7.3 Feeder and Branch-Circuit Tap Rules

Tap Rules Are Exceptions — Treat Them That Way

On the Arkansas Prov JW exam, tap questions separate candidates who open 240.21 from those who guess “10 feet” from field lore. The general rule is still: protect conductors where they receive their supply. Every tap permission is a measured, conditioned exception. If any condition fails, the tap is not allowed — upsize, relocate the OCPD, or redesign.

Tab 240.21, then the specific subsections: (A) branch-circuit taps, (B) feeder taps, (C) transformer secondary conductors, and related outside/busway permissions as needed.

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General Rule vs Exception Mindset

240.21 opens by requiring overcurrent protection in each ungrounded conductor at the supply point, except as otherwise permitted in 240.21(A) through (H).

Exam translation:

• Default answer: OCPD at the supply end of the conductors.
• Alternate answer path: only if the stem’s length, ampacity ratio, termination device, and installation conditions match a listed tap rule.
• Never combine half of the 10-ft rule with half of the 25-ft rule.

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Branch-Circuit Taps — 240.21(A)

240.21(A) points to tap permissions for branch circuits, including references to rules such as those historically associated with fixture taps, outlet/device taps, and other branch applications (open the current 2023 text for exact cross-references and length limits).

Prov themes for branch taps:

• Shorter tap lengths than many feeder tap permissions.
• Tap conductors must be suitably protected and must terminate in equipment/OCPD arrangements the section allows.
• Do not use feeder 10-ft / 25-ft ratios on a stem that clearly says branch-circuit tap.

If the stem mentions taps to luminaires or to a single device on a branch circuit, stay in 240.21(A) and any referenced 210/240 fine print — not 240.21(B).

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Feeder Taps — 240.21(B) Overview

240.21(B) is the high-yield feeder tap cluster. Common exam permissions include:

Critical shared ideas across the common indoor feeder taps:

1. Tap conductors leave a larger feeder protected by an upstream OCPD.
2. Length is strictly limited for the rule you claim.
3. Tap ampacity must meet the fraction of the upstream device rating stated in that subsection (1/10 or 1/3 are the classic indoor pairs).
4. Tap conductors generally must terminate in a single circuit breaker or set of fuses that will limit the load on those taps (sized to protect the tap conductors as required).
5. The tap must be installed in ways that protect it from physical damage and meet enclosure/termination conditions in the text.

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The 10-Foot Feeder Tap — 240.21(B)(1)

Classic Prov pattern (confirm every condition in your book):

• Tap conductors not over 10 ft long.
• Ampacity of the tap conductors not less than one-tenth of the rating of the overcurrent device protecting the feeder being tapped.
• Tap conductors do not extend beyond the switchboard, switchgear, panelboard, disconnecting means, or control devices they supply (as worded).
• Tap conductors are enclosed in a raceway from the tap through the enclosing cabinet/enclosure (per the section’s installation language).
• The tap terminates in an OCPD sized for the tap conductor ampacity rules of the subsection.

Worked ratio check: Upstream feeder breaker = 400 A. One-tenth = 40 A. Tap conductors must have ampacity ≥ 40 A (and still meet all other 10-ft conditions). A 25-ft run cannot hide under the 10-ft rule even if the ampacity ratio is fine.

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The 25-Foot Feeder Tap — 240.21(B)(2)

The 25-ft feeder tap raises the ampacity floor:

• Length not over 25 ft.
• Ampacity of tap conductors not less than one-third of the rating of the overcurrent device protecting the feeder.
• Additional installation and termination conditions in 240.21(B)(2) must all be met (including how/where the tap is installed and that it terminates in a single breaker/set of fuses protecting the taps).

Worked ratio check: Upstream device = 300 A. One-third = 100 A. Tap ampacity must be at least 100 A. Using the 10-ft rule’s one-tenth value (30 A) on a 25-ft tap is a classic wrong answer.

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Outside Feeder Taps and Other 240.21(B) Paths

When the stem places the tap outdoors, open 240.21(B)(3) (and related outside language) instead of forcing indoor 10/25-ft numbers. Outside taps often allow different length treatment when conductors are outside the building (except at the termination point) and terminate in a single OCPD limiting the load to the tap ampacity — but only with the outdoor rule’s full condition set.

Likewise, busway taps and long industrial taps have their own subsections. If the stem does not match, do not invent a hybrid.

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Transformer Secondary Conductors — 240.21(C)

240.21(C) covers transformer secondary conductors. These are not the same as feeder taps from a 480 V feeder to a panel.

Exam discipline:

• Primary protection does not automatically protect secondary conductors.
• Secondary conductor length and ampacity rules are specific (including common 10-ft and 25-ft secondary permissions with their own ampacity relationships to transformer secondary current).
• Separately derived system grounding/bonding may also appear in the same stem — answer the asked part with the correct article.

If the one-line shows a transformer, start at 240.21(C), not 240.21(B)(1).

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What Taps Are Not

Clarify these field myths for Prov:

• A tap is not “any splice on a feeder.”
• A subfeed lug kit or cable from a panelboard is not automatically a 240.21 tap permission — check whether conductors are protected at their supply.
• Feeder tap rules do not delete equipment grounding requirements; EGCs still follow 250.122 based on the OCPD protecting the circuit as applicable.
• Continuous-load sizing still matters for the OCPD that terminates the tap (§7.4).

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Timed Open-Book Workflow for Tap Stems

1. Identify: branch tap, feeder tap, or transformer secondary.
2. Open the matching 240.21 subsection only.
3. Check length first — if length fails, the rule fails.
4. Check ampacity ratio (1/10, 1/3, or secondary-specific).
5. Check termination in a single OCPD (or other required termination).
6. Check raceway/physical protection and “does not extend beyond” language.
7. Only then pick the answer.

This sequence is faster than reading all of Article 240 under time pressure.