NEC 645 Might Not be for You
First of all, let us present a few important facts about Article 645 of the National Electrical Code: it is titled "Information Technology Equipment," but it does not apply to most IT equipment, and devices listed as IT equipment do not have to be installed in IT equipment rooms.
The reason that we make this last point is because most people associate IT equipment with computer rooms and data centers. The truth is that most IT equipment is not used in such locations. For example, any desktop computer, fax machine or printer is a piece of IT equipment, but isn't only found in computer rooms—and isn't directly covered by the NEC.
But when a room is full of electronic equipment racks and dedicated cooling equipment, most people call it a data center or a computer room. They then look to the NEC and assume that the room must comply with Article 645. There are, however, some important facts to keep in mind. First, only chapters 1 through 4 of the NEC are mandatory. Secondly, chapters 5, 6 and 7 apply to special occupancies, special equipment or other special conditions. These chapters describe applications in which certain additional requirements are necessary or in which certain exceptions can be made to the requirements of the previous four chapters.
Finally, if you choose to install your equipment in accordance with Chapters 1%%MDASSML%%4 and do not need the leniencies granted by Article 645, then you do not have to meet all of the additional requirements spelled out in Article 645. Compliance with Article 645 is optional .
There are two main leniencies granted by Article 645. First, non-plenum-rated cables are permitted below a raised floor. And second, listed IT equipment cables, boxes and the like are not required to be secured in place.
Other minor leniencies are also possible in a room designed to comply with Article 645. If the installation does not benefit from these more relaxed rules, then there is no reason to comply with the additional requirements.
A raised floor makes a convenient place to run chilled water piping and long lengths of power and data cables. Since IT equipment is constantly being installed, removed, relocated or reconnected, it is nice to have the easy access that is not possible when conduits are mounted in floors and walls. But because the raised floor is sometimes used as an air plenum, it was necessary for the NFPA to write some special requirements for circuitry/cable to be put there. Today it is common practice to run power and data cables both below the raised floor or in overhead cable trays, although clearly overhead cable tray reduces the need for raised floor and decreases the obstructions to the airflow where raised floor exists.
If the leniencies associated with a raised floor are not needed, then compliance with Article 645 might not be needed either.
Emergency power off (EPO) stations are not mandatory for data centers. Paragraph 645.10 requires "a means" to " disconnect power to all electronic equipment in the information technology equipment room. There shall also be a similar means to disconnect the power to all dedicated HVAC systems serving the room and cause all required fire/smoke dampers to close. The control for these disconnecting means shall be ... readily accessible at the principal exit doors ."
IT managers dread EPO station devices. They see them as single points of failure forced upon their mission-critical networks. No such requirement exists for IT equipment installed in rooms compliant with chapters 1 through 4 of the NEC.
If a designer chooses to comply with Article 645, there is past precedent for not requiring EPO stations in some installations. Paragraph 645.10 grants exceptions to installations that qualify under the provisions of Article 685, "Integrated Electrical Systems."
NEC Article 685 is used when "an orderly shutdown is necessary to ensure safe operation. There have also been instances in which the authority having jurisdiction (AHJ) has allowed an exemption based upon severe financial consequences or business disruption, but only when satisfied that an alternate method could ensure that equivalent objectives could be achieved, per NEC 90.4.
Because power and HVAC are the lifeblood of all IT installations, very careful consideration should be given to whether to comply with the additional requirements of Article 645. The prerequisites to these leniencies are found in 645.4 (NEC-2005), which states that the article shall apply, provided all of the following conditions are met: If you are unwilling or unable to follow the prerequisites in 645, then the leniencies found in the remainder of 645 cannot be used. Thus it is an optional code article. You can choose to comply with the prerequisites or not, depending on your application.
In addition to the above requirements for a disconnecting means EPO, other special requirements of Article 645 include:
Special HVAC air transport restrictions;
Equipment that can be installed in the room must be listed as information technology equipment;
personnel entry limitations;
fire resistant-rated walls, floors and ceilings, and automatic smoke dampers;
where a raised floor is used, install smoke detectors below the floor and, upon alarm, automatically cease airflow below the raised floor.
Best practices, criticality of the mission and safety must all be weighed and balanced. NEC Article 645 makes several references in fine print notes to another document, NFPA 75, "Standard for the Protection of Information Technology Equipment," which is another useful resource for designing IT environments, and which also incorporates NEC Article 645 in its entirety. NFPA 75 is a standard, not a code, and is not adopted by most jurisdictions and cannot be enforced by the jurisdiction.
Before designing a room to comply with NEC Article 645, assess the risks and benefits that the article provides and review your plans with the local AHJ. Article 645 might not be right for the project.
Things to Know About Article 645
There are some important facts to keep in mind about the National Electrical Code, Article 645, which covers information technology equipment:
Only chapters 1 through 4 of the NEC are mandatory.
Chapters 5, 6, and 7 apply to special occupancies, special equipment or other special conditions. These chapters describe applications in which certain additional requirements are necessary or in which certain exceptions can be made to the requirements of the previous four chapters.
If you choose to install your equipment in accordance with Chapters 1%%MDASSML%%4 and do not need the leniencies granted by Article 645 , then you do not have to meet all of the additional requirements spelled out in Article 645. Compliance with Article 645 is optional .