Quick Hits

Episode 11 — Transformer Taps, High-Bay Buildings, and Outdoor Taps

Covers: 240.21(B)(3)–(5)

Hook: Tapping conductors that feed a transformer has its own math — and there's a special rule just for tall manufacturing buildings.

Slide 2: For taps feeding a transformer (primary + secondary combined ≤25 ft): the primary tap needs ampacity at least 1/3 of the feeder OCPD, the secondary needs ampacity at least that same 1/3 value multiplied by the primary-to-secondary voltage ratio, the combined primary+secondary length (minus any ampacity-protected portion) stays under 25 ft, both sets need physical protection, and the secondary terminates in a single OCPD sized to the conductor ampacity.

Slide 3: High-bay manufacturing buildings over 35 ft tall get an extended tap allowance — up to 25 ft horizontal / 100 ft total, under qualified-personnel supervision, ampacity at least 1/3 of the feeder OCPD, single-OCPD termination, physical protection, no splices, minimum 6 AWG copper/4 AWG aluminum, no penetrating walls/floors/ceilings, and the tap made at least 30 ft off the floor. Outdoor taps get unlimited length as long as they're protected from damage, terminate in a single OCPD, and that OCPD/disconnect sits in a readily accessible spot — outside, or inside nearest the point of entrance.

Quiz: How tall must a manufacturing building be at the walls to qualify for the extended high-bay tap rule?
Answer: Over 35 ft (11m).

CTA: Follow — transformer secondary conductor protection rules are next.

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