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Figure 01
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For EC&M Magazine
By Mike Holt, NEC® Consultant
How do you limit the spread of fire and smoke in an IT room?
Article 645 provides alternative wiring methods and materials, to those methods and materials required in other chapters of the NEC. This alternative is optional, and it’s for information technology (IT) equipment and systems in an IT equipment room [645.1].
An IT equipment room is an enclosed area specifically designed to comply with the construction and fire protection provisions of NFPA 75, Standard for the Fire Protection of IT Equipment.
Shutoff switch
Article 645 requires a shutoff switch readily accessible from the (main) exit from an IT equipment room [645.10]. This switch allows someone outside the room to shut down power to everything inside (or everything in designated zones inside).
Can this be right? Despite having a UPS and taking every precaution against a power outage, the IT system is deliberately vulnerable to a shutdown from a readily accessible switch. What was the Code Making Panel thinking of when they added this requirement?
They were thinking of first responders, such as firefighters. Being able to shut down the power and disconnect the batteries before entering the IT room during a fire allows the rescue team to use fire hoses and other equipment without risking contact with energized equipment. Yes, there’s loss of IT function during the shutdown, but if the room needs fire and rescue teams, that loss is the least of anyone’s problems at that time. The shutdown allows the rescue of people and property.
A breakaway lock can protect the IT room from inadvertent shutdown via this switch. Typically, IT rooms have other protections against unauthorized shutdown. For example, there may be limited (card key) access to the building containing the IT room. And then to the room itself.
Where permitted
Article 645 provides alternative wiring methods to:
• Chapter 3 and Parts I and III of Article 725 for signaling wiring.
• Parts I and V of Article 770 For optical fiber cabling.
These are permitted where all the following conditions are met [645.4]:
(1) A disconnect complying with 645.10 is provided.
(2) A dedicated heating/ventilating/air conditioning (HVAC) system is provided for IT equipment and is separated from other areas of the occupancy.
(3) IT and communications equipment in the IT room is listed.
(4) The room is occupied and accessible only to persons needed for the maintenance and operation of IT equipment.
(5) The IT equipment room is separated from other occupancies by fire resistant rated walls, floors, and ceilings with protected openings.
(6) Only electrical equipment and wiring associated with the operation of the IT room is installed in the room.
This last requirement includes HVAC systems, communications systems (twisted wire, antennas, and coaxial cable) fire alarm systems, security systems, water detection systems, and other related protective equipment [645.4(6) Informational Note.
Data circuits
Data circuits for IT systems are classified as Class 2 or Class 3 circuits per 725.121(A)(4) and must be installed per Article 725 requirements [725.1]. Class 2 or Class 3 circuit conductors installed in the same cable with communications circuits are reclassified as communications circuits, and the cable must be listed as communications cable per725.139(D)(1) and 800.133(A)(1)(c) [645.3(D).
Supply circuits and interconnecting cables
Branch circuit conductors for IT equipment must have an ampacity at least 125 percent of the total connected load [645.5(A)]. IT equipment can be connected to a branch circuit by a power supply cord that is no longer than 15 ft if the cord and attachment plug are listed for use on IT equipment [645.5(B)]:
Cables listed for IT equipment can be used to interconnect IT equipment without the 15 foot cable length limitation [645.5(C)].
If exposed to physical damage, the supply circuits and interconnecting cables must be protected [645.5(D)].
When is it permissible to install the following items under a raised floor? Power cables, communication cables, connecting cables, interconnecting cables, cord and plug connections, and receptacles associated with the IT equipment. Answer: when the area under the raised floor is accessible and any openings minimize the entrance of debris beneath the floor. The installation must comply with 645.5(E)(1) through (3)
Branch-circuit wiring
Branch circuit wiring under a raised floor must be securely fastened in place per 300.11 [645.5(E)(1)(a)].
The following seventeen wiring methods are permitted under a raised floor [645.5(E)(1)(b):
• Rigid metal conduit.
• Rigid nonmetallic conduit.
• Intermediate metal conduit.
• Electrical metallic tubing.
• Electrical nonmetallic tubing.
• Metal wireway.
• Nonmetallic wireway.
• Surface metal raceway with metal cover.
• Surface nonmetallic raceway.
• Flexible metal conduit.
• Liquidtight flexible metal conduit.
• Liquidtight flexible nonmetallic conduit.
• Type MI cable.
• Type MC cable.
• Type AC cable.
• Associated metallic and nonmetallic boxes or enclosures.
• Type TC power and control tray cable.
Under a raised floor, you can use these kinds of power supply cords, interconnecting cables, cables, and conductors [645.5(E)(2)]:
• Power supply cords of listed IT equipment per 645.5(B).
• Interconnecting cables enclosed within a raceway.
• Equipment grounding conductors (EGCs).
• Plenum and nonplenum rated Class 2 and/or Class 3 cables and substitute cables per 725.154(A).
• Listed Type DP cable.
• Plenum and nonplenum rated optical fiber cables [645.5(E)(3)].Figure 01
Cables
Power supply cables, communications cables, connecting, and interconnecting cables that are part of listed IT equipment don’t have to be secured in place where installed under raised floors [645.5(F)].
Informational Note: Raceways and cables that aren’t part of listed IT equipment must be secured and supported per 300.11.
An abandoned cable is one that isn’t terminated to equipment and isn’t identified for future use with a tag [645.2]. The accessible portion of any abandoned cables must be removed unless contained within a raceway [645.5(G)].
Cables identified for future use must be each marked with a tag of sufficient durability to withstand the environment [645.5(H)].
Cable tags must have the following information:
• Date cable was identified for future use.
• Date of expected use.
• Intended future use.
Plenums
These sections and tables apply to wiring and cabling in a plenum space above an IT equipment room [645.3(B)]:
(1) Wiring per 300.22(C).
(2) Class 2 and Class 3 plenum rated cables per 725.135(C) and Table 725.154.
(3) Plenum rated fire alarm cables per 760.53(B)(2), 760.135(C) and Table 725.154.
(4) Plenum rated optical fiber cables per 770.113(C) and Table 770.154(a).
(5) Plenum rated communications cables per 800.113(C) and Table 800.154(a), (b), and (c).
(6) Plenum rated coaxial cables per 820.113(C) and Table 820.154(a).
Disconnecting means
An approved disconnect must disconnect power to all electronic equipment in the IT equipment room and dedicated HVAC systems that serve the room or in designated zones within the room [645.10]. The disconnect must comply with either 645.10(A), or with 645.10 if used for critical operations data systems.
Remote disconnect controls must be at an approved readily accessible location [645.10(A)]. The remote disconnect means for the electronic equipment power and HVAC systems must be grouped and identified. A single means to control both is permitted.
Additional means to prevent unintentional operations of remote disconnect controls are permitted. These include administrative means, such as employee training and limited access.
UPS
A disconnecting means installed per 645.10 must disconnect the UPS systems, their supply and output circuits, and the battery from the load, except for installations and constructions covered in 645.11(1) or (2).
Grounding and bonding
Separately derived power systems used for IT equipment (power distribution units) must be grounded and bonded per 250.30 [645.14]. Exposed metal parts of an IT system must be connected to the circuit equipment grounding conductor (EGC) [645.15].
Where signal reference structures are installed, they must be bonded to the circuit EGC provided for the IT equipment.
If you install isolated ground receptacles, you must connect them to an insulated EGC per 250.146(D) and 406.3(D).
Getting IT (rooms) right
The shutdown switch required by Article 645 is a noticeable exception to normal design principles. That switch poses risk to operations, so think carefully about how to prevent inadvertent or unauthorized operation.
The primary goal of Article 645 is to reduce the spread of fire and smoke. The raised floors common in IT rooms pose challenges to achieving this goal, so this article devotes a fair percentage of its text to raised floor requirements. Fire resistant walls, separate HVAC systems, and other requirements further help to achieve this goal.
Openings into or through fire rated walls, floors, and ceilings for electrical equipment must be firestopped using methods approved by the authority having jurisdiction. The goal here is to maintain the fire resistance rating of the fire rated assembly [645.3(A)].
As with the switch, ask what could go wrong and design accordingly.
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