Quick Hits

Article 371 (Part 2 of 2)
Flexible Bus Systems — Installation, Terminations, Supports & Marking!

SLIDE 1 — Installation Requirements (371.18)
🔧 INSTALLATION MUST-HAVES
🔹 Installed under design engineering supervision + per manufacturer's instructions, including supporting/securing — documentation available to the AHJ (371.18(A))
🔹 Physical damage → approved protective means required (barriers, guards, or elevation) (371.18(B))
🔹 Transversely routed through walls → permitted if the in-wall section is continuous and protected; fire-resistant-rated walls follow 300.23 (371.18(C))
🔹 Through dry floors/platforms → permitted vertically; fire-resistant-rated floors/ceilings follow 300.23 (371.18(D))
🔹 Through floors/platforms in WET locations → permitted vertically if curbs (or similar) prevent waterflow through the opening, or the system seals the penetration; fire-rated assemblies still follow 300.23 (371.18(E))

SLIDE 2 — Terminations (371.20)
🔌 TERMINATION RULES
🔹 Must terminate with fittings/connectors LISTED for flexible bus systems (371.20(A))
🔹 Connection to distribution equipment must satisfy ONE of the following (371.20(B)):
1️⃣ Listed and marked BY the equipment as an acceptable termination means
2️⃣ Listed and identified FOR that specific equipment as an acceptable termination means
3️⃣ Include a transition box (as part of the listed system) to interface between the bus system and the equipment

SLIDE 3 — Securing, Supporting & Short Circuit Rating (371.30, 371.40, 371.60)
📏 SUPPORT SPACING
Flexible insulated bus conductors: horizontal runs ≤ 3 ft (900mm), vertical runs ≤ 1½ ft (450mm) — unless the product listing permits otherwise.
🔩 FITTINGS & BRACKETS
🔹 Associated fittings must be part of the LISTED system (371.30(A))
🔹 Support brackets secure to the building structure — or to other fittings that are secured to the building structure (371.30(B))
🔹 Support trays are permitted (as listed associated fittings) and do NOT have to be continuous (371.30(C))
⚡ SHORT CIRCUIT CURRENT RATING (371.40)
Must be sufficient for the available fault current.
🌎 GROUNDING (371.60)
Conductive associated fitting supports shall be bonded together AND grounded.

SLIDE 4 — Marking (371.120) + Final Exam Question
🏷️ MARKING REQUIREMENTS
🔹 Each section → manufacturer's name/trade designation, voltage rating, current rating — visible after installation
🔹 System nameplate → manufacturer's name/trademark + voltage, phase, current rating, short circuit current rating, and environmental ratings — installed at EACH end, visible after installation (371.120(A))
🔹 Associated fittings → marked as suitable for flexible bus systems (371.120(B))
🔹 Flexible insulated bus → marked along the insulation with manufacturer's name/trademark, voltage, part ID, and insulation temp ratings (371.120(C))
🔹 Environmental marks → applied where listed for specific environments (371.120(D))

🧠 FINAL EXAM QUESTION FOR ARTICLE 371 (Part 2)
Q: Per 371.30, what is the maximum support interval for a VERTICAL run of flexible insulated bus conductors (unless the listing says otherwise)?
A) 900mm (3 ft)
B) 450mm (1½ ft)
C) 1.2m (4 ft)
D) 600mm (2 ft)
(Drop your final answer 👇)

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