Quick Hits

Article 390 (Part 1 of 2)
Underfloor Raceways — Full Article Breakdown!

SLIDE 1 — Scope & Reconditioned Equipment (390.1, 390.3)
🏗️ WHAT IS AN UNDERFLOOR RACEWAY?
Brings light, power, signal, and communications to desks/benches/tables NOT located near a wall — great with movable partitions, common in large retail and office buildings.
🔌 Raceways, junction boxes, and fittings sit beneath concrete, wood, or other flooring — the wiring between junction boxes and cabinets/outlet boxes can be ANY appropriate Chapter 3 method.
🚫 Reconditioned underfloor raceways are NOT permitted to be installed (390.3(B)).

SLIDE 2 — Uses Permitted & Not Permitted (390.10, 390.12)
✅ WHERE YOU CAN USE THEM
Beneath concrete or other flooring — or in office occupancies, laid flush with the concrete floor and covered with linoleum or equivalent.
⛔ WHERE YOU CAN'T USE THEM
1️⃣ Subject to corrosive vapors
2️⃣ Hazardous (classified) locations — except as permitted by 504.20 and Class I, Division 2 per 501.10(B)(3)
📌 Metal raceways/boxes/fittings need approved material or corrosion protection before going in concrete or severely corrosive areas.

SLIDE 3 — Covering Requirements (390.15)
🧱 HOW MUCH CONCRETE/WOOD ON TOP?
🔹 ≤4 in. wide (half-round or flat-top) → min 3/4 in. concrete or wood cover
🔹 >4 in. but ≤8 in. wide → min 1 in. concrete cover if spaced ≥1 in. apart; min 1½ in. cover if spaced <1 in. apart
🔹 Trench-type, flush with concrete → permitted with removable covers giving protection equal to junction box covers
🔹 Office occupancies: metal flat-top ≤4 in. wide → permitted flush, covered with linoleum (min 1/16 in.) or equivalent. 2–3 raceways installed flush must be contiguous and joined into a rigid assembly.

SLIDE 4 — Conductors: Size, Fill & Ampacity (390.20, 390.22, 390.23) + Final Exam
📏 SIZE LIMIT
No conductor larger than what the raceway is designed for.
📊 FILL LIMIT
Combined cross-sectional area of conductors/cables ≤ 40% of the raceway's interior cross-sectional area.
🌡️ AMPACITY
Adjustment factors from 310.15(C) apply.

🧠 FINAL EXAM QUESTION FOR ARTICLE 390 (Part 1)
Q: Per 390.15(A), half-round and flat-top raceways not over 4 in. wide need at least how much concrete or wood covering above them?
A) 1/2 in.
B) 3/4 in.
C) 1 in.
D) 1½ in.
(Drop your final answer 👇)

Article 390 Part 1 = DONE ✅ Part 2 drops next — splices, discontinued outlets, alignment, markers & junction boxes! ⚡ #JoshTheSparky #NEC2026 #ElectricianLife

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