Article 645 - Code Basics
by Mike Holt for EC&M Magazine
What you dont 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 doesnt apply. Thus, the first thing you need to know is what an ITE room is.
[645.2] An ITE room meets the following conditions:
If the room doesnt 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.
 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:
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:
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 dont 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:
[645.7] When wiring systems penetrate the fire-resistant room boundary, you must seal them per the requirements of 300.21.
[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. Dont 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 manufacturers manual. For one thing, Article 250 is backed by IEEE-142 and other industry standards, as well as basic engineering concepts like Ohms Law and Kirchoffs Law. A manufacturers 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 cant 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 Kirchoffs 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 dont 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.