Article 645 - Code Basics

by Mike Holt for EC&M Magazine

What you don’t know about code requirements for Information Technology Equipment rooms may be shocking.

As the US economy continues to move from being manufacturing-based to being information-based, it is increasingly important to understand the Article 645 requirements for information technology equipment (ITE). Article 645 covers equipment, power-supply wiring, interconnecting wiring, and grounding of information technology equipment and systems in an ITE room. If the equipment is not in an ITE room, Article 645 doesn’t apply. Thus, the first thing you need to know is what an ITE room is.

[645.2] An ITE room meets the following conditions:

  • It has a disconnecting means that complies with 645.10 (which we’ll address in more detail, later)
  • It has a separate HVAC system dedicated for information technology equipment and separated from other areas of the occupancy.
  • The only equipment installed in the room is ITE.
  • The only occupants are people needed for the maintenance and functional operation of ITE.
  • The room is separated from other occupancies by fire-resistant-rated walls, floors and ceilings with protected openings.
  • It is an enclosed area specifically designed to comply with the construction and fire protection provisions of NFPA 75: Standard for the Protection of Electronic Computer/Data Processing Equipment.

If the room doesn’t meet those conditions, other NEC Articles apply, but Article 645 does not. For example, suppose a facility has a grouping of computers for its accounting and Web server systems. But, this room shares an HVAC system with other office space. The installation must meet the requirements of Chapters 1 through 4, but Article 645 does not pertain to it. Remember, the presence of data processing equipment alone does not qualify a room as being an ITE room under the auspices of Article 645.

[645] The branch circuit conductors for data processing equipment must have an ampacity not less than 125 percent of the total connected load. You can connect data processing equipment to a branch circuit by:

  • A flexible cord (maximum 15 ft) and attachment plug, or
  • A cord set assembly. You must protect such an assembly against physical damage, if you run it on the surface of the floor. You can do this with, for example, a cord set guard made just for that purpose.

What if you need to interconnect separate data processing units? You can do that with cables listed for the purpose. As with cord sets, you must protect them from damage if you run them on the floor.

Under Raised Floors

You do not need to use plenum-rated cables for signal and communications, when you install cables within the raised floor area in an ITE room. Under a raised floor, you can use power cables, communications cables, connecting cables, interconnecting cables and receptacles associated with the ITE, provided you meet the following conditions:

  • The raised floor is of suitable construction and the area under the floor is accessible.
  • The branch circuit supply conductors to receptacles or field-wired equipment within the raised floor are in one of the raceway types listed in 645 (d)(2). You can use nonmetallic raceways within the raised floor area in an ITE room because this space is not subject to physical damage and it is not required to comply with the requirements of 300.22(D) for environmental air space. You can install signal and communications cables such as CL2, CM, MP or CATV within the raised floor [645.5(D)(5)(c)].
  • You install the branch circuit supply conductors per the requirements of 300.11, which prescribes how to secure them in place.
  • Ventilation in the underfloor area is for the ITE room only, and the ventilation system is arranged so that upon the detection of fire (or products of combustion), the circulation of air will cease.
  • Openings in the raised floors protect the cables against abrasions.
  • Cables, other than branch circuit conductors covered in (D)(2) and those complying with (a), (b) and (c) below, are listed as Type DP cable suitable for use under raised floors of an information technology equipment room.
(a) Interconnecting cables enclosed in a raceway.
(b) Interconnecting cables listed with equipment manufactured prior to July 1, 1994, being installed with that equipment.
(c) Signal or communication cables of the following types: Type TC (Article 336); Types CL2 CL3, and PLTC (Article 725Types NPLF and FPL (Article 760); Types OFC and OFN (Article 770); Types CM and MP (Article 800); Type ); CATV (Article 820). See Figure 645-1 un645-01 645-05D5c.cdr.
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Securing in place

Some people get confused as to whether they must secure wiring in place in an ITE room or not. You must securely fasten branch circuit supply conductors in place, per the requirements of 300.11 [645.5(D)(2)]. However, you don’t need to apply these requirements to power cables or communications cables. Other items you can exclude from these requirements are interconnecting cables and associated boxes, connectors, plug, and receptacles listed as part of ITE. See Figure 645-2 un645-02 645-05E.cdr.

Keep in mind, we are talking about what goes on inside the ITE room. If cables extend beyond that room, you must install them per the applicable Article. For example:

  • Communications circuits-Article 800
  • Fiber optic circuits-Article 770
  • Fire alarm systems-Article 760
  • Signaling circuits-Article 725

[645.7] When wiring systems penetrate the fire-resistant room boundary, you must seal them per the requirements of 300.21.

Disconnecting Means

[645.10] You must provide a disconnecting means to disconnect power to all equipment in the ITE room and dedicated HVAC systems serving the room. Think of this. Firefighters arrive at an ITE room. How can they shut off everything in it, quickly?

The NEC answers that problem by requiring the “control” for the disconnecting means be grouped, identified and located 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 provide a button as a means to disconnect power, pushing the button “in” must disconnect the power. One way to provide the “control” for the disconnect is to use a normally open momentary pushbutton at all exiting doors. This is why you will often see a red E-stop, or Emergency Stop Switch, outside an ITE room. The E-stop controls a shunt-trip circuit breaker or, via some circuitry, multiple shunt-trip breakers.


This is an area where many people create conditions hazardous to equipment and people. It is typical for installation manuals to be well-intentioned, but wrong. Don’t choose between following safe grounding practices and following an incorrect manual. Contact the manufacturer and explain why you must follow Article 250. Document the discussion. If you are a contractor, work with your customer on this issue. In a negligence trial, Article 250 will carry more weight than a manufacturer’s manual. For one thing, Article 250 is backed by IEEE-142 and other industry standards, as well as basic engineering concepts like Ohm’s Law and Kirchoff’s Law. A manufacturer’s manual that conflicts with Article 250 also conflicts with industry standards and engineering fundamentals.

[645.15] You must ground metal parts of an information technology system per the requirements of Article 250. This does not mean driving a ground rod and calling the system grounded. You need to bond your ITE grounding bus to the main grounding system. Where signal reference structures are installed, you must bond them to the equipment grounding system provided for the ITE. You can’t consider power derived from listed ITE as separately derived for applying 250.20(D).

Remember, electricity is always trying to get back to the source, not the earth. If you use earth as your bonding jumper, the impedance path to actual ground may be several million or billion ohms higher than it should be. This means noise and undesirable current will seek other paths, per Kirchoff’s Law. Those paths include the backplanes of circuit cards in the ITE itself. Undesired current will circulate in equipment neutrals rather than dissipate to ground. If you fail to bond back to the source, you also create a shock hazard.

What about isolated grounding receptacles? Most people misapply these, and thus add more noise to the system while leaving a shock hazard for end-users. See 250.146(D) and 406.2(D) for the requirements for isolated grounding-type receptacles.

You can sum up Article 645 into a few key concepts. First, it pertains only to rooms that meet certain requirements, regardless of what equipment they contain. Second, you must fasten branch circuit power conductors securely in place. You don’t need to secure other cabling in place, but you must ensure it is protected from damage. Third, you must meet disconnect requirements that allow for a quick shut-off from the exit. The last concept to know is that grounding is grounding-apply Article 250.

The number of rooms covered by Article 645 will continue to grow. Your chances of applying Article 645 in the field are greater now than they ever were, and will increase with time.

Copyright © 2002 Mike Holt Enterprises,Inc.
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