Clarifying NEC Articles 725 and 800

07/17/2013


If not in Article 800, then where?

Figure 2: This shows the relationship between Article 645 and Article 725. Courtesy: CH2M HILLThe section of the NEC that applies to the cable illustrated in Figure 1 is covered by Article 725. This may not be immediately obvious by reading the first couple of pages of this Article. It is easier to come to this determination by first reading Article 645: Information Technology Equipment, which describes the code requirements for the cabling of computer systems (defined by the NFPA as information technology equipment). The cabling for our illustration in Figure 1 is for the data transport of the computing system. It is within section 645.3, Other Articles, in paragraph (D) that the NEC defines the electrical classification of a data circuit. Figure 2 shows the linkage between the sections within Article 645 to the circuit types defined in 725.

From the references in Figure 2, you would be correct in describing the network cable in our example as a “signaling circuit,” a “Class 2 or Class 3 circuit,” or a “limited-power circuit.” (Please note that nowhere is this defined as a low-voltage circuit. The NEC Handbook uses this description, but it is not in the text of the NEC itself.) When working with the NEC, my preference is to refer to a network cable as a limited-power circuit or just as a Class 2 or 3 circuit. The NEC recognizes a difference between a Class 2 circuit and a Class 3 circuit as a Class 2 circuit being intrinsically safe. A Class 3 circuit has a protection device incorporated into the power supply to make it intrinsically safe. However, for Class 2 and Class 3 circuits, the same sections of Article 725 apply. In the small power supplies I have seen for POE devices, media converters, powered telephone sets, and other small network devices, they have all been listed as Class 2 power supplies. The larger network equipment, such as multi-card chassis, have much larger power supplies and probably have some form of internal protection circuiting to make them intrinsically safe, although I have never seen them listed as a Class 3 device. Therefore, I often refer these as just limited-power or Class 2 circuits.

There are provisions in sections 645.3(D) and 725.139(D) for a Class 2 circuit to be considered a communication circuit and therefore be installed per Article 800. This is in the case where the Class 2 (network) circuit shares the same cable with the communications circuit. This is often misinterpreted to mean that when Class 2 cables and communication cables are combined, such as in a tray or conduit, all the cables can be considered communications cables and would be installed per Article 800. This is not what the code says. It states in both of the sections referenced that when the two circuit types share the same cable, they can be combined. Or in other words, both circuits have to be within the same cable jacket. The sections are written to say the two different types of circuits have to be within the same cable.

During the early days of 10Base-T Ethernet, you would often see where two pairs of a four-pair Category 3 cable were used for the Ethernet circuit and one pair of the same cable was used for telephone. The Ethernet circuit would be covered under Article 725, and if the telephone phone circuit was an extension of a telephone line from the telephone company, it would be covered under Article 800. Sections 645.3(D) and 725.139(D) allowed this convergence of technologies to be covered under Article 800. Nowadays, a circuit of this configuration is rare.

More on Article 725  

Figure 3: Even though a network cable (shown here) does not present harmful voltages, there are a variety of safety issues to be considered. Courtesy: CH2M HILLAdditional information on the intent of Article 725 can be found in the NEC Handbook in the editors’ text that describes the scope of Article 725. The NEC Handbook states:

The installation requirements for the low-voltage wiring of information technology equipment (electronic data processing and computer equipment) located within the confines of a room that is constructed according to the requirements of NFPA 75, Standard for the Protection of Information Technology Equipment, are not covered by Article 725. Low-voltage wiring within these specially constructed rooms is covered in Article 645.

Also, if listed computer equipment is interconnected and all the interconnected equipment is in close proximity, the wiring is considered an integral part of the equipment and therefore not subject to the requirements of Article 725. If the wiring leaves the group of equipment to connect to other devices in the same room or elsewhere in the building, the wiring is considered ‘‘wiring within buildings’’ and is subject to the requirements of Article 725.

The last sentence of this quote from the Handbook addresses the cabling in our example. The editors’ text from Article 800 of the NEC Handbook complements this. It states:

Section 90.3, covering the structure of the NEC, specifies that Chapter 8 (comprised of Articles 800, 810, 820, and 830) covers communications systems and is not subject to the requirements of Chapters 1 through 7, other than where a requirement from these chapters is specifically cited by a Chapter 8 requirement. As an example, 800.24 references 300.4(D) and 300.11, 800.44(A)(3) references 225.14(D), and 800.90(C) references 500.5.

Although information technology equipment systems are often used for or with communications systems, Article 800 does not cover wiring of this equipment. Instead, Article 645 provides requirements for wiring contained solely within an information technology equipment (computer) room. (See 645.4 for a description of the type of information technology equipment room to which Article 645 applies.) Article 725 provides requirements for wiring that extends beyond a computer room and also covers wiring of local area networks within buildings. Article 760 covers wiring requirements for fire alarm systems.

The NEC Handbook goes on to say that when telephone system wiring is also used to transmit data, it is covered by Article 800. Examples of this would be a fax or modem line extending into a building by a telephone service provider. The Handbook also states “communications equipment (see Article 100 for definition), such as the private automatic branch exchange shown in Exhibit 800.1, and all of the premises wiring for a communications circuit (see 800.2 for definition), are subject to the requirements of Article 800.” One may conclude from this sentence in the Handbook, that “all the premise wiring” from a telephone switch is covered under Article 800. However, keep in mind it is still referring to the definitions for a “communications circuit,” and that is a circuit that is being extended by a communication utility.

Figure 4: This rendering is of a server row consolidation point, face view. Courtesy: CH2M HILLFor a privately owned telephone switch, the cabling extending from the switch to the telephone outlets may be covered under Article 725. Article 725.121(A)(4) identifies the power sources for Class 2 and Class 3 circuits as “listed information technology (computer) equipment limited-power circuits.” The code then provides an informational note referring to UL 60950-1-2003, Standard for Safety of Information Technology Equipment. This UL document describes the requirements for a piece of equipment to be considered “information technology equipment.” With UL 60950-1-2003 there is a variety of equipment listed that includes data switches, routers, and telephone equipment such as a private branch exchange or telephone switch.

Therefore, if a privately owned telephone switch is UL 60950-1-2003 compliant, the cabling from it can be covered under Article 725. What is important to note here is that NEC 725.121(A)(4) provides a reference to the UL standard identifying information technology equipment and the UL standard goes on to identify a PBX as a type of information technology equipment.

Don’t be fooled by the cable markings on commonly seen on network and telephone cabling. Although we see CM, CMR, and CMP listed cables used for network cables, that doesn’t mean these are Article 800 circuits. Article 725 allows for the substation of CM, CMR, and CMP cables for the Class 2 and Class 3 listed cables.

A little grey in the interpretation

The code is a complex document that has been revised repeatedly. Some interpretations seem crystal clear while other interpretations are still in the grey. From the code interpretations listed above, I would argue that clearly Ethernet and similar network copper cabling is covered by Article 725. Communication circuits, as defined by the NEC, are circuits that extend from a utility (telephone company) to some type of terminal equipment (telephone, fax, or answering machine). I believe these two interpretations are very clear.

The grey area is the cabling from the PBX to the telephones. The NEC Handbook states, “communication equipment, such as a private automatic branch exchange shown in Exhibit 800.1, and all of the premises wiring for a communications circuit (see 800.2 for definition), are subject to the requirements of Article 800”—even though the UL Standard 60950-1 referenced from Article 725 lists a PBX as information technology equipment. For telephone cables from a PBX, it appears either 800 or 725 could be applied. It turns out that the code requirements in applying 725 or 800 are so similar that installing a cable compliant to Article 725 is also compliant for Article 800.

Telephone circuits that are VoIP circuits are no different than other local area network (LAN) circuits and would be covered under Article 725. With the technology shift to more companies installing VoIP systems for telephony applications, the role of Article 800 inside a building is diminishing. As more and more services are transported over Ethernet copper circuits, it is important for us to know that we need to apply Article 725 to their installation.


Timothy Kuhlman is an electrical engineer with CH2M Hill, where he is a technologist in the industrial and advanced technologies business unit. He has 23 years of experience in the field of telecommunication system design and is registered as professional engineer in 15 states. He is a member emeritus of the Consulting-Specifying Engineer editorial advisory board.


Definitions 

CM, CMR, and CMP: NEC cable listing designation for communication cables per article 800.110. CM: general purpose communications; CMR: riser communications; CMP: plenum communications. 

General purpose cable listings: CL2 or CL3. Per substitution table 725.154(G) cable types CM allowed. 

Plenum cable listings: CL2P or CL3P. Per substitution table 725.154(G) cable types CMP allowed. 

Riser cable listings: CL2R or CL3R. Per substitution table 725.154(G) cable types CMR allowed.

RoIP: Radio over Internet protocol (IP). Often a traditional FM channelized or trunked system integrated using Internet protocols.

SoIP: Security over Internet protocol (IP). A security system using Ethernet or IP as its transport protocol. 

VoIP: Voice over Internet protocol (IP).


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