What the NEC says about data/comm cables in computer rooms

Changes to Article 645 include a definition of IT equipment that distinguishes it from communications equipment, and wording about the Article’s voluntary nature.

From the February, 2012 Issue of Cabling Installation & Maintenance Magazine

Changes to Article 645 include a definition of IT equipment that distinguishes it from communications equipment, and wording about the Article’s voluntary nature.

By Stanley Kaufman, Cablesafe inc.

The National Electrical Code is published by the National Fire Protection Association with revisions on a three-year schedule. The 2011 NEC, which replaces the 2008 NEC, was released by NFPA in August 2010. There were many changes of interest to manufacturers, installers and users of communications cable and connectivity products. (NFPA 70, National Fire Protection Association, National Electrical Code and NEC are registered trademarks of the National Fire Protection Association.)

This is the eighth article in a series of nine articles, contributed on behalf of the Communications Cable and Connectivity Association (CCCA; www.cccassoc.org), concerning those relevant changes in the NEC.

The seven preceding articles covered:

  • Introduction to the NEC, its scope and organization
  • Changes in types and installation rules for data/comm raceways
  • Changes in the permitted applications of data/comm cables in air handling spaces
  • Changes in the wiring rules for data/comm cables in riser applications
  • Introduction of cable routing assemblies
  • Data/comm cable applications
  • Data/comm cable installation requirements

This article deals with the changes made to NEC Article 645 Information Technology Equipment that clarify or change the applications of the article to data/comm wiring. This article does not address the power wiring requirements in Article 645.

Article 645

NEC Article 645, Information Technology Equipment, is intended to apply to the installation of information technology equipment and wiring in a computer room that complies with NFPA 75, Standard for the Protection of Information Technology Equipment. Because the NEC Style Manual prohibits mandatory references to other standards (section 4.2), Article 645 takes an alternate approach of listing a series of conditions that must be satisfied in order to use the article. These conditions include many of the most important fire-protection requirements in NFPA 75.

Unfortunately, the voluntary nature of Article 645 is not clearly stated in the 2008 NEC. In fact, Section 645.4 states, “This article shall apply, provided all of the following conditions are met:” It then lists the conditions.

That inarticulate wording has been fixed in the 2011 NEC. Section 645.4 states, “This article shall be permitted to provide alternate wiring methods to the provisions of Chapters 1 through 4 for power wiring, 725.154 for signal wiring, and 770.113(C) and Table 770.154(a) for optical fiber cabling when all of the following conditions are met:”

Data/comm wiring in a computer room

While the scope of Article 645 states that it applies to interconnecting wiring in an information technology equipment room, virtually all the data/comm wiring requirements deal with wiring in the underfloor area. That area in a computer room is typically used to supply cooling air and is therefore a “raised floor plenum” (NFPA 90A terminology) or an “other space used for environmental air” (NEC section 300.22 terminology).

Article 645 is permitted to apply if six conditions are met, including the provision of disconnecting means for shutting down the equipment in an emergency. A typical disconnecting means is a switch with a big red button at the door. Article 645 has relaxed wiring provisions for data/comm wiring in the raised floor plenum. Plenum cabling is not required where there is a remote disconnecting means, typically at the exit door.

Data centers meeting additional conditions (beyond the six basic conditions for permission to apply to use Article 645), are permitted to be designated as critical operations data systems. Data/comm cables, exposed to the airflow in the raised floor plenum of a critical operations data system, are required to be listed for plenum use; Types CL2P, CL3P, OFNP, OFCP, CMP and CATVP. These data centers are not required to have remote disconnecting means.

NEC Code organization

Section 90.3, Code Arrangement, permits Chapters 5, 6 and 7 to modify the general wiring rules in Chapters 1 through 4. It also states that Chapter 8 (Communications) is not subject to the requirements of Chapters 1 through 7 except where the requirements are specifically referenced in Chapter 8.

Article 645 in the 2008 NEC has numerous references to communications cables without any correlating references in Chapter 8. Also, it does not distinguish between IT equipment and communications equipment, the former being covered by the article and the latter not covered.

Distinguishing between IT and communications equipment

A definition of communications equipment is well established in the NEC, first appearing in Article 800 in the 2005 NEC, and moved to Article 100, Definitions, in the 2008 and 2011 NEC. Article 645 in the 2011 NEC now has a definition for Information Technology Equipment. That definition is carefully crafted to distinguish IT equipment from communications equipment.

Distinguishing between IT equipment and communications equipment is necessary because the special wiring dispensations for IT equipment in Article 645 (plenum cable not required in raised floor plenum) apply only to IT equipment and not to communications equipment.

An important provision applies to class 2 circuits and communications circuits. Sections 725.193(D)(1) and 800.133(A)(1)(c) state that when a class 2 or 3 circuit and a communications circuit are in the same cable, the class 2 or 3 circuit is reclassified as a communications circuit. Data circuits are class 2 or 3 circuits [see 725.121(A)(4)]. Consequently, any cable carrying a combination of communications and data circuits must be a communications cable and comply with the provisions of Article 800, Communications Circuits.

In addition to a definition of IT equipment that correlates with the definition of communications equipment, Article 645 in the 2011 NEC now has a new section, “Other Articles,” that links Article 645 to other key articles in the Code and clarifies which requirements apply.

Relationship between 645 and Other Articles

New section 645.5 in the 2011 NEC correlates Article 645 with other articles of the code in order to minimize misinterpretations. It has subsections (A) through (G). (See the table on page 14 for a summary of the new section.) Having carefully defined IT equipment, 645.3 clarifies that Article 800 applies to communications equipment in the room and that the dispensation in 645.5(E) that permits riser and general-purpose cables to be run in the raised floor plenum does not apply to communications circuits; Type CMP is required. CATV cabling is treated in the same manner as communications cabling. Section 645.3(D), which deals with the classification of circuits, is useful when deciding whether a circuit is a data circuit or a communications circuit.

New section 645.3 leads the user to all the sections that call for firestopping; it also leads to the sections on wiring in plenums and thereby reminds the user that the dispensations in Article 645 apply to the raised floor plenum only. Article 645 does not amend the wiring rules for ceiling cavity plenums. In fact, it is prohibited from doing so because NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilation Systems, has primary responsibility for fire protection of combustibles in plenums and NFPA 90A permits alternate wiring methods for raised floor plenums but not ceiling cavity plenums in a computer room in compliance with NFPA 75.

Another section of the Code that is easily overlooked is the section requiring grounding of the conductive member of a conductive optical fiber cable. This is important because of the use of armored optical fiber cables in data centers. Section 645.3(C) requires grounding in compliance with 770.114.

The 2014 NEC

Many improvements were made to Article 645 in the 2011 NEC. Further improvements could be made in the organization of the article. The order of the sections could be reorganized to comply with section 2.1.4 of the NEC Style Manual, which permits (encourages) articles to be subdivided into logical groupings of information. Many articles in the Code start with a general section, with requirements that apply generally. Many of the general requirements in Article 645 in the 2011 NEC are at the end of the article.

Another possible improvement is to augment the wiring requirements for cabling under the room by adding wiring requirements for cabling in the room.

The deadline for proposals for the 2014 NEC was November 4, 2011.

The next article will deal with a new Article 840, which addresses premises-powered broadband installations.

Author’s disclaimer: This paper, provided by the Communications Cable and Connectivity Association (CCCA), is offered for general information and educational purposes. It is not offered, intended, nor should it be relied upon as legal advice. The paper does not set forth the views of any member or any other party, nor may it be taken as such. CCCA makes no warranty regarding the accuracy of the information provided in this paper, and expressly disclaims any implied warranties and any liability for use of the paper or reliance on views expressed in it. CCCA does not endorse, approve or certify any information set forth in this paper, nor does it guarantee the accuracy, completeness, efficacy, timeliness or correct sequencing of such information. Use of the paper and the views expressed in it is voluntary, and reliance on it should only be undertaken after an independent review of its accuracy, completeness, efficacy and timeliness, and based on the individual facts and circumstances of a user.

Stanley Kaufman, Ph.D. is principal of CableSafe Inc. and a consultant to the Communications Cable and Connectivity Association (CCCA; www.cccassoc.org). He is a member of NEC Panel 12 (responsible for Article 645) and Panel 16 (responsible for optical fiber and communications cables).

Subsection 645.3
What Does It Cover?


Spread of Fire or Products of Combustion

Refers to firestopping requirements



Refers to wiring requirements for ceiling cavity plenums



Refers to grounding requirements for conductive optical fiber cables


Electrical Classification of Data Circuits

Refers to Articles 725 and 800 for the classification of mixed data and communications cables


Fire Alarm Equipment

Article 760 covers fire alarm equipment


Communications Equipment

Refers to Article 800 for communications wiring but asserts that Article 645 covers power wiring of communications equipment in an IT room


Community Antenna Television and Radio Distribution Systems Equipment

Essentially the same as (F) but applies to Article 820

It’s 2012. How come we’re still talking about the 2011 NEC?

And how come it’s too late to make a proposal for the 2014 NEC? As Dr. Kaufman has pointed out in each of his articles, the NEC is published by the National Fire Protection Association (www.nfpa.org) on a three-year schedule. A portion of the NFPA’s website is devoted to explaining how codes and standards are developed.

It explains: “NFPA Technical Committees and Code Making Panels serve as the principal consensus bodies responsible for developing and regularly updating all NFPA codes and standards. Committees and Panels are appointed by the Standards Council and typically consist of no more than 30 voting members representing a balance of interests.

“The NFPA process encourages public participation in the development of its codes and standards,” the NFPA continues. “All NFPA codes and standards are revised and updated every three to five years in revision cycles that begin twice each year and that normally take approximately two years to complete. Each revision cycle proceeds according to a published schedule that includes final dates for all major events in the process.”

Much more detail is available at www.nfpa.org. -Ed.

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