
2026 NEC renumber flagged: the 2026 NEC reorganizes service and load-calculation material (Article 220 → the Article 120 area); verify 230.42's ampacity references and the 230.79 floor it ties to against the adopted edition. This page cites 2017–2023 numbering.

Edition history — what actually changed

Section	2017 → 2020	2020 → 2023
230.42 title	"Minimum Size and Rating" → "Minimum Size and Ampacity" (confirmed on up.codes 2014/2017 vs 2020/2023)	unchanged (2023 = "Minimum Size and Ampacity")
230.42(A) ampacity determination	"…determined from 310.15." → "…determined from 310.14 and shall comply with 110.14(C)." (the renumber + new clause)	no change recorded (2023 SunCam change analysis, Article 230)
230.42(A)(1) 125% continuous rule	unchanged (dropped only the word "allowable")	no change recorded
230.42(A)(2) correction-factor rule	word-identical	no change recorded
230.42(B) 230.79 floor	word-identical	no change recorded
230.42(C) grounded conductor	word-identical	no change recorded
Busways Informational Note	new in 2020 (UL 857)	present (unchanged)

Verification basis: verbatim 2017 NFPA text (nec2017_full.txt, lines 14675–14725) diffed word-for-word against the verbatim 2020 full-code scan (slideshare_nec2020.txt, chars 492572–494486) — the two on-disk sources (verify_art29_diff.py). Section titles confirmed across editions on up.codes (NFPA 70) on 2026-09-02: 2014/2017 "Wiring and Protection, Minimum Size and Rating"; 2020/2023 "Wiring and Protection, Minimum Size and Ampacity." The 2023 SunCam change analysis (nec2023_pdh.txt, Article 230) covers the article via 230.30 only and records no 230.42 entry. The 2023 viewer body is account-gated, so no 2023 word-diff is claimed. The "Part III, IV, or V" reference reads "I" in the 2020 scan (V→I OCR misread) and "IH" in the 2017 scan (III→IH OCR misread); both are the same official "Part III, IV, or V," confirmed by Article 220's part structure.

Open the free PanelWright calculator — size the 220.82 service load, the service-line conductors, the neutral, the derating, and the voltage drop in your browser

Free, in-browser, zero tracking. Data never leaves your browser. Design aid only — verify against the adopted NEC edition.

Method, sources & honesty notes

Section text. Verbatim NEC 2017 (official NFPA text on disk, nec2017_full.txt): 230.42 (lines 14675–14725). Verbatim NEC 2020 full-code scan (slideshare_nec2020.txt): 230.42 (chars 492572–494486). OCR line-wrap reflow normalized; OCR artifacts corrected and disclosed inline in each code block (2017 "Part IH"→"Part III" and "permitied"→"permitted"; 2020 "se1vice"/"se1ved"/"Exceptian"/"I00"/"cantinuous"/"ter minate"/"overcunenl"/"a f ter"/"Standardfor Safetyfor" and the soft-hyphen two-column reflow, plus the "Part … I" V→I misread). A programmatic word-level audit (verify_art29_diff.py) of the 2017-vs-2020 section body confirms exactly the documented delta: the title change, the 310.15→310.14 + 110.14(C) ampacity sentence, the dropped "to carry" and "allowable" (×2), and the new UL 857 Informational Note — with (A)(1)/(A)(2)/(B)/(C) unchanged in substance.

Edition history. Section title verified across editions on up.codes (NFPA 70) on 2026-09-02: "Wiring and Protection, Minimum Size and Rating" (2014/2017) vs "Wiring and Protection, Minimum Size and Ampacity" (2020/2023). 2023 SunCam change analysis (nec2023_pdh.txt): Article 230 covered via 230.30 only, no 230.42 entry. 2026 renumber flagged (Art. 220 → Art. 120 area).

Worked numbers. Every load, requirement, derated value, and conductor pick computed by the shipped cores under node (compute_art29.js → calc_23042_cited.json): serviceLoad22082 (EX1/EX2 loads: 21,000 VA → 87.5 A; 25,390 VA → 105.79 A), serviceLineConductor22082 (EX1 3 AWG Cu / 1 AWG Al — its dwMinA = 100 constant is the 230.79(C) floor 230.42(B) applies, asserted in the test suite; EX2 2 AWG Cu), pickConductor31016 (EX3 1/0 Cu, EX4 1/0 Cu at 140 A, EX5 bare 1/0 Cu) and derate31015 (EX5 4/0 Cu, 151.34 A derated), nextStdBreaker (EX6 disconnect interlock). The 125% (EX3), 100%-of-140 A (EX4), and the 0.70 × 0.94 derate (EX5) are the code's rules applied to the cores' table values. Zero hand math.