If you think of the home as a body and things like telephone systems, computer networks, security systems, doorbells, entertainment systems, and other services within the home as the organs that carry out day-to-day functions, low-voltage cabling is the circulatory network of capillaries, veins, and arteries that transport the voice, data, audio, and video signals necessary to keep that home network functioning. As the sixth installment in a 12-part series that will prepare electrical contractors to take the test to be certified as home technology integrators (HTI), this article will discuss the various styles of cabling available and the different uses for which they're designed.
A wire primer.
Low-voltage wiring varies by type and gauge using the American Wire Gauge (AWG) system. In simplest terms, the higher the AWG number the thinner the wire. For example, a 10 AWG wire has a diameter of 2.59 mm, whereas a 24 AWG wire has a diameter of .51 mm.
There are basically two types of low-voltage wire: twisted-pair and coaxial.
Unshielded twisted-pair (UTP) cable is by far the most widely used today. As such, the Electronics Industries Alliance (EIA) and the Telecommunications Industry Association (TIA) have classified and developed standards for several types of UTP cable.
Cat. 1 — Once used for telephones, Cat. 1 is still used for ISDN and doorbell wiring. This two-pair cable has a maximum data rate of 1 Mbps.
Cat. 3 — Used for telephone wiring, Cat. 3 has a maximum data rate of 16 Mbps. This designation applies to 100-ohm UTP cables that have four pairs of copper wire.
Cat. 5/5e — This is the most commonly installed medium. As with Cat. 3 cable, this designation applies to 100-ohm UTP cables with four pairs of copper wire. The difference is that it has a maximum data rate of 100 Mbps.
Cat. 6 — This newest classification also applies to 100-ohm, four-pair cables.
Shielding is often required to make communications possible. Shielded twisted-pair (STP) copper wire includes a screening layer to protect the wires from outside interference. The individual pairs are each wrapped in a protective shield. Those four pairs are then wrapped again in another shield. Two varieties of STP cable are available for communications installations. Ethernet networks that use 100-ohm STP and 150-ohm STP are used for Token Ring network architecture. Screened twisted-pair (ScTP) wire has only a single shield and is less expensive than STP. Unlike STP, the individual pairs in this cable aren't wrapped in a shield.
When working with twisted-pair cables, it's important to be able to identify individual wires within the cable. The wires can be easily identified by their colored insulation. All manufacturers follow the same color-coding scheme. This allows the installer to more easily ensure that the correct wires are terminated properly at each end of the cable run.
For each pair of wires, one wire is considered the “tip” and the other is called the “ring.” The primary color in a four-pair cable, such as Cat. 5e, is the tip, which is usually white with a tracer or stripe that's the same color as the pair's solid color wire, which is the ring.
Coaxial cable is typically used for cable TV or video applications, such as surveillance and security. Coax cable was historically designated as RG, or radio frequency, cable. It's now referred to as Series-X cable. The “X” relates to the construction of the cable based on several factors, including the center conductor diameter, outer cable braid percentage of coverage, dielectric composition, impedance, and whether the center conductor is solid or stranded. Common examples are Series 6 coax cable (RG-6) and Series 11 coax cable (RG-11).
Coax cable generally provides a much higher bandwidth and more efficient protection against EMI than twisted-pair cable. A dual-shielded coax cable, for example, uses aluminum foil for the high-frequency shield and aluminum braid for the low-frequency shielding. Coax cables can also have additional shielding. A trishield cable has two foils and a braid, whereas a quad-shield cable employs two foils and two braids. A quad-shield coaxial cable construction is recommended because it provides the best shielding characteristics.
Residential structured cabling systems (RSCS), discussed later in this article, should employ Series 6 coaxial cabling for transmission of digital video signals from the distribution device to the outlets. Series 6 coaxial cable has the following features:
More bandwidth than twisted-pair cable, which is necessary for digital video signal transmission.
Coated/aluminum foil shield over the dielectric, which is necessary to shield against high frequencies.
Braided shield over the coated/aluminum foil, which is necessary to shield against low frequencies.
Characteristic impedance of 75 ohms.
Coaxial cabling requires that all the outlets and equipment serviced by coaxial cabling use coaxial patch cords as well as equipment cords. The cords provided with consumer audio/video equipment or devices are only good for use as equipment cords. Additionally, there's a distinction between patch cords and equipment cords.
Cable certifications and standards.
Underwriters Laboratories (UL) certifies all twisted-pair cables for data networking, including UTP and STP. Network cable falls into one of the following UL safety standards:
UL 444 “Standard for Safety for Communications Cable.”
UL 13 “Standard for Safety for Power-Limited Circuit Cable.”
The UL LAN Certification Program addresses not only safety, but also performance.
The ANSI/EIA/TIA-570-A standard defines two grades of residential premises telecommunications cabling for a home based on the nature of service required: Grade 1 and Grade 2.
Grade 1 cabling uses the following components to provide a generic cabling system that meets the minimum requirements for telecommunications services:
One 100-ohm, four-pair UTP cable and connector that meets or exceeds the requirements for Cat. 3. The use of Cat. 5 cable is recommended.
One 75-ohm, Series 6 coaxial cable. The use of quad-shield cable is recommended.
Grade 2 uses the following components to provide a generic cabling system that meets the requirements for basic, advanced, and multimedia telecommunications services.
Two 100-ohm, four-pair UTP cables and connectors that meet or exceed the requirements for Cat. 5. Cat. 5e cable is recommended.
Two 75-ohm Series 6 coaxial cables. Again, the use of quad-shield cable is recommended.
Two multimode fiber optic cables are optional.
ANSI/TIA/EIA-232 supports a point-to-point connection over a single copper cable, so only two devices can be connected. This cable is also used to connect modems to telephones.
ANSI/TIA/EIA-422 supports multi-point connections, whereas ANSI/TIA/EIA-423 supports only point-to-point connections. Both standards are backward compatible.
ANSI/TIA/EIA-485 supports multi-point communications and several types of connectors. It can support 32 nodes per line because it uses lower-impedance drivers and receivers.
FireWire is Apple's version of high-performance serial bus that complies with IEEE 1394 Standard for High-Speed Serial Buses Allowing Gigabit Ethernet. It provides a single plug-and-socket connection for computers on which as many as 63 devices can be attached with data transfer speeds up to 400 Mbps.
Like universal serial bus (USB), 1394 supports both plug-and-play and hot-plugging, and also provides power to peripheral devices. The main difference between IEEE 1394 and USB is that IEEE 1394 supports faster data-transfer rates and is more expensive. For this reason, it is primarily used for devices that require large throughputs, such as video cameras.
In addition to twisted-pair and coaxial cable, there are a variety of specialty cables required to connect various subsystems used throughout the home. They include speaker cables, thermostat cables, security cables, and bundled or composite cables.
Speaker wire is typically sized at 14 AWG or 16 AWG, and is used for entertainment systems like stereos and speakers. AWG 14 and 16 cables represent the best compromise between line loss, cost, and ease of installation.
Thermostat cables are 18 AWG and designed with two, five, or seven wires.
A typical 18 AWG thermostat wire is rated at 300V and available in three styles:
2-conductor for “millivolt” heat-only systems or damper motor control.
5-conductor for standard HVAC systems.
7-conductor for typical heat-pump systems.
Other applications for thermostat wiring include touch plate systems, burglar alarms, intercom systems, doorbell and signal systems, and remote control units.
A security system also uses specifically designed cables. A variety of gauges are used, each with a specific use.
22 AWG, 2-conductor copper wire connects inside sounding devices to control panel terminals.
22 AWG, 4-conductor copper wire connects consoles to control panel terminals.
18 AWG, 2-conductor copper wire connects external power supplies to control panel terminals.
14 AWG, single-conductor copper wire is used to ground the security system.
Cat. 5 or coax cable is used to connect the security camera.
You'll also run across specialty cables designed to connect multiple subsystems in the overall home network. A bundled or composite cable is an assembly of two or more — usually four — cables continuously bound together to form a single unit. Typical bundles include:
Two coaxial and one Cat. 3 or 5 cables.
One Cat. 5/5e and two speaker (14 AWG or 16 AWG) cables.
Two Cat. 5/5e and two RG-6 (coaxial) cables.
Two Cat. 5/5e, two RG-6, and two fiber-optic cables.
Two Cat. 5/5e, two RG-6, and two pairs of 14 AWG speaker cables.
Making the connection.
Now that you have a clear understanding of all the types of cables used in a residential structured cabling system (RSCS), it's time to turn to the devices used to connect all of these cables into a functional system. A structured cabling system includes not only the wiring media mentioned above, but also distribution panels, patch panels, connectors, jacks and plugs, and termination blocks.
A structured cabling panel is contained within the distribution device (DD), or distribution panel. The panel serves as a termination and connection point for wires running between the voice and data subsystems, acts as the center for a star wired network, connects access providers to the residence, and allows for easy moving modifications and changes.
A typical structured cabling panel contains a telephone line distribution module, two Cat. 5e voice and data modules, and a six-way video splitter.
A patch panel is used to interconnect data networking and voice systems. The patch panel interconnects backbone cable systems to network distribution cable systems. Most common patch panels are designed to accept RJ-45 jacks, which are terminated on the ends of UTP cables.
An insulation displacement connector (IDC) is typically used to terminate twisted-pair cables. IDCs allow you to terminate an insulated conductor without stripping away its insulation. Two common examples of IDCs include the 66-block and the 110-block. The former aren't rated for high-performance data installations and are commonly used in voice (telephone) applications only. They have four columns of 50 pins, so they can accommodate either 25-pair termination or 50-pair terminations. Suitable for either voice or data applications, 110-block IDCs provide a low-resistance, gas-tight connection with 100-pair and 300-pair configurations.
Jacks — the female end — and plugs — the male end of a jack-and-plug system — come in several forms. Jacks with eight conductor positions can be broken down into two categories. An 8P8C jack is modular and has eight positions that are occupied by eight wires. They're used to interface twisted-pair cables with equipment lines or patch cords. RJ-45 jacks are 8-conductor jacks designed to accept RJ-45 plugs. Jacks are normally wired to the requirements set forth in the T568A or T568B standard.
Jacks with six conductor positions can also be broken down into two categories. The 6P6C and RJ-11 jacks have only six conductor positions occupied by a total of six wires. The RJ-11 connector, which can be either a jack or plug, is used for terminating Cat. 3 cable.
PBX telephone systems commonly found in multi-dwelling units make use of 25-pair copper wires to interface the entrance facility and cross-connect fields.
The QuickPort S-Video Module allows you to run any S-Video signal through any high-quality Cat. 5, 5e, or 6 cable.
RCA connectors are used for line-level audio and/or composite (component) video routing.
BNC and the Type F connectors are used for coax cable. The F-series connector is used for modulated radio frequency applications like cable TV, while the BNC connector is usually used for networking and video applications.
According to the TIA/EIA standard for residential wiring, a minimum of one outlet location shall be installed within each bedroom, and the kitchen, family room, and den. The standard adds that outlet locations should be provided to prevent the need for extension cords. Additional outlet locations should be provided so that no point along the floor line in any wall space is more than 7.6 m from an outlet location.
Informing the homeowner.
After installing, testing, certifying, and troubleshooting any problems with the wiring system, it's helpful for the homeowner to understand the residential wiring infrastructure and its components. Such training can center on giving the homeowner basic knowledge and understanding of aspects of the installation, such as the location of the termination points, the basic system configuration and general routing of the cables, and which circuits serve which rooms.
Always give your clients the chance to ask as many questions as possible, and give them clarification in your answers. The cabling that supports those life systems throughout the home is every bit as important as the devices themselves, so knowing how to take care of it is valuable to the homeowner.
Dusthimer is publisher of Cisco Learning Institute Press, York, Pa.
Sidebar: Avoiding Interference
A wire positioned too close to sources of electrical noise or radio noise may act as an antenna impeding the signal. If stray electrical signals enter the cable, they interfere with the desired signal by distorting the amplitude and/or frequency of the data, confusing the receiving device and forcing the network to retransmit the data. For instance, AC power line noise coming from a nearby video monitor or hard disk drive can be enough to create errors in a computer system by changing the shape and voltage level of the desired signal.
The biggest source of signal distortion for copper wire occurs when signals inadvertently pass out of one wire within the cable and onto an adjacent one — a phenomenon called crosstalk. Resistance can also decrease the strength (energy loss) of a signal by way of a process called attenuation. Noise is unwanted energy that can degrade and distort the quality of signals. In the case of analog signals, the signal becomes noisy and scratchy. In digital systems, bits can become indistinguishable, which translates into network instability.
In addition, there are external sources of electrical impulses, generated from items like fluorescent lighting, electrical motors, and cordless phones, which can interfere with the quality of electrical signals on wires. These types of interference are referred to as electromagnetic interference (EMI) and radio frequency interference (RFI). In general, any device or system that generates an electromagnetic field has the potential to cause EMI. However, properly grounded systems can minimize or eliminate problems with EMI.
Sidebar: Who Wants to Be an HTI?
Electrical contractors can now become certified as home technology integrators (HTI). CompTIA, in conjunction with the Internet Home Alliance and a cornerstone committee of Fortune 1,000 companies, has developed a two-exam certification process. The material in this 12-part series is part of a 50-hr training program designed to prepare individuals to take the HTI+ certification exam. Throughout the year, the articles in this series will include excerpts from the HTI+ training program developed by the Cisco Learning Institute along with industry partners Leviton Manufacturing, HAI, Premise, Interlogic, and Bluevolt. This program will prepare electrical contractors and their employees to capitalize on this new and financially rewarding segment of the field.