Quick Hits

Article 398 (Part 1 of 2)
Open Wiring on Insulators!

SLIDE 1 — Scope & Uses Permitted (398.1, 398.10)
🏗️ WHAT IS OPEN WIRING ON INSULATORS?
An EXPOSED wiring method — NOT permitted to be concealed by the building structure or finish. Permitted indoors/outdoors, dry/wet locations, and corrosive vapors — as long as the insulation from Table 310.4(1) suits that environment. NOT for temporary construction-site lighting/power, but IS permitted for agricultural building lighting/power and for services (230.43).
✅ WHERE YOU CAN USE IT (398.10)
Only in industrial or agricultural establishments, on systems ≤1000V ac / 1500V dc:
1️⃣ Indoors or outdoors
2️⃣ Wet or dry locations
3️⃣ Where subject to corrosive vapors
4️⃣ For services

SLIDE 2 — Uses Not Permitted & Exposed Work (398.12, 398.15)
⛔ WHERE YOU CAN'T USE IT
Concealed by the building structure — period.
🔧 EXPOSED WORK RULES (398.15)
🔹 Dry locations, not exposed to damage → can enclose in flexible nonmetallic tubing, ≤4.5m (15 ft) continuous lengths, strapped every ≤1.4m (4½ ft)
🔹 Entering damp/wet/corrosive spaces → need drip loops, then pass through noncombustible insulating tubes
🔹 "Exposed to physical damage" = anything within 7 ft of the floor. Protect crossing conductors with: guard strips (≥1 in. thick), a running board (≥1/2 in. thick with side protection), boxing with a cover, or RMC/IMC/PVC/RTRC/EMT

SLIDE 3 — Framing, Clearances & Attics (398.17, 398.19, 398.23)
🪵 THROUGH FRAMING (398.17)
Conductors must be separated from walls/floors/wood members by noncombustible insulating tubes/bushings — EACH conductor gets its own separate tube.
📏 CLEARANCES (398.19)
> 50 mm (2 in.) from metal raceways, piping, or other conductors — or separated by a fixed nonconductor. Route conductors OVER piping subject to leaks/moisture where practical.
🏚️ UNFINISHED ATTICS (398.23)
🔹 Accessible by stairway/ladder → along or through bored holes in framing; runs within 7 ft of the floor need running boards (not required if run along the SIDES of framing)
🔹 Not accessible → same rule, with an exception for pre-existing buildings with <3 ft headroom (wiring on rafter/joist edges)

SLIDE 4 — Support Basics + Final Exam (398.30(A)–(B) preview)
📏 SMALLER THAN 8 AWG (398.30(A))
Rigidly supported on noncombustible insulators — supports within 150mm (6 in.) of a tap/splice, within 300mm (12 in.) of a dead-end to a lampholder/receptacle, and at intervals < 1.4 m (4½ ft).
📏 8 AWG AND LARGER (398.30(B) preview)
Can span up to 4.5m (15 ft) with spacers maintaining> 65 mm (2½ in.) between conductors — more support rules coming in Part 2!

🧠 FINAL EXAM QUESTION FOR ARTICLE 398 (Part 1)
Q: Per 398.15(C), conductors within how many feet of the floor are considered exposed to physical damage?
A) 5 ft
B) 6 ft
C) 7 ft
D) 8 ft
(Drop your final answer 👇)

Article 398 Part 1 = DONE ✅ Part 2 drops next — mill construction spans, industrial support, tie wires & devices! ⚡ #JoshTheSparky #NEC2026 #ElectricianLife

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