Quick Hits

EPISODE 12 — High-Temperature, Messenger-Supported & Bare/Covered Ampacity Tables — Article 310 FINALE (310.18–310.21)

Slide 1 — Hook "Final episode of Article 310! Wrapping up with the specialty ampacity tables — high-temperature insulation, messenger-supported conductors, and bare/covered conductors in free air."

Slide 2 — 310.18 & 310.19 — the high-temperature tables

• 310.18: conductors rated 150°C/200°C/250°C in raceway or cable, 40°C ambient, 3 or fewer current-carrying conductors — covers specialty types like Z, FEP/FEPB/PFA/SA, and PFAH/TFE (the latter using nickel or nickel-coated copper).

• 310.19: same insulation types and temperature tiers, but for single conductors in FREE AIR at 40°C ambient — again running meaningfully higher than the raceway/cable equivalents, same pattern as 310.16 vs. 310.17.

Slide 3 — 310.20 & 310.21

• 310.20: ampacities for conductors supported ON A MESSENGER (a support wire/cable system) — 75°C/90°C rated, 40°C ambient, 3 or fewer single-insulated conductors.

• 310.21: bare or covered conductors in free air — this one uses different baseline CONDITIONS entirely: a 2 ft/sec wind velocity assumption, 80°C total conductor temperature, 40°C ambient. Covers bare/covered copper AND bare AAC (all-aluminum-conductor) types.

Slide 4 — Quiz + CTA Q: "Table 310.21 (bare/covered conductors in free air) assumes what wind velocity condition?" A) No wind (0 ft/sec) B) 2 ft/sec C) 5 ft/sec D) 10 ft/sec

✅ Answer: B — 310.21: based on a 610 mm/sec (2 ft/sec) wind velocity assumption.

CTA: 🎉 That's a wrap on ALL of Article 310 — Conductors for General Wiring! Follow for more daily quick-hit study notes as we move into the box/enclosure articles (312 and 314) next.

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