NEC 250.32 — Separate Buildings & Structures Supplied by a Feeder

How to ground a detached building or structure fed from your panel — the grounding electrode (250.32(A)), the single-branch-circuit Exception, the EGC run with the supply (250.32(B)), the neutral-bonding prohibition, the remote-disconnect rules (250.32(D)), and the GEC sizing (250.32(E)). Verbatim 2017 and 2023, the verified edition deltas, and six worked examples — every number computed by the shipped calculator core. Last updated 2026-09-04 (written for PanelWright v1.16).

What 250.32 is (and the one question it answers)

250.32 answers one question: how do I ground a building or structure that is NOT the service — a detached garage, a shed, a pool pump house, a workshop, a separate structure fed by a feeder or branch circuit(s) from your main panel? That is all it does. It is the separate-building grounding rule, distinct from the service grounding (250.28 / 250.30 / 250.32 all under Article 250) and from the separately-derived-system grounding (250.30 — a transformer or generator). The section title is "Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s)" — verified identical across 2014/2017/2020/2023.

Because the section is short but dense, it is constantly misapplied in the field: people bond the neutral in the garage (250.32(B)(1) forbids it), skip the electrode when they needed one (250.32(A)), or size the GEC on the EGC instead of the largest ungrounded conductor (250.32(E) / 250.66). This article covers 250.32(A)–(E) in full across the editions on disk, because the 2017→2023 deltas (especially 225.32→225.31(B)) are where citations go stale.

250.32(A) — Grounding Electrode: the requirement + the Exception

2017 (verbatim on disk)

2023 (verbatim on disk)

Two rules, one exception:

1. The requirement: a building or structure supplied by a feeder(s) or branch circuit(s) shall have a grounding electrode (or system) installed per Part III of Article 250. The grounding electrode conductor(s) are connected per 250.32(B) or (C). (2017 adds the explicit sentence "Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed" — dropped in 2023 as the "installed in accordance with Part III" language now implies it.)
2. The Exception (the answer to "do I need a ground rod?"): a grounding electrode is not required if (1) only a single branch circuit — including a multiwire branch circuit — supplies the building or structure, AND (2) that circuit includes an equipment grounding conductor (the green/bare wire). This is the "small outbuilding fed by one circuit" case. The moment you add a second circuit or a feeder, the electrode is back.

The exception is the most common source of both over-building (installing a ground rod where none is needed) and under-building (skipping the electrode when a second circuit is added later). The test is always: how many circuits, and is there an EGC? One circuit + EGC → no electrode. Two circuits or a feeder → electrode required.

250.32(B) — Grounded Systems: the EGC with the supply + the neutral-bonding prohibition

250.32(B)(1) — Supplied by a Feeder or Branch Circuit (the core rule)

This is the heart of the section, and it carries the single most common inspection failure in detached buildings:

• Run an EGC with the supply. The equipment grounding conductor (green/bare, per 250.118) shall be run with the supply conductors and connected to the building/structure disconnecting means AND to the grounding electrode(s). Sized by 250.122 (Table 250.122) on the OCPD rating — not the neutral load, not the GEC.
• The neutral shall NOT be bonded. "Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s)." This is the prohibition. Bonding the neutral at the separate building creates a parallel neutral return path — fault current can flow on the neutral instead of the EGC, breakers trip randomly, and the ground-fault protection is defeated. This is why you do NOT connect the white to the green or to the ground rod in the garage.
• Exception No. 1 (previous-edition grandfathering). For installations made under previous editions (pre-1998, when the neutral WAS permitted to serve as the ground-fault return path), the grounded conductor may continue to serve that role IF all three conditions hold: (1) no EGC is run with the supply, (2) no continuous metallic paths bonded to the grounding system in each building involved, (3) no ground-fault protection on the supply side. If it IS used for grounding, the grounded conductor must be sized for the larger of 220.61 (calculated neutral load) or 250.122 (EGC). This is the "old wiring where the white does double duty" trap — and it is the ONLY path where the neutral is bonded at the separate building.
• Exception No. 2 (separately-derived system tie). If system bonding jumpers are installed per 250.30(A)(1) Exception No. 2 (a separately derived system at the building), the feeder grounded circuit conductor at the building SHALL be connected to the EGCs, the GEC, and the enclosure of the first disconnecting means. This is the case where the garage has its own transformer — a different installation from the ordinary feeder-fed building.

250.32(B)(2) — Supplied by a Separately Derived System

The separately-derived-system branch — if the garage has its own transformer (a derived system), the grounding follows 250.30(A) instead. The overcurrent-protection-at-the-origin condition selects which rule applies. This is the companion to the 250.26 + 250.30 separately-derived-systems article →.

250.32(C) — Ungrounded Systems

Ungrounded systems (no grounded/neutral conductor at all — e.g. a 3-phase ungrounded feeder): same EGC requirement, but the grounding electrode(s) are ALSO connected to the disconnecting means (there is no neutral to keep off of). The separately-derived branch mirrors (B)(2) with 250.30(B) instead of 250.30(A).

250.32(D) — Remote Disconnecting Means: the neutral-bonding prohibition made explicit

2017 (verbatim on disk)

2023 (verbatim on disk)

250.32(D) is where the neutral-bonding prohibition is stated most explicitly for the remote-disconnect case (the disconnect is located AWAY from the building it serves — a panel in the house that powers the garage via a remote-operated or reachable disconnect). Three conditions, all must be met:

1. (D)(1) — the prohibition: the grounded (neutral) conductor SHALL NOT be connected to the grounding electrode, to equipment, or to the EGC at the separate building. This is the same rule as 250.32(B)(1) but stated for the remote-disconnect configuration.
2. (D)(2) — the EGC: an EGC is run with the circuit conductors and connected to the existing electrode(s), or a new electrode is installed if the building is supplied by more than one branch circuit.
3. (D)(3) — the junction box: the EGC-to-electrode connection is made in a junction box, panelboard, or similar enclosure located immediately inside or outside the separate building.

The edition delta that matters: 2017 cites 225.32 ("Location" — a standalone section) Exceptions 1 and 2; 2023 cites 225.31(B) Exceptions 1 and 2. The 2023 NEC merged the former standalone 225.32 "Location" section INTO 225.31(B) (2017 had 225.31 "Disconnecting Means" + 225.32 "Location" as two sections; 2023 has 225.31(A) "Means" + 225.31(B) "Location + Exceptions" as one section). The 700/701 references also renumbered (700.12(B)(6)→700.12(D)(4), 701.12(B)(5)→701.12(D)(3)). A 2017 design note citing "250.32(D) per 225.32" is stale in the 2023 code — the citation is now "250.32(D) per 225.31(B), Exceptions 1 and 2." The rule itself (neutral not bonded at the remote structure) is unchanged.

250.32(E) — Grounding Electrode Conductor sizing

The GEC (the wire from the ground rod / electrode to the disconnect / EGC at the building) is sized by 250.66, keyed on the largest ungrounded supply conductor — NOT the neutral, NOT the EGC. This is the most common sizing error: people size the GEC on the EGC or the neutral instead of the largest hot conductor. Full table and the electrode-type caps in the 250.66 / separately-derived-systems article →.

The edition history, verified line by line

The core rules are unchanged across all three editions: (1) a separate building fed by a feeder or multiple branch circuits needs a grounding electrode (single-branch-circuit + EGC exception), (2) an EGC is always run with the supply and sized by 250.122, (3) the neutral is never bonded at the separate building (except the pre-1998 grandfather in Exception No. 1), (4) the GEC is sized by 250.66 on the largest ungrounded conductor. The deltas are wording and citation: 250.32(A) restructured, 250.32(B)(1) Exception No. 1 sizing reworded, and 250.32(D)'s 225.32→225.31(B) citation (the 2023 merge of the standalone 225.32 "Location" section into 225.31(B)). 2014 not on disk (no 2014 claim); 2026 renumber flagged on-page.

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

Every number below is produced by the shipped cores in app.js (reqBreakerA(), nextStdBreaker(), neutralLoad22061(), pickConductor31016(), smallConductorCap(), node-invoked this session) and is asserted in the public test suite (test/run_tests.js in the public repo). The EGC table (250.122) and GEC table (250.66) are code — encoded as data (transcribed once from the on-disk article 22 / article 24, 3-way live-verified in prior sessions, asserted by the test suite). Table 310.16 values are base values: 30 °C ambient, ≤3 current-carrying conductors.

EX1 — the everyday 60 A detached-garage feeder (the canonical case)

A detached garage fed by a 2-pole 60 A breaker, 120/240 V, from the main panel. Single building, more than one branch circuit (the 2-pole counts as a feeder here) → electrode REQUIRED.

A clean 60 A garage: 6 AWG Cu feeder, 8 AWG Cu EGC, 8 AWG Cu GEC to a ground rod (or existing water pipe / Ufer / ring). The neutral (if the garage has one) is NOT bonded to the rod or the EGC. The EGC and GEC happen to be the same size here (8 AWG Cu), but that is a coincidence of this case — EX2 shows they diverge.

EX2 — 100 A shop feeder (GEC smaller than EGC — the common confusion)

A workshop fed by a 100 A feeder from a 200 A service. The GEC comes out SMALLER than the EGC — the exact opposite of what most people expect.

Here the EGC is 6 AWG Cu (250.122, 100 A OCPD) but the GEC is 8 AWG Cu (250.66, 3 AWG Cu largest ungrounded). The GEC is smaller than the EGC. This is correct — they use different tables keyed on different things. The EGC is keyed on the OCPD rating (100 A); the GEC is keyed on the largest ungrounded conductor (3 AWG Cu, which falls in the "2 AWG or smaller" band → 8 AWG Cu GEC). Never size the GEC on the EGC — size it on the largest hot conductor per 250.66.

EX3 — the 250.32(A) Exception: single branch circuit + EGC (NO electrode needed)

A small outbuilding (a shed, a tool room, a pump house) fed by a single 20 A branch circuit from the main panel, with the EGC (green wire) in the cable. This is the Exception case — no grounding electrode required.

One circuit + an EGC in the cable = no ground rod, no GEC. Just run the 12 AWG Cu EGC back to the origin and you are done. The moment you add a second circuit (or convert to a feeder), the electrode and GEC come back. This is the most common over-building case in the field: people install a ground rod for a single-circuit outbuilding when the Exception already covers it.

EX4 — 250.32(B)(1) Exception No. 1: the pre-1998 "white does double duty" trap

An old installation (pre-1998) where the neutral (white) was originally permitted to serve as the ground-fault return path to a separate building, and no EGC was run with the supply. The neutral may continue in that role ONLY if all three Exception No. 1 conditions hold — and if it does, the neutral must be sized for the larger of 220.61 (calculated neutral load) or 250.122 (EGC).

The neutral must carry the 220.61 calculated load (92.5 A here) — the larger of the two requirements. This is the trap: in a pre-1998 installation where the white is the ground-fault return, the neutral cannot be undersized. If you are REWIRING (adding an EGC), the Exception No. 1 no longer applies and the neutral must be isolated from the ground at the building. This is the "old garage wiring" case that trips up inspectors most often.

EX5 — 250.32(D) remote disconnecting means: the neutral is NOT bonded at the garage

The disconnect for the garage is located remotely (in the house panel, reachable per 225.31(B) Exception No. 1 or 2 — single management, documented safe switching, or a 685.1 photovoltaic building). 250.32(D) applies. The critical rule: the neutral is NOT bonded to the electrode or EGC at the garage.

The remote-disconnect case is the most common inspection failure: the electrician bonds the neutral to the ground rod at the garage because "it's a separate building." 250.32(D)(1) says no — the neutral connection to the electrode/equipment/EGC at the separate building "shall not be made." The EGC is run with the circuit and bonded at the ORIGIN (the house), not at the remote structure. The electrode at the garage is connected to the EGC via the GEC, in a junction box or similar enclosure at the garage — but the neutral stays off of everything at the garage.

EX6 — 200 A feeder (large shop / machine): both tables climb, the GEC cap becomes relevant

A large machine shop fed by a 200 A feeder. The EGC and GEC both climb the tables; at very large sizes the GEC cap at 3/0 Cu (250 kcmil Al) becomes the governing limit.

At 200 A, the EGC is 4 AWG Cu (250.122, 200 A row) and the GEC is 4 AWG Cu (250.66, 3/0 Cu largest ungrounded → "2/0 or 3/0" band). They agree here. At even larger sizes (over 1100 kcmil Cu ungrounded), the GEC table caps at 3/0 Cu (250 kcmil Al) — the GEC never gets bigger than that, regardless of how large the feeder is. The EGC table, by contrast, keeps scaling (up to 500 kcmil Cu at 4000 A). Full table in the 250.122 article → and the 250.66 article →.

Gotchas

• "Bond the neutral in the garage" — wrong (in a modern installation). 250.32(B)(1): "Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s)." The neutral is NOT bonded at the separate building. The only exception is the pre-1998 grandfather (Exception No. 1) — and even then the neutral must be sized for the larger of 220.61 or 250.122.
• "Do I need a ground rod?" — usually yes, but not always. 250.32(A): a building fed by a feeder or more than one branch circuit needs an electrode. The Exception: a single branch circuit (including multiwire) + an EGC = no electrode needed. The test is always: how many circuits, and is there an EGC?
• EGC ≠ GEC — different tables, different keys. The EGC (green wire with the supply) is sized by 250.122 on the OCPD rating. The GEC (to the ground rod) is sized by 250.66 on the largest ungrounded conductor. In a 100 A case: EGC 6 AWG Cu, GEC 8 AWG Cu — the GEC is smaller. Never size the GEC on the EGC.
• The GEC can be smaller than the EGC. EX2 shows it: 100 A feeder, EGC 6 AWG Cu, GEC 8 AWG Cu. This is correct and expected — the tables are keyed on different things. Do not "upsize the GEC to match the EGC" out of habit.
• The 250.32(D) remote-disconnect case is the most common inspection failure. People bond the neutral at the garage because it is "a separate building." 250.32(D)(1) says the neutral connection to the electrode/equipment/EGC at the separate building "shall not be made." The EGC is bonded at the ORIGIN, not at the remote structure.
• The 225.32→225.31(B) citation is stale in the 2023 code. A 2017 design note citing "250.32(D) per 225.32, Exception 1/2" is dead in 2023 — the standalone 225.32 "Location" section was merged into 225.31(B). The rule is unchanged; the citation moved.
• The 2020 body is not on disk. The on-disk 2020 full-code scan ends at Article 230, so the 250.32 2017→2020 word-diff is not available. The core rules are stable 2017–2023; the verified deltas are 2017→2023 (250.32(A) restructure, 250.32(B)(1) Exc No. 1 reword, 250.32(D) citation). If your jurisdiction adopted 2020, the rule set is the same; the wording is the transitional year between the two on-disk editions.

The method, step by step

1. Count the circuits. Single branch circuit (incl. multiwire) + EGC present → 250.32(A) Exception: no electrode, no GEC. Feeder or two or more branch circuits → electrode + GEC required.
2. Install the electrode. A grounding electrode or system per Part III of Article 250 (rod, ring, Ufer, water pipe, building steel, or other listed). If one already exists (water pipe, Ufer), use it — no new rod needed.
3. Run the EGC with the supply. The equipment grounding conductor (green/bare, 250.118) is run with the supply conductors, connected to the building/structure disconnecting means AND to the electrode(s). Sized by 250.122 on the OCPD rating.
4. Do NOT bond the neutral. The grounded conductor is NOT connected to the electrode, the EGC, or any equipment ground at the separate building. (Exception: pre-1998 installations per 250.32(B)(1) Exception No. 1 — size the neutral for the larger of 220.61 or 250.122.)
5. Size the GEC. The grounding electrode conductor (to the electrode) is sized by 250.66 on the largest ungrounded supply conductor. Apply the electrode-type caps (6 AWG Cu for a rod-only electrode, etc.) — see the 250.66 article →.
6. Quote both. "EGC 8 AWG Cu (250.122, 60 A OCPD), GEC 8 AWG Cu (250.66, 6 AWG Cu largest ungrounded), electrode per 250.32(A), neutral NOT bonded at the garage (250.32(B)(1))." — and the edition.

FAQ

Q: Does a detached garage need a ground rod?
A: Usually yes, but not always. 250.32(A) requires an electrode for a building fed by a feeder or more than one branch circuit. The Exception: a single branch circuit (including multiwire) + an EGC = no electrode needed. The test: how many circuits, and is there an EGC? One circuit + EGC → no rod. Two circuits or a feeder → rod (or other electrode) required.

Q: Can I bond the neutral to the ground in my garage?
A: No — not in a modern installation. 250.32(B)(1): "Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s)." The only exception is the pre-1998 grandfather (Exception No. 1) — and even then the neutral must be sized for the larger of 220.61 or 250.122, and all three Exception No. 1 conditions must hold.

Q: How big is the GEC (ground wire to the rod)?
A: 250.32(E) sizes it by 250.66 on the largest ungrounded supply conductor. 6 AWG Cu feeder → 8 AWG Cu GEC. 3 AWG Cu 100 A → 8 AWG Cu GEC (smaller than the 6 AWG Cu EGC). 3/0 Cu 200 A → 4 AWG Cu GEC. The GEC table caps at 3/0 Cu (250 kcmil Al) for over-1100-kcmil-Cu feeders.

Q: What is the difference between the EGC and the GEC?
A: Two different conductors, two different jobs, two different tables. EGC (green wire with the supply) = fault-current path, sized by 250.122 on the OCPD. GEC (to the ground rod) = earth connection, sized by 250.66 on the largest ungrounded conductor. In a 100 A case: EGC 6 AWG Cu, GEC 8 AWG Cu — the GEC is smaller. Not interchangeable.

Q: Which edition does PanelWright implement?
A: The 2017–2023 rule set for separate-building grounding — the core rules (electrode + Exception, EGC with supply, neutral not bonded, GEC per 250.66) are unchanged. The 2023 wording changes (250.32(A) restructure, 250.32(B)(1) Exc No. 1 reword, 250.32(D) 225.31(B) citation) are documented. The cores use the 2017–2023 Table 250.122 and Table 250.66 (values unchanged across those editions). Verify against the edition adopted in your jurisdiction.

Free, in-browser, no account. The 220.82 service card rolls a real dwelling load up to the feeder current; the 250.32 rules above are the code-side explanation of how to ground the detached building that feeder feeds.