Don’t get twisted around when installing communication circuts
Because Art. 800 has its roots in telephone technology, it addresses telephone and related systems that use twisted-pair wiring. The telephone utility typically provides the twisted-pair cable to a terminal board. This board usually is part of an assembly referred to as the network interface device (NID). Normally, you will find the NID at the “point of entrance” (Sidebar below). Wiring from that point forward falls within the scope of Art. 800.
Cable installation. The NEC requires installation in a “neat and workmanlike manner” [800.24], but doesn't explicitly define the meaning of that. However:
800.21 requires anyone installing cables above a suspended ceiling to route them so that someone can remove the panels for access to electrical equipment.
800.24 provides support and protection requirements, part of which also are found in 300.4(D).
The fine print note (FPN) following 800.24 refers to ANSI/NECA/BICSI 568, “Standard for Installing Commercial Building Telecommunications Cabling.”
800.3(C) requires you to use 300.21 for fire-stopping requirements if you penetrate fire-resistance rated walls, partitions, floors, or ceilings.
All of this helps us understand the meaning of “neat and workmanlike,” as do standard trade practices and common sense. Attention to detail is part of good workmanship, and a few strategically placed supports can work wonders — don't shy away from using them.
Abandoned cables. You must remove the accessible portion of communications cable that doesn't terminate at equipment and isn't identified for future use with a tag [800.2]. This requirement doesn't apply to cables that are installed inside of raceways (Art. 100 says they are “concealed”).
The main reason this requirement made it into the NEC is because it limits the amount of combustible items in a building, and therefore limits the possible spread of fire or products of combustion.
Conductor clearances. Overhead communications cables must not be less than 10 feet above swimming and wading pools, diving structures and observation stands, and towers or platforms [680.8(B)]. Other overhead conductor requirements are provided in 800.44.
Underground communications wires and cables in a handhole or manhole must be separated from exposed electric light, power, Class 1, and nonpower-limited fire alarm circuit conductors by a suitable barrier [800.47]. Where practicable, maintain a separation not less than 6 feet between communications wiring and lightning protection conductors [800.53].
Protection. A listed primary protector is required for each communications circuit [800.90]. Locate it as close as practicable to the point of entrance [800.90(B)]. Keeping the shortest practicable distance between the primary protector location and the primary protector grounding conductor [800.100(A)(4)] reduces differences in potential between communications circuits and other metallic systems — very important during lightning events.
Primary protectors provide protection against overvoltage and overcurrent conditions that occur due to contact between outside communication conductors and power sources outside of the building. Thus, they allow for safe direct connection of internal power limited circuits and equipment to conductors that originate outside of the building.
Grounding methods. The metallic sheath of communications cable must be grounded (or interrupted by an insulating joint) as close as practicable to the point of entrance. Follow the requirements of 800.100. The grounding conductor must be:
Insulated and listed as suitable for the purpose.
Copper or other corrosion-resistant conductive material.
Not smaller than 14 AWG.
As short as practicable. In one- and two-family dwellings, it can't exceed 20 feet.
Run in as straight a line as practicable.
Guarded from physical damage. Where run in a metal raceway, bond each end of the raceway to the grounding conductor.
In a structure with a grounding means, the grounding conductor must terminate to the nearest accessible:
Grounding electrode system [250.50].
Interior metal water piping system, within 5 feet from its point of entrance [250.52(A)(1)].
Accessible service bonding means [250.94].
Metallic service raceway.
Service equipment enclosure.
Grounding electrode conductor or the grounding electrode conductor metal enclosure.
In a structure without a grounding means, install a ground rod not less than 5 feet long and ½ inch in diameter. Then bond the grounding conductor to it [800.100(B)(2)(2)] (Fig. 1), using a minimum 6 AWG conductor [800.100(D)].
Meeting 800.133 requirements. Don't let the fact that there are eight exceptions and one FPN in 800.133 intimidate you. The first three exceptions apply to conductors in raceways, boxes, and cables. The next two apply to separation from nonpower-limited fire alarm circuits, and the last applies to support of aerial conductor spans. The FPN applies to sprinklers in concealed spaces. Five key requirements are:
If you install communications cables in a Chapter 3 raceway, the raceway must comply with the Chapter 3 wiring method installation requirements [800.110].
If you install communications cables in a nonmetallic raceway listed for communications cables, the raceway must comply with 800.182 and must be installed per 362.24 through 362.56.
Communications wires and cables installed within buildings must be listed, but the cable voltage rating must not be marked on the cable [800.113]. Voltage markings on cables may be misinterpreted to suggest that the cables may be suitable for Class 1 or electric light and power applications [800.113 FPN].
Communications circuits must maintain 2 inches of separation from electric light, power, Class 1, or nonpower-limited fire alarm circuit conductors [800.133(A)(2)].
Communications cables must not be supported by a raceway [800.133(C)]. They also can't be supported by or attached to the power service mast [230.28].
Other requirements for cables within buildings. Communications cables can be in the same raceway or enclosure as jacketed cables of any of the following:
Class 2 & Class 3 circuits [Art. 725].
Power-limited fire alarm circuits [Art. 760].
Optical fiber cables [Art. 770].
Coaxial circuits [Art. 820].
Communications conductors must not be run in the same cable with Class 1 conductors. They can be within the same cable with Class 2 or Class 3 conductors, if the cables are installed per Art. 800 [800.133(A)(1)(b), 725.56(D)(1)] (Fig. 2).
Type CMP, CMR, CMG, and CM communications cables [800.179], and listed communications raceways [800.182], can be installed in cable trays [800.154(D), 392.3(A)].
Ducts and plenums. Communications cables must not be installed in ducts that transport dust, loose stock, or vapors [300.22(A)].
Only where necessary for the direct action upon, or sensing of, the contained air, communications cables can be installed in ducts or plenums if they are installed in electrical metallic tubing, intermediate metal conduit, or rigid metal conduit per 300.22(B).
Plenum-rated Type CMP cables [800.179(A)] can be installed above a suspended ceiling or below a raised floor that is used for environmental air [800.3(D), 300.22(C)]. Plenum-rated communications raceways [800.182] are permitted above a suspended ceiling or below a raised floor used for environmental air, but only if the raceway contains Type CMP plenum-rated cables (Fig. 3).
Risers. Cables installed in vertical runs penetrating more than one floor must be Type CMR [800.179(B)]. Floor penetrations requiring Type CMR must contain only cables suitable for riser or plenum use. Where installed in risers, communications raceways with Type CMR and CMP cables are permitted. Type CM cables must be encased in a metal raceway or located in a fireproof shaft having a firestop at each floor.
You can install Type CM and CMX cables for all applications in one- and two-family dwellings. Plenum- and riser-rated communications cables are not required in one- or two-family dwellings.
“Article 800 Tips” on page 52 highlights some key points for proper application of Art. 800. How can you keep track of all the details? One trick is to remember these three principles of Art. 800:
Keep these communications circuits separate from other circuits, such as those used for power and lighting.
The need for proper bonding applies to all circuits.
Plan and execute the job with maintainability in mind.
If you remember these principles, the details of proper application will always make sense.
Don't attach incoming cables to the service-entrance power mast.
Ground the primary protector as close as practicable to the point of entrance, keeping the grounding (earthing) conductor for the primary protector as straight and as short as possible.
If you locate cables above a suspended ceiling, route and support them to allow access via ceiling panel removal, and be sure to identify when to use plenum-rated cables or raceways.
Keep communications cables separated from lightning protection circuits.
If you install cables in a Chapter 3 raceway, you must conform to the NEC requirements for the raceway system.
Special labeling and marking provisions apply — follow them carefully.
Be sure to use the right cable type. Nothing can ruin your day faster than installing CM cables when you should have installed CMR or CMP.
The “point of entrance” is the point at which the cable enters the structure [800.2]. That may be an external wall or a concrete floor. It might also be rigid metal conduit or intermediate metal conduit that is grounded (bonded) to an electrode per 800.100 (Figure).
You have to identify this point for two reasons:
To properly locate the primary protector [800.90(B)].
To know where to ground (bond) the communications cable [800.93] to the grounding system.