Afew years ago, Gary Jones, chair of the Texas Chapter and now an instructor with the International Association of Electrical Inspectors (IAEI) said, “My guys need to hear…again that just because a room is full of computer equipment doesn’t mean that the room is automatically covered by Article 645 (of the National Electric Code [NEC]). Many contractors, engineers, and users need to understand that, too.”
The confusion existed because chapters one to four of the NEC are mandatory, but chapters five to seven permit alternative wiring methods for special occupancies. Article 645 allows leniencies for power cables distributed under raised floors that would not normally be allowed in a plenum but only when certain conditions are met.
The revised scope of Article 645 of NEC-2011 makes clear that using Article 645 is “permitted” but not mandatory. Complying with the conditions of Article 645 is probably not necessary in data centers that that use overhead cabling or are not on raised floors. This small change is just one of many that were part of a complete revision of Article 645. Table 1 gives a brief summary of these changes.
These changes to Article 645 include three significant revisions and several definitions and clarifications that have been added or revised. Article 645 now distinguishes between telecommunications and information technology equipment in the same room and alternative methods of disconnecting means are introduced.
In addition, NEC Article 645 references another document, National Fire Protection Agency (NFPA) 75 Standard for the Protection of Information Technology Equipment, four times in its “informational notes” (known in previous editions of the NEC as “fine print notes”). NFPA 75 addresses room construction for fire safety. Compliance with NFPA 75 is not mandatory in the NEC but is strongly implied. NFPA 75 likewise references NEC Article 645.