10.5 Information Technology Equipment Rooms & Busways

10.5 Information Technology Equipment Rooms & Busways

Quick Reference: The ICC E3 outline describes Miscellaneous Special Equipment as covering signs, information technology rooms, and wiring and equipment for fire protection systems, including fire pumps, and the Raceways, Cables, and Bus Ducts job task explicitly names bus ducts. Signs and fire pumps have their own sections; this section carries the remaining two — NEC Article 645 (Information Technology Equipment) and NEC Article 368 (Busways).

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1. Article 645 Is Optional — and All-or-Nothing (NEC 645.3, 645.4)

Article 645 is a permissive alternate, not a mandatory overlay. A data center, server room, or network closet may always be wired under the ordinary rules of Chapters 1 through 4. Article 645 exists to relax certain rules — most importantly the plenum and cable rules for the space under a raised floor — but only if the room qualifies.

NEC 645.4 lists the conditions, and every one of them must be met before any Article 645 allowance may be used:

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|        NEC 645.4 - ALL CONDITIONS MUST BE MET TO USE ARTICLE 645            |
+-----------------------------------------------------------------------------+
|  1. A disconnecting means complying with 645.10 is provided.                |
|  2. All information technology equipment is LISTED.                          |
|  3. The room is occupied by, and accessible to, only those personnel needed  |
|     for maintenance and functional operation of the equipment.               |
|  4. The room is separated from other occupancies by fire-resistance-rated    |
|     walls, floors, and ceilings with protected openings.                     |
|  5. Supply circuits and interconnecting cables comply with 645.5.            |
|  6. Only equipment and wiring associated with the operation of the IT room   |
|     is installed in the room.                                                |
|  7. The HVAC system is dedicated to the IT equipment room, or is provided    |
|     with fire/smoke dampers at the room boundary.                            |
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[!WARNING] The plan review consequence. If any one condition fails — a shared HVAC branch with no damper, a room that doubles as general storage, an unlisted custom power unit, an unrated demising wall — then Article 645 is unavailable and the room reverts entirely to the general Code. In particular, the space beneath a raised floor used for environmental air must then satisfy NEC 300.22(C) rather than 645.5(E), which usually means metal raceway, Type MI or MC cable, or plenum-rated cable in place of the DP-type interconnecting cables that Article 645 would have permitted. This is why plans examiners are trained to review 645.4 as a gate before reading anything else in the article.

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2. The Remote Disconnecting Means (NEC 645.10)

The defining safety requirement of Article 645 is a firefighter-usable kill switch. NEC 645.10 requires a means to disconnect:

1. Power to all electronic equipment in the information technology equipment room or in a designated zone within the room, and
2. Power to all dedicated heating, ventilating, and air-conditioning systems serving the room or designated zone, and it must cause all required fire and smoke dampers to close.

The controls must be grouped and identified, and located at readily accessible locations at the principal exit doors. Where a zone approach is used, the boundary of each zone must be identified and the disconnect must be labeled to the zone it controls.

The Code recognizes a limited relief in 645.10(B) for critical operations data systems: an approved means to disable the remote disconnect is permitted where the room has an approved fire suppression system, an emergency power off is not desirable for continuity of critical operations, and qualified personnel with documented procedures are on site.

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3. Supply Circuits and Under-Floor Wiring (NEC 645.5)

• Branch-circuit conductors supplying one or more units of information technology equipment must have an ampacity of not less than 125 percent of the total connected load (645.5(A)).
• Interconnecting cables for IT equipment are permitted to be listed DP-type cables (DP, DP-2, DP-3) under a raised floor when the room qualifies under 645.4 (645.5(E)).
• The space under a raised floor used for environmental air is permitted to contain the wiring methods listed in 645.5(E), provided the raised floor is of suitable construction and the area under it is accessible.
• Abandoned cable — installed cable that is not terminated at equipment and not identified for future use with a tag — must be removed (645.5(G)), which is the same accessible-space rule found in Articles 725, 760, and 800.

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4. Busways (NEC Article 368)

A busway is a factory-assembled grounded metal enclosure containing bare or insulated conductors, usually copper or aluminum bars, rods, or tubes. Plans examiners see them on riser diagrams in high-rises, in manufacturing plants over machine lines, and increasingly in data halls as an overhead plug-in distribution spine.

Where busways may and may not be used

Overcurrent protection and the reduction rule

NEC 368.17(A) requires busways to be protected against overcurrent in accordance with the ampacity of the busway.

NEC 368.17(B) — Reduction in ampacity. Overcurrent protection is not required at the point of reduction where the busway is reduced in ampacity, provided both of the following are true:

• The smaller busway does not exceed 50 ft (15 m) in length, and
• It has an ampacity at least equal to one-third the rating or setting of the overcurrent device next back on the line.

This is structurally the same idea as the 240.21(B)(2) 25-foot feeder tap rule, with a longer length allowance because the busway is a totally enclosed, mechanically protected assembly.

NEC 368.17(C) — Feeder or branch circuits. Where a busway is used as a feeder, devices or plug-in connections for tapping off feeder or branch circuits from the busway must contain the overcurrent devices required for the protection of the tapped conductors — the fusible or circuit-breaker plug-in unit is the protection.

NEC 368.30 — Support. Busways must be securely supported at intervals not exceeding 5 ft (1.5 m) unless otherwise designed and marked. A riser detail that shows 10 ft support spacing without a manufacturer's marking permitting it is a correction item.

5. Worked Plan Review: Data Hall and Overhead Busway Spine

Submittal: A 6,000 sq ft data hall on the third floor of an office building. Drawings show:

1. A raised access floor with listed Type DP-2 interconnecting cables run beneath it.
2. The room's HVAC taken from the building's general variable-air-volume system with no dampers indicated at the demising wall, and the demising partitions shown as standard non-rated metal-stud-and-gypsum construction.
3. A single EPO pushbutton in a locked electrical closet down the corridor.
4. An 800 A plug-in busway spine feeding rack PDUs, reduced to a 250 A busway for a 60 ft branch run to a secondary rack row, with no overcurrent device at the reduction.
5. Busway hangers detailed at 8 ft on center, with no manufacturer marking cited.

Findings:

1. 645.4 conditions 4 and 7 fail. Non-rated demising construction and a shared HVAC system with no fire/smoke dampers mean the room does not qualify for Article 645. Consequently the DP-2 cables under the raised floor are not permitted — that space is an air-handling space and must comply with NEC 300.22(C). Either upgrade the construction and HVAC to qualify, or respecify the under-floor wiring methods.
2. 645.10 fails on location. Even if the room qualified, the disconnecting means controls must be readily accessible at the principal exit doors, not in a locked closet down the corridor. Also, the design shows no means of disconnecting the dedicated HVAC and closing dampers.
3. 368.17(B) fails on both tests. One-third of the upstream 800 A device is $800 \div 3 = 266.7\text{ A}$, and the reduced busway is only 250 A — below the ampacity floor. Independently, the 60 ft run exceeds the 50 ft length limit. Either add an overcurrent device at the point of reduction, increase the reduced busway to at least 267 A, or shorten the run below 50 ft.
4. 368.30 fails. 8 ft hanger spacing exceeds the 5 ft default. Provide the manufacturer's listing documentation permitting the greater spacing, or add intermediate supports.

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6. Plans Examiner Verification Checklist: Article 645 and Article 368

• 645.4 gate: All seven conditions confirmed on the drawings before crediting any Article 645 allowance — listed equipment, restricted occupancy, rated separation with protected openings, dedicated or damper-protected HVAC, compliant supply circuits, and a 645.10 disconnect.
• Disconnect scope: Disconnects all electronic equipment AND the dedicated HVAC, and closes required fire/smoke dampers (645.10).
• Disconnect location: Grouped, identified, readily accessible at the principal exit doors; zone boundaries identified where zones are used.
• Branch circuits: Ampacity not less than 125 percent of total connected load (645.5(A)).
• Under-floor wiring: DP-type cables credited only where the room qualifies; otherwise 300.22(C) methods specified.
• Abandoned cable: Removal note present (645.5(G)).
• Busway location: Not in hoistways, classified locations, wet/damp or outdoor locations, or where subject to severe physical damage, unless identified or specifically approved (368.12).
• Busway protection: Overcurrent device sized to busway ampacity (368.17(A)); any reduction satisfies both the 50 ft length limit and the one-third ampacity floor (368.17(B)).
• Busway taps: Plug-in devices contain the overcurrent protection for the tapped conductors (368.17(C)).
• Busway support: Intervals not exceeding 5 ft unless the assembly is designed and marked otherwise (368.30).