4.1 Branch Circuit & Feeder Installation (0301)

Branch Circuits vs. Feeders

A branch circuit (NEC Article 210) is the circuit conductors between the final overcurrent protective device (OCPD) and the outlet(s) it serves — the last link to the utilization equipment. A feeder (Article 215) is the conductors between the service equipment (or a separately derived system) and the final branch-circuit overcurrent device, carrying the aggregate of all downstream branch-circuit loads. Inspectors must distinguish the two because the sizing and protection rules differ in scope: a branch circuit is checked against the single load it feeds, while a feeder is checked against the sum of its branch circuits after demand factors (Article 220). Both must be verified for conductor sizing, voltage rating, identification, and protective device ratings.

Branch Circuit Ratings (210.3, 210.5, 210.6)

210.18 (renumbered from 210.3 in the 2023 NEC) states that branch circuits are rated according to the maximum permitted rating or setting of the overcurrent device, and that branch circuits other than individual branch circuits shall be rated 15, 20, 30, 40, and 50 amperes. The 2023 edition added a 10-ampere branch circuit, but it is deliberately narrow: 210.23 permits a 10 A multiple-outlet branch circuit to supply only lighting outlets, a dwelling-unit exhaust fan on a bathroom or laundry lighting circuit, and a gas fireplace unit on an individual branch circuit — receptacle outlets, fixed appliances, garage door openers, and laundry equipment are expressly excluded.

210.5 requires the ungrounded conductors of different systems in the same premises to be identified by phase or line and system, with the means of identification posted at each branch-circuit panelboard — the reason a 208Y/120 V panel and a 480Y/277 V panel in the same building must carry different, documented color schemes.

210.6 limits branch-circuit voltage, and the limit is stated between conductors, not to ground. In dwelling units and guest rooms or guest suites, 210.6(A) caps the voltage between conductors supplying luminaires and cord-and-plug-connected loads of 1440 VA or less (or less than ¼ hp) at 120 volts. In other occupancies, 210.6(C) permits up to 277 volts to ground to supply listed luminaires — which is exactly why commercial lighting is routinely 277 V and why the same fixture layout in an apartment would be a violation.

Common Branch Circuit Ampacities

Minimum Conductor Size (210.19, 215.2)

210.19(A) requires branch-circuit conductors to have an ampacity not less than the maximum load served and not less than the rating of the OCPD (with permitted adjustments). For continuous loads (those expected to operate at maximum current for 3 hours or more), the conductor ampacity must be at least 125% of the continuous load plus 100% of the noncontinuous load. 215.2(A) applies the same formula to feeders: feeder conductor ampacity must not be less than 125% continuous plus 100% noncontinuous. The difference is scope — the feeder carries the combined load of many branch circuits — not the formula itself.

Termination temperature limits (110.14(C), 215.2(A)(1))

Conductor ampacity must also match the termination temperature rating of the equipment. 110.14(C) — not Article 215 — is the section that limits the ampacity usable at a termination. For equipment rated 100 A or less, or marked for conductors 14 AWG through 1 AWG, use the 60°C column unless the equipment is marked for 75°C. For equipment rated over 100 A, or marked for conductors larger than 1 AWG, use the 75°C column unless the equipment is marked for 90°C. A 90°C-insulated conductor such as THHN may not use its 90°C ampacity at the termination — the 90°C column is a starting point for correction and adjustment only, and the final answer is the lower of the derated value and the termination-limited value.

Identification of Grounded & EGC Conductors (200.6, 250.119)

200.6 requires grounded (neutral) conductors of 6 AWG or smaller to be identified by a continuous white or gray outer finish or by three continuous white stripes. Conductors 4 AWG and larger may be re-identified at terminations with white or gray tape or paint along their entire visible length. 250.119 requires equipment grounding conductors (EGC) to be bare, covered, or insulated and identified by green or green-with-one-or-more-yellow-stripes markings. A conductor with green insulation may not be used as an ungrounded conductor, and a white or gray conductor may not be repurposed as an ungrounded conductor except in specific switch-loop applications. Correct identification is a frequent inspection item because misidentified neutrals and EGCs create shock and fault-clearing hazards.

Multiwire Branch Circuits (210.10)

A multiwire branch circuit (Article 100) has two or more ungrounded conductors with a voltage between them and a neutral with equal voltage between it and each ungrounded conductor. Article 210.4 governs it:

• 210.4(A) General — except as permitted in 300.3(B)(4), all conductors of a multiwire branch circuit must originate from the equipment containing the branch-circuit overcurrent devices. The 2023 NEC tightened this language: the 2020 wording said "the same panelboard or similar distribution equipment," and "similar distribution equipment" was not a defined term.
• 210.4(B) Disconnecting means — each multiwire branch circuit must have a means to simultaneously disconnect all ungrounded conductors at the point where the circuit originates. A listed handle tie or a multipole breaker with a common internal trip satisfies this (240.15(B)(1)). This protects a worker servicing one ungrounded conductor from backfeed through the shared neutral.
• 210.4(C) — multiwire branch circuits shall supply only line-to-neutral loads, with two narrow exceptions.
• 210.4(D) — the ungrounded and neutral conductors of each multiwire branch circuit must be grouped by wire markers, cable ties, or similar means at least once in the panelboard or other point of origination.

The field failure this prevents is an open shared neutral: with the neutral broken, two 120 V line-to-neutral loads end up in series across 240 V, and the lighter load sees far more than 120 V.

Neutral Conductor Sizing (220.61)

The grounded (neutral) conductor of a multiwire or 3-wire circuit is sized for the maximum unbalanced load per 220.61. Because loads on opposite phases partly cancel through the shared neutral, the neutral is often smaller than the ungrounded conductors — but it must never be smaller than the EGC required for fault clearing (250.122) and must carry the maximum unbalanced current. On a 3-phase, 4-wire system with non-linear loads, the neutral may need to be full-size or larger to carry harmonic current.

GFCI & AFCI Protection (210.8, 210.12)

210.8 is written by voltage and location, not by ampere rating — a change candidates who learned the old "15- and 20-ampere" wording get wrong. The current rule covers 125-volt through 250-volt receptacles supplied by single-phase branch circuits rated 150 volts or less to ground, installed in the listed locations. 210.8(A) lists the dwelling-unit locations; 210.8(B) lists the non-dwelling locations, which is the list that matters for the E2: bathrooms, kitchens, rooftops, outdoors, sinks, indoor damp and wet locations, locker rooms with adjacent showers, garages/service bays/similar areas, crawl spaces, unfinished portions of basements, laundry areas, and bathtub/shower spaces. 210.8(D) adds GFCI for the branch circuits or outlets supplying specific appliances such as dishwashers. Section 5.1 covers the non-dwelling list in detail.

210.12 requires arc-fault circuit interrupter protection for 120-volt, single-phase, 15- and 20-ampere branch circuits supplying outlets or devices in the listed dwelling-unit rooms (210.12(A)), in dormitory units (210.12(B)), and in guest rooms and guest suites of hotels and motels (210.12(D)) — the latter two are the ones a commercial inspector actually enforces. Confirm the listed AFCI type is installed at the origin of the circuit.

Voltage Drop (Informational Notes)

Voltage drop is a design issue, not an enforceable NEC requirement for ordinary branch circuits and feeders. The Code's informational material recommends a maximum of about 3% drop on a branch circuit and 5% total on the combined feeder and branch circuit to the farthest outlet. Because informational notes are explanatory and not enforceable (90.5(C)), an inspector cannot red-tag a compliant conductor solely for voltage drop — but the recommendation is followed in practice, and it does become mandatory in a handful of specific articles (for example fire pump feeders and sensitive electronic equipment supplies). Where conductors are increased in size for voltage drop, 250.122(B) requires the equipment grounding conductor to be increased proportionally.

Worked Example — Branch Circuit Sizing

A 20 A, 120 V branch circuit serves a 16 A continuous load (for example, a commercial refrigerator).

• Minimum conductor ampacity per 210.19(A) = 125% × 16 = 20 A. A 12 AWG copper conductor (Table 310.16, 75°C column = 25 A) satisfies this, and the 20 A device is the maximum permitted on 12 AWG copper by the small-conductor rule in 240.4(D) anyway.
• OCPD per 210.20(A) = 125% x 16 = 20 A, so a standard 20 A breaker is selected.
• Because the continuous load (16 A) exceeds 50% of the 20 A circuit rating, no other outlets may be supplied on this circuit, ensuring the rating is never exceeded.
• At 120 V the circuit delivers 20 A x 120 V = 2,400 VA of capacity; the 125% rule limits the connected continuous load to 2,400 / 1.25 = 1,920 VA (16 A), which matches the load.