Article 800 - Communications Circuits
by Mike Holt for EC&M Magazine
Dont let misunderstandings of Article 800 hang you up.
The telephone company provides the cable to a terminal box at the building and installs a ground wire to the grounding electrode system [90.2(B)(4) and 800.40]. The dividing line between the telephone company and premise phone wiring is the primary protector unit (see Figure 800-2 un800-02 800-01 02.cdr). Wiring from that point into the premises for the telephones is where Article 800 applies (see Figure 800-1 un800-01 800-01 01.cdr). It also applies to wiring for other communications purposes, such as local area networks (LANs) and alarm systems connected to central stations.
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Of the eight definitions in 800.2, Point of Entrance may be the most important-it applies to cable grounding [800.33] and determining the length of unlisted cable inside a building [800.50, Exception No. 3]. The point of entrance is where the cable emerges from an external wall or a concrete floor slab, or from a rigid metal conduit or intermediate metal conduit grounded to an electrode per 800.40(B). See Figure 800-3 un800-03 800-02.cdr.
One aspect of good workmanship is routing cables so the suspended-ceiling panels dont interfere with access to electrical equipment (see Figure 800-4 un800-04 800-05.cdr). Secure cables to structural components by straps, staples, hangers, or similar fittings designed and installed so as not to damage the cable (see Figure 800-5 un800-05 800-06 01.cdr).
Support cables exposed on the surface of ceilings and sidewalls-attach them to the structural components of the building in such a manner that normal building use wont damage them. If you install cables near framing members, protect them against physical damage from penetration by screws or nails by 1 1/4 in. separation from the face of the framing member, or by a suitable metal plate per 300.4(D). See Figure 800-6 un800-06 800-06 02 300-04D.cdr.
If you install cables in hazardous (classified) locations, do so per Chapter 5 requirements. Where practicable, leave a separation of at least 6 ft between communications wires and cables on buildings and lightning conductors (see Figure 800-7 un800-07 800-13.cdr).
You must provide listed protective devices if your installation meets any of the conditions listed in 800.30(A)-for example, your installation has lightning exposure. Be sure to install these per 110.3. You can use fuseless primary protectors under any of five conditions listed in 800.30(A)(1). Otherwise, you must provide fused primary protectors.
Locate fused primary protectors in, on, or immediately adjacent to the building being served and as close as you can to the point of entrance. Dont locate them in hazardous areas, except as permitted by 501.14, 502.14, and 503.12.
[800.33] You must ground the metallic sheath of telephone cable and primary protectors as close as practicable to the point of entrance of the phone cable to the building or structure (see Figure 800-8 un800-08 800-33.cdr). What grounding methods should you use? Lets take a look at 800.40. Keep the following points in mind:
The utilities were using 5 foot ground rods before the NEC began to cover communications systems. There is nothing prohibiting you from using a longer rod. You must connect the grounding conductor from that rod to the nearest of nine locations listed in 800.40(B). If the building or structure has a grounding means, Figure 800-10 un800-10 800-40B1.cdr applies. The last FPN in 800.40 brings out an important concept: bond together all separate electrodes to limit potential differences between them and between their associated wiring systems (see Figure 800-14 un800-14 800-40D 02 .cdr).
[800.48] Raceways are optional for communications circuits. You can install communications cables in any of the Chapter 3 raceways, if you do so per the appropriate article for a given raceway. Exception: Conduit fill restrictions do not apply to communications cables and conductors installed in a raceway.
You can also install communications cable installed in listed communications raceways per 800.51(J), (K), or (L). Communications raceways are similar in nature to electrical nonmetallic tubing (ENT)-apply 362.24 through 362.56.
The recommendations of the BICSI Cabling Installation Manual include specific pulling tension on the cables. Since most installers have no idea how to limit the pulling tension on signal or communication cables, the generally accepted practice is to size the raceway so the cables do not exceed the percentage fill listed in Chapter 9, Table 1.
Listing and Markings
Use only communications cables listed as being suitable for the purpose, and marked in accordance with Table 800.50-and install them per 800.52. There are exceptions to this. For example, listing and marking are not required where the cable enters the building from the outside and runs in rigid metal conduit or intermediate metal conduit, and when the raceway is grounded to an electrode per 800.40(B). If installing in plenums, risers, or other environmental air spaces, review 800.51 carefully.
Dont mark the 300V ratings on these cables-misinterpretation can suggest the cables may be suitable for Class 1, or electric light and power applications. For specific applications of cable types and what listing is appropriate, see 800.53.
Never attach communications cable to, or support it with, raceway [300.1] or the power service mast [230.28]. Support via cable tie to conduit is not an acceptable method.
[800.52] Communications cables can be in the same raceway or enclosure with cables of any of the following (see Figure 800-19 un800-19 800-52A1a1.cdr):
Communications cables cannot be in the same cable with Class 1 circuits. Class 2 and Class 3 circuit conductors can be in the same cable with communications circuits, if the Class 2 and Class 3 circuits are contained in listed communications cable or multipurpose cable (see Figure 800-20 un800-20 800-52A1b 725-56D1.cdr).
You cannot run communications conductors in any raceway, compartment, outlet box, junction box or similar fitting with conductors of electric light, power or Class 1 circuits. Of course, there are exceptions:
In other applications, you must separate communications conductors by at least 2 in. from any electric light, power or Class 1 circuit conductors-unless you install those electric light, power or Class 1 circuit conductors per a Chapter 3 wiring method (raceway, metallic or nonmetallic sheath, or UF cable). (See Figure 800-21 un800-21 800-52A2x1.cdr).
When you install communications wiring and equipment in hollow spaces, vertical shafts, ventilation or air-handling ducts, do so in a way that does not substantially increase the possible spread of fire or products of combustion. Use approved firestops for openings made in fire-rated walls, floors and ceilings (see Figure 800-22 un800-22 800-52B 01 300-21.cdr). If theres any abandoned cable, remove the accessible portions (see Figure 800-23 un800-23 800-52B 02.cdr) to limit the spread of fire or products of combustion within a building. This rule does not require the removal of concealed cables.
Article 800 can be a bit dizzying, if you try to memorize all of its listing requirements and other details. These things, important as they are, primarily support two concepts. One of those is that you must maintain firestop integrity. The other is you must maintain separation from higher energy levels that require more stringent wiring methods and protection. If you keep these concepts in mind as you work with Article 800, youll be able to ring up one job after another with no callbacks for code violations.
Copyright © 2002 Mike Holt Enterprises,Inc.