This article was posted 02/06/2006 and is most likely outdated.

Article 645: Information Technology Equipment
 

 
Topic - NEC
Subject - Article 645: Information Technology Equipment

February 6, 2006 

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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.

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Comments
  • I agree with the interpretation. An article supporting this interpretation can be found at http://www.csemag.com/article/CA6290839.html

    Ron Shapiro
    Reply to this comment

  • Where do you get the idea that the 645.10 disconnecting means would be outside the room? I've never seen that, never had an AHJ ask for it, and can't imagine any IT room owner going for it. Right inside the door is the typical location. Way too much risk of process interruption to have the disconnecting means outside the room.

    David Beach
    Reply to this comment

  • Great timing on this Mike. Had an inpsector yesterday question us on this subject.

    Adam Corbin
    Reply to this comment

  • I missed the mention of the text "exterior shutoff". I also agree that they are typically on the interior of the principal exit doors. Inside the room is better, as it typically is more secure than the exterior to reduce accidental or malicious activation.

    Ron Shapiro
    Reply to this comment

  • Thanks Mike. This was a very good topic and you clarified several things for me regarding IT rooms. There have been many IT rooms required by the AHJ, when the owner only wanted a space to locate a couple of servers.

    Dan Prater
    Reply to this comment

  • Side notes - Under raised floors is typically a rats nest of IT cables, and underfloor fires are not uncommon. PVC insulation on IT cables emits noxious fumes when it burns, and IT rooms used to be fitted with Halon suppressant systems (I don't know if this is still done). Both are a real danger to occupants. The interior "crash bar" door openers and E-stop buttons addressed the need to evacuate quickly and safely. In the mainframe days, IT rooms with raised floors were manned around the clock - I suppose some still are.

    glenn robinson
    Reply to this comment

  • I agree with Mike's interpretation, but there is one other issue that causes a lot of confusion about Article 645 and NFPA 75. Many eople who read NFPA 75 for the first time misinterpret it because most NFPA standards are written to prevent hazards and spread of fire. But, NFPA 75 is written to prevent a fire in the building that is OUTSIDE the IT Room from ENTERING the IT Room and destroying millions of dollars worth of equipment. Thus the fire alarm automatically shuts off the HVAC and closes the fire/smoke dampers to keep fire out, not to keep it in. And the EPO Switch must be activated before the sprinklers not just to prevent electrocution hazards but to allow salvage of the equipment and data after the water damage. The EPO switch is a last ditch effort to shutdown all of the equipment when a fast evacuation of the building is necessary and there is no time for an orderly shutdown.

    While Mike's comment about being able to use relaxed practices in Article 645 is an incentive, the main reasons an owner may be forced to comply with Article 645 and NFPA 75 are economic.

    I once worked on a UPS project for a tenant where the building owner had not installed fire/smoke dampers. TECHNICALLY, Article 645 and NFPA 75 did not apply because the fire/smoke dampers were missing. But the spirit of both codes were followed on the tenant's project for economic reasons.

    Paul A. Harouff, P.E.
    Reply to this comment

  • I one time worked for an elementary school that had me put in a commercial grade light switch so that they could cut the power at the end of the day to the 4 computers and the common disk drive. I also know of an electronics supply firm that has a bunch power relays hooked up to cut the power to all of the office equipment at the end of the day. They had this done after their old building burned to the ground.

    Also, this elementary school had me install a second set of light and exhaust fan switches below the first set so that the younger children could operate them. I also opened up the other wall and lowered the drain pipe for the sink so that I could lop off the top of the sink vanity and lower the sink.

    ----------------

    Halon is no longer being made. This is because chlorine monoxide and bromine monoxide eat the ozone layer for the the same reason that they act as fire extinguishing agents. The way that a fire propogates energy from on molecule of fuel to another is by means of high energy oxygen such as ozone, monatomic oxygen, and excited diatomic oxygen. What ClO and BrO do is that they have multiple oxidation states that can absorb extra oxygen atoms and then harmlessly discharge the energy. Think of Halon as acting like the control rods in a nuclear reactor.

    Back in the old days of carbon tetrachloride fire extingushers the Germans also had a compound named BC with the chemical formula CH2BrCl that would break down into carbon dioxide, bromine monoxide, and chlorine dioxide. This was much safer thatn carbon tet because it would not generate phosgene COCl2 which would destroy people's lungs.

    Mike Cole mc5w at earthlink dot net

    Michael R. Cole
    Reply to this comment

  • Would the plenum area over the ceiling tile in a 645-compliant IT room have the same IT wiring rules as under the raised floor? In other words, could CM or OFCR-rated cable be installed exposed over the ceiling tile if the ceiling plenum is used as the air return for the IT room?

    Thanks, William

    William Wilson
    Reply to this comment

  • I just finished a project with at a utility's control center where the IT room is most critical to the power grid. EPO buttons in a room of this importance are an enormous liability, should someone activate one inadvertently. While the premis is good, this is an application in which we are using Halon as our Fire Protection means and would like to have this equipment running until someone qualified is able to shut it down. I believe this type of application has to be reviewed on a case-by-case basis to appropriately determine the best course of action in terms of safety and operation.

    Dave Holbrook
    Reply to this comment


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