NEC 460.9 + 460.8 — Power-Factor-Correction Capacitors on Motor Circuits

The capacitor companion to the motor series. The motor trilogy covered the branch circuit (430.22/430.52), the overload (430.32/430.36), and the control circuit (430.72/430.75) — but what happens when you hang a power-factor-correction (PFC) capacitor on a motor circuit to improve the power factor? Two sections own that: 460.8 (how to wire, protect, and disconnect the capacitor — the 135% of rated current conductor rule, the one-third rule for the short lead to the motor, the “as low as practicable” overcurrent device, and the disconnecting means) and 460.9 (the single most-cited gotcha: the motor overload is set for the improved power factor, but the motor circuit conductor is NOT re-sized — the capacitor is disregarded for the 430.22 conductor rating).

The sections, in full (2017)

The four sections that carry a PFC capacitor on a motor circuit, quoted verbatim from the 2017 NEC. 460.8 (conductors, overcurrent, disconnect) and 460.9 (the overload / conductor split) are the core; 460.6 (discharge), 460.10 (grounding), and 460.12 (marking) are the companion rules a capacitor installation must also satisfy.

Why 460.9 is the one that bites people

Think about what a PFC capacitor actually does. A motor is an inductive load: it draws a lagging current, and part of that current is "reactive" power that does no real work. A capacitor connected on the load side supplies that reactive power locally, so the line (the conductors and the overload, upstream of the capacitor) sees a lower current at a higher power factor. That is the whole point of PFC — smaller currents in the feeders, less I²R loss, better utilization.

Here is the 460.9 split, stated plainly:

• The overload moves. The motor overload device sits on the load side of the capacitor, so it now carries the improved-power-factor current (lower than the no-capacitor current). 460.9 says set it for that improved power factor — so you may reduce the setting, and you should, to protect the windings accurately.
• The conductor does not. The motor circuit conductors carry the full motor current over the starting transient, the locked-rotor condition, and any moment the capacitor is switched out. So 460.9 sends the conductor back to 430.22 (125% of the table full-load current) and says to disregard the capacitor. The conductor is sized for the worst case, not the improved case.

The same logic appears in 460.8's two Exceptions: a capacitor on the load side of a motor overload (460.8(B) Exception) or a motor controller (460.8(C) Exception) does not need its separate OCPD or disconnect — the upstream motor device already provides it. That is exactly the configuration 460.9 describes (capacitor load-side of the overload), which is why the two sections are the pair.

The companion sections — 460.6, 460.10, 460.12

A PFC capacitor is not just a current problem. A charged capacitor holds energy, its case can be a shock path, and it must be identified. These three sections close out the installation; all are word-identical 2017 → 2023.

Edition history: 2017 → 2020 → 2023

The headline for this article is good news: the Part I power-factor-correction core is word-identical from 2017 to 2023. 460.8(A), 460.8(B), 460.8(C), 460.9, 460.6, 460.10, and 460.12 did not move a single word across two editions. The edition changes to Article 460 are real but they live in other sections — 460.1 (scope) and the Part II over-1000-V rules — and they are documented below. This article quotes the PFC core once (2017 text) and states it is unchanged in 2023, because that is verifiably true.

The verified-identical core (2017 = 2023, word-for-word)

A normalized machine diff (lowercased, whitespace-collapsed, de-hyphenated, and stripped of the 2023 CSV's list-number and trailing-paren artifacts) of the on-disk 2017 text against the on-disk 2023 CSV returns an exact match for every section in the PFC core:

2020 position — stated, not asserted: no on-disk 2020 full-code text covers Article 460 (the on-disk 2020 scan is a short excerpt; the 2020/2023 viewer is login-gated). So this page documents 2017 → 2023 and does not assert a 2020 word-identity for Article 460. The identity claim rests on the two on-disk full sources (2017 NFPA scan + 2023 CSV), which is the standard this series uses.

2017 → 2023 deltas elsewhere in Article 460 (all verified on disk)

The changes that did land, each pinned to the on-disk text:

Five worked examples (core-computed)

Every ampacity, conductor pick, and overcurrent rating below is computed by the shipped cores under node (compute_art49.js → art49_numbers.json): the capacitor rated current (3-phase kVAR×1000/(√3·V), 1-phase kVAR×1000/V), pickConductor31016 for the conductor pick (Table 310.16, with the 240.4(D) small-conductor note), and nextStdBreaker for the overcurrent / disconnect step-up. Zero hand math. The 5 hp motor FLC comes from Table 430.250 (7.6 A at 460 V).

EX1 — 10 kVAR, 3-phase, 480 V stand-alone PFC bank (a separate circuit, 460.8 A/B/C)

A stand-alone bank (not load-side of a motor overload) needs its own OCPD and its own disconnect, both at 135% of the rated current. 12 AWG Cu carries 20 A at 60 °C — and 240.4(D) independently caps a 12 AWG conductor at a 20 A device, so the 460.8(B) "as low as practicable" 20 A OCPD and the 240.4(D) cap land on the same answer.

EX2 — 5 kVAR, 3-phase, 460 V stand-alone PFC bank

At 60 °C a 14 AWG Cu conductor is rated 15 A, which clears the 8.472 A requirement with margin; 240.4(D) caps 14 AWG at 15 A, so the 15 A OCPD / disconnect is the natural pair. (The 5 kVAR / 460 V bank also reappears in EX5, as the capacitor on the one-third-rule lead.)

EX3 — 5 hp, 460 V, 3-phase motor with a load-side PFC capacitor (the 460.9 split)

This is the trap. The conductor stays at the 430.22 pick — 125% × 7.6 A = 9.5 A → 14 AWG Cu (20 A @ 75 °C) — because 460.9 says to disregard the capacitor for the conductor. Only the overload is set for the improved power factor: with PF lifting 0.80 → 0.95 the line current drops 7.6 → 6.4 A, so the overload protects against the lower, true carrying current instead of the pre-correction value. (The actual overload setting also depends on the 430.32 percent-of-nameplate rules; the 6.4 A here is the improved-PF current the setting is based on.)

EX4 — 2 kVAR, single-phase, 230 V stand-alone PFC bank

Single-phase PFC (common on a 230 V pump or compressor circuit) uses the kVAR×1000/V form — no √3. 2 kVAR at 230 V is a larger current than it looks (8.696 A) because of the low voltage; the 14 AWG Cu / 15 A pair covers it.

EX5 — the one-third rule: the short lead from the motor terminals to the PFC capacitor (460.8(A))

This is the classic one-third-rule case where the other half of 460.8(A) wins. The lead from the motor terminals to the capacitor is allowed to be as small as one-third the motor circuit conductor ampacity (6.67 A here) — but it can never drop below 135% of the capacitor's rated current (8.47 A). Since 8.47 > 6.67, the 135% figure governs and the lead is 14 AWG Cu. On a much larger motor (a big conductor, so one-third is large) the one-third figure would govern instead — which is exactly why the code gives you the larger of the two.

Where 460.9 + 460.8 fit — the capacitor companion to the motor series

• The branch circuit the capacitor sits on: 430.22 + 430.52 (conductors at 125% of FLC; the OCPD) — the 430.22 + 430.52 single-motor branch-circuit article →. 460.9 sends the conductor straight back to 430.22 (EX3).
• The overload 460.9 re-sets: 430.32 + 430.36 (the motor overload device and which conductors it protects) — the 430.32 + 430.36 motor-overload-protection article →. 460.9 tells you the 430.32 setting is based on the improved PF.
• The control circuit of the controller the capacitor can load-side: 430.72 + 430.75 — the 430.72 + 430.75 motor-control-circuit-protection article → (460.8(C)'s Exception references the motor controller).
• The small-conductor cap that bounds the OCPD picks (240.4(D)): the 240.6 standard-ampere-ratings article → and the Table 310.16 ampacity article → (the 240.4(D) cap and the ampacity picks are computed there and used here).

2026 edition (out of scope, flagged honestly): no on-disk source confirms the Article 460 section numbers moved for the 2026 cycle, so this page cites 460.8 / 460.9 as stable across 2017–2023 and presents the 2017↔2023 deltas above. Verify section numbers against the NEC edition adopted in your jurisdiction.

Method, sources & honesty notes

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