Article 645: Information Technology Equipment

 

By Mike Holt for EC&M Magazine

 

The requirements for IT rooms seem counterintuitive, until you look closely.

You may have noticed a shut off switch just outside an Information Technology (IT) room. You may wonder who in their right mind would install a backup power system for a critical operations space like an IT room and then put a shutoff switch near the door to that room. Does the fact that the NEC requires such an arrangement mean we’ve found an error in the NEC?

Actually, it’s not an error. The reason for this requirement would be very clear to you, if you were part of a fire response team arriving at the scene with your water hose. Shutting off the main power prevents electrocution in the rest of the building; but inside the IT room you would face energized loads supplied by the UPS. Without an exterior switch, you would need to enter the room to de-energize the loads. Fire personnel don’t have time to search for sources of power—and any guesswork could prove lethal. Because of this, the signage required by 702.8(A) explaining the location of the UPS is simply not adequate. Emergency response personnel need to enter the IT room without wasting any time.

So, what about loss of IT function? During a fire, that’s the least of your concerns. During other times, you can reduce the chance of unauthorized shutdowns with breakaway locks and proper signage.

Compliance with Article 645 involves more than installing an exterior shutoff switch. In addition to protecting fire personnel, Article 645 seeks to reduce the spread of fire and smoke by requiring such things as fire-resistant walls and separate HVAC systems for IT rooms. And a large percentage of Article 645 addresses a common IT room feature: the raised floor.

 

When  Article 645 Applies

So, what is an IT room? The NEC does not define this, but NFPA 75, Standard for the Protection of Electronic Computer/Data-Processing Equipment, gives us some insight. An IT room is an enclosed area specifically designed to comply with the construction and fire protection provisions of NFPA 75.

So, NFPA 75 defines an IT room and describes the construction requirements of the room, and Article 645 gives us the electrical requirements for an IT room.  Does this mean that if you have IT equipment you must create an NFPA 75 and NEC 645 compliant IT room?  No.  An IT room is not required. Rather, an IT room is something that may be desired by the designer or by the owner. Because it allows less stringent wiring methods than would normally be required, it is often desired, but never required.

Article 645 applies only to wiring and equipment located within an IT room that complies with 645.4—not to all wiring associated with IT equipment [645.1]. Article 645 covers equipment, power-supply wiring, and interconnecting wiring of IT equipment and systems in an IT room, but only if that room:

• Has a disconnecting means compliant with 645.10.
• Has a dedicated heating/ventilating/air-conditioning (HVAC) system, and is separated from other areas of the occupancy.
• Contains only listed IT equipment.
• Is occupied only by persons needed for the maintenance and operation of IT equipment.
• Is separated from other occupancies by fire-resistant rated walls, floors, and ceilings with protected openings.

But what if you don’t want to comply with the rules above?  Simple.  Don’t call it an IT room, and follow the rest of the NEC.  Just be mindful that you will not be able to take advantage of the allowances of Article 645. If you want to reap the benefits of an IT room, however, you will have to follow 645.

 

Supply Circuits and Interconnecting Cables.

Each branch-circuit conductor for data-processing equipment must have an ampacity [Article 100] not less than 125 percent of the total connected load [645.5].

In addition to hard wiring IT equipment, you can connect data-processing equipment to a branch circuit by either a flexible cord or a cord set assembly, as long as you follow these two rules:

• A flexible cord must be no longer than 15 ft, with an attachment plug.
• A cord set assembly, where run on the surface of the floor, must be protected against physical damage.

To interconnect data processing units, use cables listed for IT equipment. Where exposed to physical damage, the interconnecting cables must be protected by a means approved by the AHJ.

You can install receptacles and run power cables, communications cables, connecting cables, and interconnecting cables under raised floors. But you can do so only if the installation meets these conditions:

• Construction. The raised floor must be of suitable construction and the area under the floor must be accessible.
• Wiring methods. Branch-circuit wiring methods must be securely fastened in place per 300.11.
• Raceways. You must also install the branch circuits for receptacles or hard wired equipment in one of the following kinds of raceway: 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, nonmetallic surface raceway, flexible metal conduit, liquidtight flexible metal conduit, liquidtight flexible nonmetallic conduit, Type MI cable, Type MC cable, or Type AC cable (Figure 645-1). You can use nonmetallic raceways within the raised floor area because this space is neither subject to physical damage nor required to comply with the environmental airspace requirements of 300.22(C). Although it seems strange to install nonmetallic raceways in an air handling space, it is not prohibited because the air does not communicate with the rest of the building.  When you think about it, if there is a fire inside of the IT room the noxious gases emitted by nonmetallic wiring methods will only affect the IT itself, which is not occupied by people on a regular basis [645.4(4)].
• Ventilation. Ventilation in the underfloor area must be for the IT room only and arranged so air circulation will cease upon the detection of fire or products of combustion.
• Protection. Openings in raised floors must protect the cables against abrasions.
• Cables. You must use Type DP (Data Processing) cable, except for:

• Cables enclosed in a raceway.
• Interconnecting cables listed with equipment manufactured prior to July 1, 1994, and installed with that equipment.
• Signal or communications cables of the following types: Type TC [Article 336]; Types CL2, CL3, and PLTC [Article 725]; Types NPLF and FPL [Article 760]; Types OFC and OFN [Article 770]; Type CM [Article 800]; Type CATV [Article 820].

Signaling and communications cables installed within the raised floor area in an IT room aren’t required to be plenum rated (Figure 645-2).

Conductors with green or green with one or more yellow stripes, insulated 4 AWG and larger, and marked “for use in cable trays” or “CT use” are permitted for equipment grounding (bonding) of the raised floor parts.

• Abandoned cables. Remove these, unless they are in metal raceways.

You know to secure branch circuit supply conductors in place [300.11 and 645.5(D)(2)], but what about IT cables? Article 645 does not require you to secure power, communications, connecting, or interconnecting cables that are part of listed IT equipment (Figure 645-3). You may decide to secure them in place for other reasons, and the NEC certainly won’t stand in the way of doing that.

If signaling and communications cables extend beyond the IT room, install them per the applicable article [645.6]:

• Signaling circuits, Article 725.
• Fire alarm circuits, Article 760.
• Fiber optic cable, Article 770.
• Communications circuits, Articles 800 through 820.
• If wiring systems penetrate the fire-resistant room boundary, seal them per 300.21.

Disconnecting Means

Earlier, we mentioned an exterior shutoff. What exactly are the requirements?

A disconnecting means must disconnect power to IT equipment in the IT room and to dedicated HVAC systems that serve the room. When you have a UPS in an IT room, you must install a disconnecting means per 645.10. This must disconnect power to all UPS systems within the IT room—and it must disconnect all supply and output circuits, and the battery, from its load [645.11].

The control(s) for the disconnecting means must be grouped, identified, and located so as to be readily accessible at the principal exit doors. You can use a single means to control both the electronic equipment and HVAC systems. If you use a button as a means to disconnect power, pushing the button “in” must disconnect the power.

The typical means of establishing the control function of the disconnect is through the use of a normally open (N.O.) momentary pushbutton at each principal exit door. Pressing the emergency button closes the contacts and opens the shunt-trip circuit breaker(s), thereby turning off all power.

 

Grounding (Bonding)

Metal parts of an IT room must be grounded (bonded) to an effective ground-fault current path, per Part VI of Article 250, with an equipment grounding (bonding) conductor of a type specified in 250.118 [250.4(A)(3)].

If an IT room has isolated ground receptacles, ensure they are grounded (bonded) to an effective ground-fault current path per 250.146(D) and 406.2(D). If they are “grounded” to a separate ground rod and not to an effective ground fault current path, they are an electrocution hazard and probably a source of electrical noise. They also violate all accepted electrical standards including the NEC [250.4(A)(5)].

 

Two Goals

Some requirements of Article 645 seem to conflict with the purpose of having an IT room to begin with. But remember, the NEC isn’t an engineering manual—it’s a people and property protection standard [90.1].

IT rooms have special requirements for two reasons:

1. To protect fire personnel from backup power sources.
2. To reduce the spread of fire and smoke.

As you perform design and installation work for IT rooms, always keep these two goals in mind. Doing so will help you correctly interpret and apply Article 645.