Following these guidelines and installation practices can help keep you from getting too rough when roughing in and trimming up data cabling
Roughing in communication cables is similar to roughing in electrical cables. However, you must use extra care when installing them because communication cables have far less copper than electrical cables. This means the tensile strength of the cable is proportionally less. Of course, you must precisely follow the manufacturer's instructions to make sure you use the right connectors and fittings. There are many different types of data cabling, and their placement is crucial to the final equipment connections.
Roughing in the cables. Like power wiring, you install data cabling in two primary phases: roughing in the wiring and then trimming it later.
During the rough-in phase, make sure to put all of the cables in the proper places, and be careful not to bend too tightly, pull too hard, skin, or otherwise damage the cables during installation. At this time, consider the routing of the cables, especially if they are unshielded. You should never place unshielded copper cables too closely to sources of electromagnetism, such as motor windings, transformers, ballasts, or the like. Also, keep the locations of fire barriers of the structure in mind, and yield proper allowances when crossing them.
Because data cables are more delicate than power wiring, be sure to protect them during construction. This is critical in situations where there will be a long lag time between your cable installation work and final termination work. If the cables acquire any damage during this time, you may not know it until you get a tester on them. And like power wiring, it's important to leave enough extra cable at each outlet point. The recommended lengths are a minimum of 3 m in the telecommunications closet for both twisted-pair and fiber cable, 1 m for fiber, and 30 cm for twisted-pair cable at the outlet. (Notice when you move from power wiring to data cabling, the units of measurement switch from English to metric.) Also, remember to check your specifications on every job, as some owners may require extra cable.
In other situations, such as when you have a complete raceway system to use, there may be very little time between the cable installation and wiring of the jacks.
Trimming the cables. Trimming data cabling is pretty much the same as trimming power wiring. First, you strip the cables. Then you install the devices and plates (and so on). The difference is in the amount of required testing. When trimming power wiring, we generally test by flipping a switch or hitting the outlet with a "Wiggy." Either power is present, or it's not. Testing data cabling is not so simple. Remember, you need to test not only for the presence of the signal, but also for the quality of the signal. Plan on spending a generous amount of time testing the cables you install and documenting those test results.
Wiring layouts. In Part 2 of this series, on page 56F of the February issue, we explained topology-the patterns in which data networks connect computers. If you remember, topology decides how your cables are run. In most cases, this will be a star pattern, meaning every data outlet gets its own home run. (EIA/TIA Std. 568, Commercial Building Telecommunications Wiring Standard, recommends this configuration, which almost all new computer networks follow.)
Under this system, a Cat. 5 (or now, perhaps level 5e) cable runs from each computer station (node) to a communications closet (the communications equipment is typically in a telephone closet). This can cause space problems, especially in preexisting buildings. During your estimating and planning stages, remember the closets may be overcrowded.
At the wiring closet, your cable home runs will connect to a punch-down block. The standard method of connecting communications conductors is at a multi-terminal assembly of self-stripping, crimp connections. We call this component a punch-down block, 66 block, or 110 block. Punch-down block is the generic name, 66 blocks are for voice conductors, and 110 blocks are for data conductors.
From the punch-down block, you run short patch cables to a patch panel, and from there to a hub. A hub is an electronic device that takes the signals from each of the cables, and puts them into a backbone cable, which runs between floors of the building, and connects several hubs together. You may also hear hubs referred to as concentrators.
We use patch panels and punch-down blocks to facilitate testing and provide for additions and modifications to the cable plant (cabling system). The outlet itself is almost always one or two RJ-45 jacks you mount on a single-gang plate. (The RJ-45 is the 8-pin modular phone plug. Universally, we use it for data networks.)
Cable colors. While the color coding of data cabling is not as popular as the color code for power conductors, color codes do exist and you should follow them. Telecommunications Cabling System Administration (EIA-606) lists the colors and functions of data cabling as:
• Blue (horizontal voice cables)
• Brown (inter-building backbone cables)
• Gray (second-level backbone cables)
• Green (network connections and auxiliary circuit cables)
• Orange (telephone cable from central office or demarcation point)
• Purple (first-level backbone cables)
• Red (key-type telephone system cables)
• Silver or white (horizontal data cables; computer and PBX equipment)
• Yellow (auxiliary, maintenance, and security alarm cables)
Minimum bending radius. According to a draft version of EIA/TIA Standard 568, the minimum bend radius for UTP cable is four times outside cable diameter, or about 1 in. For multi-pair cables, the minimum bending radius is 10 times outside diameter. The minimum bend radius for Type 1A Shielded Twisted Pair (100 Mb/s STP) is 7.5 cm (3 in.) for nonplenum cable, and 15 cm (6 in.) for the stiffer plenum-rated kind.
For an optical cable not under tension, the minimum bend radius is 10 times its diameter. For cables under tension, the requirement is no less than 20 times cable diameter. The standard goes on to state that you may not bend optical cable on a radius less than 3.0 cm (1.18 in.).
A different standard, ISO DIS 11801 (a parallel standard to the one mentioned earlier), lists three different minimum bend radii for 100 ohm and 120 ohm balanced cable. For copper cables, the minimum radii for pulling during installation is eight times cable diameter, six times for riser cable, and four times cable diameter for horizontal runs. For fiber optic cables, the requirements are the same as those stated above.
Manufacturers' recommendations differ, so it is worth checking the spec sheet for each cable you plan to use.
Code requirements. National Electrical Code (NEC) Art. 800 covers communication circuits, such as telephone systems, computer networks built around telephone-style cables, and outside wiring for fire and burglar alarm systems. Generally, you must separate these circuits from power circuits and ground them. You must also provide such circuits running out of doors (even if only partially) with circuit protectors (surge or voltage suppressors).
Art. 725 of the NEC covers a few types of network cabling. Most Cat. 5 cables, however, fall under Art. 800, rather than under Art. 725. The requirements of Art. 800 cover:
Conductors entering buildings. If the same pole supports communications and power conductors, or run parallel in span, you must meet the following conditions:
1. Wherever possible, you should locate communications conductors below power conductors.
2. You shall not connect communications conductors to cross arms.
3. You must separate power service drops from communications service drops by at least 12 in.
You must meet the following clearances regarding communications conductors for above roofs:
1. Flat roofs: 8 ft.
2. Garages and other auxiliary buildings: none required.
3. Overhangs, where no more than 4 ft of communications cable will run over the area: 18 in.
4. Where the roof slope is 4 in., rise for every 12 in. horizontally: 3 ft.
You must separate underground communications conductors from power conductors in manholes or handholes by brick, concrete, or tile partitions.
Keep communications conductors at least 6 ft away from lightning protection system conductors.
Circuit protection. Protectors are surge arresters designed for the specific requirements of communications circuits. They are required for all aerial circuits not confined within a city block. Make sure you install them on all circuits with a block that could accidentally contact power circuits over 300V to ground. Also, make sure they are listed for the type of installation.
Grounding requirements. You must ground or interrupt metal sheaths of any communications cables with an insulating joint as close as practicable to the point where they enter any building (such point of entrance being the place where the communications cable emerges through an exterior wall or concrete floor slab or from a grounded rigid or intermediate metal conduit).
Grounding conductors for communications circuits must be copper or some other corrosion-resistant material, and have insulation suitable for the area where it exists.
Communications grounding conductors may be no smaller than No. 14. You must run the grounding conductor as directly as possible to the grounding electrode, and make sure it's protected if necessary. If metal raceway protects the grounding conductor, bond it to the grounding conductor on both ends.
Grounding electrodes for communications ground may be any of the following:
1. The grounding electrode of an electrical power system;
2. A grounded interior metal piping system;
3. Metal power service raceway;
4. Power service equipment enclosures; or
5. A separate grounding electrode.
If the building being served has no grounding electrode system, you can use the following as a grounding electrode:
1. Any acceptable power system grounding electrode (see Sec. 250-81);
2. A grounded metal structure; or
3. A ground rod or pipe at least 5 ft long and half-in. in diameter.
You should drive this rod into damp (if possible) earth, and keep it separate from any lightning protection system grounds or conductors.
Make connections to grounding electrodes with approved means. If the power and the communication systems use separate grounding electrodes, you should bond them together with a No. 6 copper conductor. You may bond other electrodes as well. This is not required for mobile homes.
For mobile homes, if there is no service equipment or disconnect within 30 ft of the mobile home wall, the communication circuit must have its own grounding electrode. In this case, or if the mobile home is connected with cord and plug, you must bond the communication circuit protector to the mobile home frame or grounding terminal with a copper conductor no smaller than No. 12.
Interior communications conductors. Keep communication conductors at least 2 in. away from power or Class 1 conductors, unless they are permanently separated from them or unless the power or Class 1 conductors are enclosed in one of the following:
2. Type AC, MC, UF, NM, or NM cable, or metal-sheathed cable.
You may place communication cables in the same raceway, box, or cable with any of the following:
1. Class 2 and 3 remote control, signaling, and power-limited circuits;
2. Power-limited fire protective signaling systems;
3. Conductive or nonconductive optical fiber cables; or
4. Community antenna television and radio distribution systems.
You may not install communication conductors in the same raceway or fitting with power or Class 1 circuits. Raceways may not support communication unless the raceway runs directly to the piece of equipment the communications circuit serves. Seal openings through fire-resistant floors, walls, etc. with an appropriate firestopping material. Make sure any communication cables you use in plenums or environmental air-handling spaces are listed for such use.
Sidewall pressure carries the risk of damaging the insulation of the individual conductors, putting the product's performance at risk. Follow these general rules to maximize safety.
• Do not exceed a pulling tension of 20% of the ultimate breaking strength of the cable (these figures are available from the cable manufacturer).
• Lubricate the raceway generously with a suitable pulling compound. (Check with the manufacturer for types of lubricants that are best suited for their products.)
• Use pulling eyes when working with manhole installations.
• For long underground runs, pull the cable both ways from a centrally located manhole to avoid splicing.
• Use pulling eyes on each end of the run. Do not bend, install, or rack any cable in an arc of less than 12 times the cable diameter.