Cabling Installation and Maintenance
Tech-savvy homeowners are demanding a new breed of cabling and equipment.
Steven Totolo / Total Voice Control
With the proliferation of new technologies available to homeowners, residential cabling will have to be upgraded to match these advances. Consumer products such as WebTV, Internet Phone, and games over the Internet will require wiring to handle the amount of information traveling through them. The standard home today uses wiring designed 50 years ago for applications that did not exist at that time. Homes must be wired for the requirements of today's homeowners as well as for products not yet designed.
A disruption in daisy-chained wiring can disable devices down the line (a). A star topology isolates the problem from other devices (b).
Half a century ago, home wiring was done in an ad hoc fashion. The first trades on the building site would drill holes to run their services. Subsequent tradesmen would later arrive and proceed to install their wiring in the existing wire paths. This practice resulted in electrical, telephone, and television cables strung through the same paths and holes throughout the home, which caused cable usefulness to degrade. Even with today's technology, such as 56-kbit/sec modems, household cabling can restrict modem data speed to half because the data must travel through telephone wire, which was not designed for this application. Consumers are generally unaware of this restriction and falsely blame hardware for the slower performance.
There are several methods of interconnecting wiring: daisy chain, bridge-tap, and star. Telephone lines are often daisy-chained from one room to the next. Should a break occur in the wire, several rooms could be affected. This arrangement is problematic because finding the location of the broken wire requires tracing the wire from tap 1 through tap 5. To repair the break, an installer would need to connect a new cable between taps 2 and 3, yet leave the remaining original wire intact. Equally problematic, taps 3 to 5 would be kept out of service during repair, interrupting regular phone use.
Another method of connection is a bridge-tap or splice, which also weakens phone line signals because noise can be induced at this point. A similar problem affects TV cable because splitters placed along the line weaken the signal every time they are used. When additional connections are left unterminated or unconnected to a device, reflections and interference can affect video distribution.
Yet another problem with existing wiring is the installation process. Wires that run along joists and studs are usually held in place with staples. The standard staple gun fires the staples hard into the cable, deforming and changing its characteristics and performance. Sometimes cables are placed into awkward locations or run through tight turns, pinching the cable. These practices, while not detrimental to wiring of the past, are harmful to higher-speed cabling.
Moreover, as homeowners' needs changed, additional cabling might have been installed that did not match the type and quality of the original wiring. Also, most homes were only wired for one cable-TV connection and one or two phone connections. Unfortunately, this approach does not accommodate today's lifestyles.
The star topology is considered by the industry to be the proper way to install new cabling. In this formation, all cables start at one location, usually at the entrance of the telephone and cable-TV wiring site to the home, and travel directly to their intended destination. This scheme provides maximum flexibility for installing and testing home local area networks or intercoms and improves the signal quality and installation of new services.
Properties of new cabling
Alternating current flowing through household wiring generates a magnetic field. When this field comes near another conductor, current flow is induced in the wire. With twisted-pair cables, the magnetic field causes the current to flow in one direction before the twist and in the opposite direction after the twist. Therefore, the current induced into the cable is canceled out.
Standard telephone wire is constructed with either two, three, or four insulated conductors gathered together and jacketed. The wires are placed randomly in the jacket, causing conductors to run parallel to each other or sometimes to become twisted. This is known as Category 1 wire or plain old telephone service (POTS) wire.
Typical Category 3 wire has eight conductors in four pairs, with each pair twisted together at two to six twists per inch of wire. It has a usable data bandwidth of 10 MHz and is most commonly used for low-speed data applications such as computer modems and telephony. Despite the low cost for Category 3, its demand is dwindling because price differentials between it and the superior Category 5 are diminishing.
Category 5 wire has four pairs, each of which is twisted together at least three twists per inch, resulting in a bandwidth of 100 MHz. The number of twists per inch is proportional to the amount of noise rejection. In simple terms, the more twists a wire has per inch, the better it rejects noise and the greater its bandwidth.
Manufacturers are bundling fiber-optic, twisted-pair, and coaxial cable to meet home networking needs.
There are Category 2 and Category 4 cables, but they are not widely used. Category 5E (Enhanced Category 5 with 100-MHz bandwidth), Category 6 (250-MHz bandwidth), and Category 7 (600-MHz bandwidth proposed) are currently beyond home requirements and their higher cost is unwarranted for residential cabling.
RG-6 is an improved version of the standard TV cable RG-59. It has a slightly larger diameter, but the reduction in the signal level at high frequencies is less than the RG-59. That means cable channels at the higher frequencies (i.e., channels 70-125) will not attenuate as much. Consequently, satellite-TV dish signals will travel further when RG-6 is used.
Fiber-optic cable has glass or plastic strands that are used to carry the signal. Fiber optics uses light pulses instead of electrical signals for transmitting information, eliminating the concern about electromagnetic interference. More information can be transmitted using fiber-optic cable since the light pulse levels degrade less over distances as compared to copper cables, resulting in a bandwidth greater than 500 MHz per mile.
Fiber-optic cables consist of a glass or plastic core and cladding surrounded by a protective coating. The core and cladding are part of the same glass or plastic rod but have different optical properties. Light pulses are injected into the core. As light pulses travel down the cable, the cladding, acting as a mirror, reflects the pulse back to the center of the core. A plastic protective coating, called a buffer, surrounds the core and cladding.
There are two basic types of fiber-optic cables: multimode, with a core width of 62.5 or 50 microns, and singlemode, with a core width of 8.3 microns. (By comparison, the average human hair is 80 microns thick.) Multimode fibers provide a number of paths for light pulses to follow as they traverse a cable. The wavelength of the light source and size of the core determine the number of modes. Singlemode has only one path.
Structured wiring for home automation and home networking is a new technology. The term "structured" is derived from the construction of a cable assembly of several cable types. The bundle is wrapped with a spiral nylon rope or encased in a material such as polypropylene. The assembly comprises two RG-6 and two Category 5 cables. Some companies also incorporate two 62.5-micron fiber cables. A different color sheaving identifies each cable. One company colors the RG-6 black and pink, the Category 5 lines blue and yellow, and the fiber cables orange and gray. This package enables the installation of up to six cables with a single cable run, reducing installation time. Since the bundle is approximately 5/8 of an inch in diameter, it can be difficult to install the cable in tight spots. This problem is especially true for structured wires that have overall sheaving because it increases the diameter and stiffness of the bundle.
Installation of wiring
With proper installation techniques, crosstalk and noise can be reduced and signal quality improved. Crosstalk occurs when conductors are located parallel to each other and the signal on one conductor is coupled to the other. Typically, two users will notice crosstalk when an outside phone conversation can be heard by one party but not the other. Noise from fluorescent lights, motors, or electrical appliances can also be coupled onto the wiring. To reduce these problems, Category 5 and RG-6 cables should be kept at least 12 inches away from electrical wiring when they are parallel to each other. When cables cross, they should be kept at 90° angles from each other. Furthermore, electrical and Category 5 or RG-6 mounting boxes must be kept at least 12 inches from each other, using at least one stud distance between each service.
When installing twisted-pair cable in the home, maintain proper spacing between different types of cable.
Cabling should be attached using hook clips or other wiring retainers that do not crush conductors. If there are many cables in a path, hangers should be affixed to support the bundle. Cable ties can be applied but should not be over-tightened. Excess tightening can pinch the wiring, whereas a loose tie will allow cables to slide easily back and forth within the bundle. Using hook-and-loop straps during the installation can ease cable pulling since the straps can be nailed to studs or joists. Cables can then be pulled through the loose opening with little force. To reduce the risk of damaging or tangling the cables, pulls should be made in stages when the paths are long or have many turns. Never exceed a stretching or pulling tension of 25 lbs since this may cause the wire pairs to untwist.
Whenever cable bends are required, maintain a minimum turning radius of four times the cable's outside diameter (for Category 5, approximately 1 inch; for RG-6 and fiber, approximately 1.2 inches).
Twisted-pair cable must remain twisted as close as possible to the point of termination. Untwisting should not exceed a half-inch for Category 5 or 1 inch for Category 3. The jacket of the cable should only be stripped back as much as required to perform the termination of individual pairs.
Fiber-optic cables must be installed in housings with at least an extra 3.3 ft of length for termination. The connection box must have the capacity to secure the cable in some form, while ensuring a minimum bend radius of 1.2 inches. Multimode connectors should be beige, while singlemode should be identified with blue connectors.
Cable runs must originate from point-of-use and terminate in a central location, usually a utility closet or near the location where services enter the home. This cabling is referred to as "homerun" cabling. In other words, cables enter a service junction, or gateway, that interconnects phone, video, and network utilities to access points located throughout the home. Short interconnecting cable can then be used to link these services.
Home services locations
Wiring terminations are normally run to two locations in the kitchen, one in each bedroom, one in the bathroom, and three in the living room, family room, or den/computer room. Each termination point has two Category 5 and two RG-6 cables with optional fiber connections in the living room, family room, and den/computer room.
A network hub, located in a service closet, furnishes connections from the home's Internet provider via either a cable modem or asymmetric digital subscriber line or a connection to a phone line modem connected to a PC. The hub allows connections to be added as new computers are brought into the home, creating a home local area network. Such a network makes moving a computer to another room simple, because it requires wiring changes in the service closet only.
A residential service closet should accommodate several types of services.
Another equally important device located in the service closet is a cable-TV distribution amplifier that provides an individual signal to each access point in the home, where necessary. It may also include a video modulator that can be used to place a front door or baby's room camera to a selected channel available throughout the home. This device enables homeowners to view a person at the front door when the doorbell rings or peer into a baby's room when she cries. Video equipment in one room can also be viewed throughout the home by sending its output through the second RG-6 to a video modulator. Selection and control are enabled through infrared (IR) receivers and transmitters via twisted-pair cabling to devices through an IR repeater installed in the wiring closet.
With some of the largest telephone and Internet equipment manufacturers paving the way for voice over Internet protocol, the need for high-speed communications devices or wiring will be critical. Plain old wiring will just not be up to the task for real-time, interactive videoconferencing or multiplayer gaming.
Steven Totolo is president of Total Voice Control (Ottawa, ON, Canada), a home automation specialist and a member of the CABA Standards Committee. He can be reached at tel: (613) 795-7117; fax: (613) 737-5323; e-mail: [email protected]. This article was submitted by the Continental Automated Buildings Association, www.caba.org.
FCC mandates Category 3 for all new projects
Patrick McLaughlin
On Jan. 10, the Federal Communications Commission (FCC) released an order stating that builders and contractors installing twisted-pair telecommunications wiring in new-construction and retrofit projects must install at least Category 3-rated cable (see related story on page 119). The order applies to wiring installed inside homes and other buildings. It does not mandate the use of twisted-pair wiring over other media types (such as fiber-optic, coaxial, and wireless) but does demand that when twisted-pair is used, it must be at least Category 3-compliant.
The FCC originally considered implementing this order as a two-year interim standard but ultimately opted to make it a permanent order. BICSI (Tampa, FL) and the Telecommunications Industry Association (TIA-Arlington, VA) were among the groups that issued comments to the FCC, and BICSI member Ronald Provost chaired an ad hoc FCC advisory group that examined the issue. BICSI filed its proposal with the FCC in August 1997.
null
Pros and cons of upgrading residential cabling
Some organizations promote new home cabling while others oppose it. Wiring Americas' Homes is an industry campaign that encourages consumers and builders to prepare their homes properly to embrace current and future technologies by installing or upgrading residential wiring. It views the benefits of a "connected home" that "...empowers the homeowner to maximize the potential of technology to satisfy personal lifestyle needs."
Alternately, companies that oppose new wiring installations often do so because they believe that renovations to existing homes generate an unnecessary mess. They propose that by using wireless technologies such as HomePNA or radio- frequency (RF) devices or power-line carrier (PLC) devices, users can achieve the same goals as adding new wires but without the need to rip up walls. There are advantages to both proposals, and a combination of the two may be appli cable in some instances. New wires are easier to install and troubleshoot in new homes, before the walls are covered, while HomePNA, RF, and PLC devices are easily installed into existing homes by attaching them to walls or plugging them into wall outlets.