NEC 430.72 + 430.75 — Motor Control Circuit Protection + Disconnection

How to protect the control circuit — the low-voltage wires that feed the starter coil, the 24 V transformer secondary, the interlocks — and where it must be disconnected. 430.72 (the tapped-control-circuit rule, Table 430.72(B)'s three columns, and the five 430.72(C) transformer-protection paths), plus 430.75 (the two-device disconnecting means, the immediate-adjacency rule, the >12-conductor remote exception), 430.71 (scope), 430.73 (physical damage), 430.74 (the ground-fault-must-not-start-the-motor rule). The third in the motor trilogy: after 430.22/430.52 (branch conductors + OCPD) and 430.32/430.36 (overload). 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 these sections are (and why the control circuit gets its own rules)

The previous two motor articles sized the branch circuit (430.22 conductors at 125% of table FLC; 430.52 OCPD at 250% etc.) and the overload device (430.32 at 125/115% of nameplate). But a motor circuit is really two circuits: the high-current branch that feeds the motor, and the low-current control circuit that operates the controller — the 24 V (or 120 V) wires from the control transformer secondary through the pushbuttons, interlocks, and to the starter coil. The control circuit carries maybe 1–3 amperes; the branch might carry 100. They need different protection rules, and that is what Article 430 Part VI (Motor Control Circuits) provides:

• 430.71 — scope. Part VI "contains modifications of the general requirements and applies to the particular conditions of motor control circuits."
• 430.72 — "How is the control circuit protected?" The main rule. A tapped control circuit (the common case: control circuit tapped from the load side of the branch OCPD) is not a branch circuit, and its conductors are protected either by a separate OCPD (430.72(B)(1), Table 430.72(B) Column A) or by the branch OCPD itself (430.72(B)(2), Columns B/C — 400%/300% of ampacity). 430.72(C) handles the control-circuit transformer (five paths, including the <50 VA no-protection shortcut).
• 430.73 — physical damage. Where damage to the control circuit would be a hazard, the conductors outside the control device go in raceway or are otherwise protected.
• 430.74 — electrical arrangement. Where one control conductor is grounded, the circuit must be arranged so a ground fault remote from the controller will not start the motor and will not bypass shutdown/safety devices.
• 430.75 — "Where does it get disconnected?" The disconnecting means may be two devices (power + control), and where separate they must be immediately adjacent — with the >12-conductor and hazardous-opening remote exceptions, warning signs required. 430.75(B): the control transformer in the enclosure goes on the load side of the control disconnect.

The one distinction that drives Part VI: the control circuit is tapped from the branch OCPD's load side, so the branch OCPD already "sees" every short/ground fault on the control conductors. The whole of 430.72(B) is a bookkeeping exercise: when can the branch OCPD's rating (sized for the MOTOR) be larger than the control conductors' ampacity without violating conductor-protection principles? Answer: up to 400% (Columns B) or 300% (Column C) — because the control circuit's normal current is a tiny fraction of the branch current, so a fault on it produces near-full branch-current fault levels that the OCPD will clear. EX1–EX4 make the columns concrete.

430.71 — General (the scope of Part VI)

2017 (verbatim on disk)

Two sentences of scope: Part VI modifies the general requirements for the specific conditions of motor control circuits. Everything below is that modification — most of it in 430.72 (protection) and 430.75 (disconnection).

430.72 — Overcurrent Protection of Motor Control Circuits

430.72(A) General — the tapped control circuit rule (2017, verbatim on disk)

Read the first sentence slowly, because it is the architecture of the whole section: the control circuit is tapped from the load side of the branch OCPD. That single fact does three things: (1) the branch OCPD is upstream of the control conductors, so it interrupts every short/ground fault on them; (2) the control circuit is expressly not a branch circuit (so Article 210's branch rules don't apply); (3) it "shall be protected against overcurrent in accordance with 430.72" — the section that follows. The third sentence covers the other-than-tapped case (e.g. a control circuit fed from elsewhere): those follow Article 725 (725.43 in 2017; 724.43 in 2023) or the Chapter 9 small-conductor notes — the low-voltage power/remote-control circuit rules.

430.72(B) Conductor Protection — the two paths + Table 430.72(B) (2017, verbatim on disk)

Two paths, in the order the code presents them:

1. (B)(1) Separate Overcurrent Protection. If the branch OCPD can't be used under (B)(2), put a separate device in the control circuit — and its rating must not exceed Column A of Table 430.72(B). This is the 5 A (or 3 A) control fuse / small breaker you see on most starters. Column A ≈ the conductors' own ampacity, so the separate device protects the conductors the usual way.
2. (B)(2) Branch-Circuit Overcurrent Protective Device. Or ride the control conductors on the branch OCPD itself. It then provides only short-circuit/ground-fault protection, and its rating may exceed the control conductors' ampacity — but only within the table: Column B if the conductors stay inside the motor control equipment enclosure, Column C if they extend beyond it. Columns B/C are 400%/300% of ampacity — the mathematical expression of "the branch OCPD is sized for the motor, and that's acceptable for the control conductors."

Two Exceptions worth knowing. Exception No. 1 (fire pumps and the like): where opening the control circuit would create a hazard, the conductors need only short/ground protection and may ride the branch OCPD — this is the code-level reason fire-pump control wiring is allowed to depend on the branch device. Exception No. 2: a two-wire transformer secondary (the classic 120/24 V control transformer) may be protected on the primary side, with the primary device rated not over (Table 430.72(B) value for the secondary conductor) × (Vsecondary/Vprimary) — the reflected-protection shortcut.

Table 430.72(B) — Maximum Rating of Overcurrent Protective Device in Amperes (2017 on disk; 2023 = Table 430.72(B)(2), values identical)

How to read it: Column A caps the separate device at the conductors' ampacity (14 AWG Cu → 15 A, 12 AWG → 20 A, 10 AWG → 30 A; 18 AWG → 7 A, 16 AWG → 10 A). Column B (conductors inside the enclosure) lets the branch OCPD run to 400% of ampacity — 14 AWG Cu → 100 A, 12 AWG → 120 A, 10 AWG → 160 A. Column C (conductors leaving the enclosure) drops to 300% — 12 AWG → 60 A, 10 AWG → 90 A. The aluminum columns appear from 12 AWG up (the 18/16 AWG rows are copper only). "Larger than 10" uses the Note formulas directly: B = 400% of the free-air (Table 310.17) 60 °C ampacity, C = 300% of the in-raceway (Table 310.16) 60 °C ampacity. EX4c shows the Note-3 computation for 8 AWG (300% × 40 A = 120 A ≥ 100 A branch OCPD → OK).

430.72(C) Control Circuit Transformer — five paths (2017, verbatim on disk)

Five ways to protect the control transformer, in the order you'd check them in the field: (C)(3) first — if it's under 50 VA, integral with the controller, and in the enclosure, no separate OCPD is needed at all (the primary OCPD, impedance, or inherent means suffice). (C)(4) — if the rated primary current is under 2 A, a primary device at not more than 500% of the rated primary current is permitted (EX6b: 200 VA at 120 V → 1.667 A rated primary → 500% cap = 8.33 A, so any device ≤ 8.33 A — a small 5 A or 8 A primary fuse — is permitted; note the cap, not a size). (C)(2) — the general transformer rules of 450.3 (secondary protection, 250% rule, etc.). (C)(1) — if it's feeding a Class 1/2/3 circuit, those articles' own rules govern (724.30–724.52 for power-limited; 725 Part II for Class 2/3 in 2023). (C)(5) — the catch-all. And the Exception: fire-pump-type circuits where opening would be hazardous omit OCPD entirely (mirroring 430.72(B) Exception No. 1).

430.73 — Physical Damage (2017, verbatim on disk)

A "where damage would be a hazard" section — the code's way of saying the control wiring isn't the structural steel. Remote control conductors outside the control device: raceway, or other protection.

430.74 — Electrical Arrangement of Control Circuits (2017, verbatim on disk)

The safety-logic rule: if the control circuit has a grounded conductor, a single ground fault away from the controller must not be able to start the motor or defeat a shutdown device. In practice this is why control circuits are usually arranged with the grounded conductor on the "safe" side of the contacts — a fault from the ungrounded conductor to ground should drop the coil, not energize it.

430.75 — Disconnection of Motor Control Circuits

430.75(A) General — the two-device rule + adjacency (2017, verbatim on disk)

The disconnecting means for a motor control circuit may be two devices: the power-supply disconnect (the branch OCPD or motor-circuit switch that de-energizes the motor + controller) and the control-circuit disconnect (the small switch/fuse block that de-energizes the 24 V circuit). When both are needed, they must sit immediately adjacent — so an operator opening one knows the other is right there. Two remote exceptions: No. 1 (the big-station case: >12 control conductors to disconnect makes one adjacent block impractical — remote allowed with qualified-persons access + permanently located warning signs identifying each remote disconnect), and No. 2 (opening the control disconnect could itself be dangerous — e.g. it drops a load mid-operation — remote allowed under the same two conditions).

430.75(B) Control Transformer in the Enclosure (2017, verbatim on disk)

If the control transformer lives in the controller's enclosure, it must be downstream of the control-circuit disconnect: open the control disconnect, and the transformer's secondary (the live 24 V) de-energizes too. Otherwise you'd have a disconnect that "opens the control circuit" while a live secondary still sits in the box.

The edition history, verified line by line

Bottom line: the numbers never moved. Every cell of Table 430.72(B), the 400%/300% Note formulas, the 50 VA and 2 A/500% transformer thresholds, and the 12-conductor adjacency threshold are identical in 2017 and 2023. What moved is bookkeeping: the 2023 Article 724/725 split (725.43 → 724.43; 430.72(C)(1) restructured), the table's renumber to 430.72(B)(2) with the 310.16/310.17 note re-cites, and the "controller" → "motor controller" terminology pass in 430.75(A)/(B). A 2017 design note citing "Table 430.72(B), Column C, 60 A on 12 AWG Cu" is exactly right in substance in the 2023 code (the table is now 430.72(B)(2)). 2014 not on disk (no 2014 claim).

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

Every number below is produced by the shipped cores in app.js (nextStdBreaker(), pickConductor31016(), smallConductorCap(), T31016 — node-invoked this session via compute_art40.js) and is asserted in the public test suite (test/run_tests.js in the public repo). Table 430.72(B) values are transcribed verbatim from the on-disk 2017 scan (35/35 programmatic checks) and identical in the 2023 CSV. The Table 310.16 values used for the Note-1/Note-3 cells come from the shipped T31016 (60 °C column: 14 AWG = 15 A, 12 AWG = 20 A, 10 AWG = 30 A, 8 AWG = 40 A).

EX1 — 10 AWG Cu control conductors inside the enclosure, 30 A branch OCPD: ride the branch device (430.72(B)(2), Column B)

The everyday case: the 24 V control wiring never leaves the box, so the branch OCPD protects it. Column B's 160 A cap (400% of the 40 A free-air 60 °C ampacity of 10 AWG Cu) is far above any branch OCPD you'd see on a starter with 10 AWG control wiring — the branch device wins, no control fuse needed. (Note: 10 AWG's Column A is only 30 A — a separate device would have to be ≤ 30 A; that's why the separate-fuse path looks small even though the conductors are 10 AWG.)

EX2 — 12 AWG Cu control conductors run in conduit to a remote station, 30 A branch OCPD (430.72(B)(2), Column C)

Same wiring, different path: because the conductors leave the enclosure, the tighter Column C applies (60 A = 300% of the 20 A in-raceway ampacity of 12 AWG Cu). A 30 A branch OCPD still fits. EX3 shows the boundary.

EX3 — 12 AWG Cu beyond the enclosure, 60 A branch OCPD: at the limit

"Shall not exceed" includes the equal case: a 60 A branch OCPD is exactly the Column C value for 12 AWG Cu, so it is permitted — but the next standard size up (70 A, from the shipped STD_BREAKERS list) would fail, and you'd need EX4's resolution.

EX4 — 12 AWG Cu beyond the enclosure, 100 A branch OCPD: fails both paths — and the fix (430.72(B)(1) + Note 3)

The classic "the motor got bigger" scenario. The branch OCPD (100 A) now exceeds Column C for 12 AWG (60 A). You cannot simply put a 100 A fuse in the control circuit — Column A caps a separate device at the conductors' own ampacity (20 A for 12 AWG). The code's answer is to upsizer the conductors: at "larger than 10 AWG," Note 3 = 300% of the in-raceway ampacity, so 8 AWG Cu → 3 × 40 A = 120 A ≥ 100 A, and the branch OCPD again protects the control conductors. (A 15 A or 20 A separate control fuse would also be a legal alternative — but then it protects only up to its rating, and the control circuit still needs the (C) transformer rules to line up.)

EX5 — 40 VA control transformer, integral, in the enclosure: no OCPD (430.72(C)(3))

The most common control transformer in the field — a 40 VA 120/24 V unit riveted to the starter frame — needs no control-circuit OCPD of its own: the branch OCPD upstream of the primary, the transformer's own impedance, or other inherent means are all permitted. This is why so many small starters have no visible control fuse at all.

EX6 — 300 VA transformer (2.5 A primary): (C)(4) is NOT available → 450.3 or 725 (430.72(C))

The 2-ampere boundary in (C)(4) is a rating test, not a margin test: at 2.5 A the 500% shortcut is off the table, and the transformer falls back to the general 450.3 secondary-protection rules (or the Class 1/2/3 rules if it feeds a power-limited/remote-control circuit). The secondary sizing itself is an ordinary ampacity job: 12.5 A → 14 AWG Cu in the 60 °C column (the 240.4(D) cap on 14 AWG is 15 A — right at the ampacity, as the core reports).

EX6b — the (C)(4) positive case: the same 120/24 V transformer at 200 VA: primary current 200 VA ÷ 120 V = 1.667 A < 2 A → (C)(4) applies, and it permits a primary device rated or set at not more than 500% × 1.667 A = 8.333 A. That is a cap, not a target: the largest standard fuse at or below it is 8 A, so an 8 A primary fuse is permitted — a 10 A fuse would exceed the 8.333 A cap and is not allowed under (C)(4). (The cap is stated from the code's 500% formula directly; the shipped core's STD_BREAKERS list starts at 15 A, which is the branch-breaker series and is not the right device class for a transformer primary.)

Gotchas

• "Tapped from the load side" is what unlocks everything. 430.72(B)(2) only works because the control circuit taps the branch OCPD's load side — the OCPD is upstream and clears every control-circuit fault. If you feed the control circuit from some other place, (A) sends you to 725.43 (2017) / 724.43 (2023) or the Chapter 9 notes instead.
• Column A is tiny for a reason. The "separate protection" path (430.72(B)(1)) caps the device at the conductors' ampacity — 14 AWG Cu → 15 A, 12 AWG → 20 A, 10 AWG → 30 A. The 5 A/3 A fuses people see are because the 24 V circuits use 18/16/14 AWG (Column A: 7/10/15 A). You cannot bolt a 30 A breaker onto 14 AWG control conductors as "separate protection." The big numbers (100/120/160 A) are Columns B/C — the branch-OCPD path only.
• Within vs. beyond the enclosure changes the cap (400% → 300%). The same 12 AWG Cu conductors: 120 A (Column B, in the box) vs. 60 A (Column C, leaving the box). Run the control wiring out to a remote station and the branch OCPD may have to shrink — or the conductors must grow (EX4).
• "Larger than 10 AWG" is a formula, not a table row. Column B = 400% of the free-air ampacity (Table 310.17 in 2023; 310.15(B)(17) in 2017), Column C = 300% of the in-raceway ampacity (Table 310.16; 310.15(B)(16)). EX4c: 8 AWG Cu → 3 × 40 A = 120 A.
• The (C)(4) 2-ampere test is on the RATED primary current, exact. 1.9 A qualifies, 2.1 A does not — and the device must be ≤ 500% of that rated primary current (a CAP, not a target). A 24 V/300 VA transformer (2.5 A primary) is out; a 200 VA (1.667 A) is in at 8.33 A → any device ≤ 8.33 A (e.g. a 5 A or 8 A primary fuse) is permitted; 10 A would exceed the cap.
• 50 VA, integral, in the enclosure = no OCPD at all (430.72(C)(3)). All three conditions: rated less than 50 VA, integral part of the controller, located within the controller enclosure. Miss one and the transformer needs real protection (450.3 or the Class 1/2/3 rules).
• 430.75(A): two disconnects must be immediately adjacent. The power disconnect and the control disconnect, separate devices, must sit next to each other — except >12 control conductors (remote OK with qualified-persons access + permanent warning signs) or hazardous-opening cases (Exception No. 2, same conditions).
• 430.75(B): transformer on the LOAD side of the control disconnect. If the 24 V transformer is in the controller enclosure, opening the control disconnect must kill its secondary too. A transformer wired on the line side leaves live 24 V in the box with the disconnect open.
• 430.74's ground-fault logic is a one-way rule. With a grounded control conductor, a remote ground fault must NOT start the motor and must NOT bypass shutdown devices. Arrangement (which side of the contacts the grounded conductor feeds) is what enforces this — it's a wiring-logic check, not a device rating.
• The 2023 renumber traps. "Table 430.72(B)" → "Table 430.72(B)(2)"; the note's "310.15(B)(17)/(16)" → "310.17/310.16"; "725.43" → "724.43"; 430.72(C)(1) now splits power-limited (724.30–724.52) from Class 2/3 (725 Part II). Values unchanged — a pre-2023 spec is still correct in substance, just cite the 2023 numbers.
• "430.78" does not exist in Part VI. Part VI is 430.71–430.75; Part VII (controllers) starts at 430.81. The "430.72/430.78" pairing in some study materials is a mis-citation — the disconnecting-means section is 430.75.

The method, step by step

1. Confirm the tap. Is the control circuit tapped from the load side of the motor branch OCPD? Yes → 430.72(B) applies. No → 725.43 (2017) / 724.43 (2023) or Chapter 9 notes.
2. Choose the protection path (430.72(B)). Separate device (B)(1) → rate it ≤ Column A (the conductors' ampacity). Or branch OCPD (B)(2) → check the branch OCPD rating against Column B (in-enclosure) or Column C (beyond) of Table 430.72(B). Larger-than-10-AWG conductors: 400% free-air / 300% in-raceway 60 °C formulas.
3. Check the exceptions. Fire-pump/hazardous-opening → conductors need only short/ground protection on the branch device (Exception No. 1). Two-wire transformer secondary → primary-side protection at (Table value) × (Vsec/Vprim) (Exception No. 2).
4. Handle the control transformer (430.72(C)). <50 VA + integral + in enclosure → (C)(3) no OCPD. Rated primary < 2 A → (C)(4) ≤ 500% of rated primary. Otherwise → (C)(2) 450.3 or (C)(1) Class 1/2/3 rules (724/725 in 2023). Exception: hazardous-opening circuits omit OCPD.
5. Run the conductors (430.73/430.74). Remote control conductors in raceway or protected where damage would be a hazard; ground the control circuit (if you ground one conductor) so a remote ground fault cannot start the motor or bypass shutdowns.
6. Place the disconnection (430.75). Two devices (power + control) → immediately adjacent, unless >12 conductors (remote + qualified access + warning signs) or hazardous opening (Exception No. 2). Control transformer in the enclosure → load side of the control disconnect.
7. Quote both, with the edition. "Control circuit: 14 AWG Cu, 24 V, tapped from the load side of the 30 A branch OCPD; protected by the branch OCPD per 430.72(B)(2), Column B (100 A cap, 30 A ≤ 100 A); control transformer 40 VA integral — no OCPD per 430.72(C)(3); control disconnect adjacent to the motor-circuit switch per 430.75(A). 2017/2023 values identical; 2023 table renumbered 430.72(B)(2), 725.43 → 724.43."

FAQ

Q: What protects the wires in my motor's control circuit?
A: 430.72(B). Either a separate OCPD ≤ Column A of Table 430.72(B) (the conductors' ampacity — 14 AWG Cu → 15 A, 12 AWG → 20 A), or the motor's branch OCPD itself, if its rating ≤ Column B (conductors inside the enclosure, 400% of ampacity) or Column C (conductors beyond, 300%).

Q: Why is there a 5-amp fuse in my starter's control circuit?
A: That's the 430.72(B)(1) separate protection for the low-voltage conductors — Column A caps it at their ampacity (18/16/14 AWG Cu → 7/10/15 A), so 3 A or 5 A devices are typical. Starters without one are using the 430.72(B)(2) branch-OCPD path (Columns B/C).

Q: Can the motor's main breaker protect the control conductors?
A: Yes — 430.72(B)(2): short/ground protection only, with the OCPD rating ≤ Column B (within enclosure) or Column C (beyond). The branch OCPD is sized for the motor, and the 400%/300% multipliers are what make that acceptable for the small control conductors.

Q: Does my control transformer need overcurrent protection?
A: 430.72(C) gives five paths: (C)(1) 724/725 Class 1/2/3 rules; (C)(2) 450.3; (C)(3) NO OCPD for <50 VA integral transformers in the controller enclosure; (C)(4) ≤500% of rated primary for rated primary <2 A; (C)(5) other approved means. Fire-pump-type circuits omit OCPD (Exception).

Q: Where must the control disconnect go?
A: 430.75(A): two devices (power + control) must be immediately adjacent — remote only under Exception No. 1 (>12 conductors, qualified-persons access, permanent warning signs) or No. 2 (hazardous opening). 430.75(B): a control transformer in the enclosure goes on the load side of the control disconnect.

Q: What changed between 2017 and 2023?
A: Nothing numeric. Table values identical (35/35 checks); table renumbered 430.72(B)(2); 725.43 → 724.43; 430.72(C)(1) restructured to the 724.30–724.52 / 725 Part II split; 430.75(A) exception items (a)/(b) → (1)/(2) + "met" + "motor controller"; notes re-cite 310.17/310.16 (the 2020 ampacity-table rename).

Free, in-browser, no account. The branch OCPD and conductor picks this article cross-references run the same shipped cores (430.52 / 430.22 / Table 310.16) that computed the examples above.