Pathways in residential cabling
I have a once-in-a-lifetime opportunity to buy a newly constructed home, and design and install a structured cabling system. I would like to do this correctly and avoid the "gotchas," if possible.
Q: I have a once-in-a-lifetime opportunity to buy a newly constructed home, and design and install a structured cabling system. I would like to do this correctly and avoid the "gotchas," if possible. To expedite the installation, I have decided to install an all-in-one cable with two RG-6 coaxial cables, two speaker cables, and two Category 5e cables. I would hate to find that all-in-one cable is not the way to go, or that in five years or so down the road I should have installed Category 6 or fiber when I had the chance. Do you have any suggestions? Is fiber really too much for a residential network? If I did install fiber, should I install some kind of raceway to protect it, especially when going through the attic or to the distribution panel in the basement? How would fiber be terminated in the outlet? Is a wireless network worth considering, or is it just a novelty? As you can see, I have many questions. If you can make some suggestions, or can direct me to a source for answers, it would be much appreciated.
A: OK, so you are planning to build a family home that will be passed on to future generations, and are considering cabling it for year 2000 technology. In the future, there will always be a new, better way to do what you are doing today. While "everything old is new again" may aptly describe bellbottom pants and lava lamps, in telecommunications cabling, when it is old it is obsolete.
I recommend that you not install a bundled cable. First, you are not going to need two "speaker cables" at every voice/data outlet, or two RG-6 at each speaker location-I think you get the idea. And what are you going to do when some of the cables in the bundle become obsoleteellipseor the latest buzz phrase..."abandoned"?
I strongly believe that houses should be constructed with pathways within walls to allow for upgrading the low-voltage cabling. The cabling will have to be changed to accommodate new technologies, but the pathway will last for the life of the structure.
The tricky part will be making certain that you place outlets where you will need them in the future. Most home-appliance manufacturers are touting Internet-capable kitchen appliances. I have seen, and played with, several prototypes at trade shows. An outlet box with a flexible conduit back to your "network operations center" may some day contain the cabling that connects your refrigerator to "recipe central" for a report of what you can make for dinner based on the items in your freezer. But you would not have to gamble today on which cable to install. You could even wait until after you purchase the "smart fridge" and install the cable recommended by the manufacturer.
The ANSI/TIA/EIA-570A Residential Telecommunications Cabling Standard addresses two grades of residential cabling, but zero grades of residential pathways. But Carlon (www.carlon.com), a manufacturer of thermoplastic enclosures, fittings, and wire and cable management products, has done an excellent job in a publication entitled Carlon Structured Cable Management Systems.
Carlon presents the three M's-minimum, moderate, and maximum-sort of a good, better, and best of residential pathways:
- At a minimum, install an empty vertical chase consisting of one or more
2-inch flexible conduits from the distribution box area into the attic.
- For moderate coverage, to the vertical chase, add one flexible conduit run to every outlet where you think you may want to upgrade your cable in the future.
- For maximum coverage, to the vertical chase, add one flexible conduit run to every outlet.
The simple wireless control systems that I am using in my home today work very well. By that I mean that, so far, none of my neighbors are controlling my lighting or home-entertainment systems. And yes, once it matures a bit more, wireless (data) networking will be worth consideration. But for now, I like knowing with whom I am sharing my DSL service and intranet.
Fiber will not be "too much" for a residential network in the future, but which one you will need and which small-form-factor fiber connector will finally win the connector war remains undecided.
So, why not lighten up the contents (cables) and concentrate on the container? And for additional thought-provoking ideas, I suggest you read Residential Network Cabling, written by BICSI and published by McGraw-Hill.
Q: I recently completed a voice and data installation on a campus of eight buildings. I am finding noise on several pairs of some of the interbuilding backbone cables (100-pair armored twisted-pair terminated on 110 blocks). I suspect it is induced by one or more electromagnetic interference (EMI) sources. Will grounding the armor at the main crossconnect eliminate or reduce this problem? The problem is appearing on some, but not all, of the pairs, and is restricting the use of direct inward dial telephone lines. Any suggestions?
W. Andrew Deane, BSEE
Cable & Wireless Information Systems Ltd.
St. Michael, Barbados
A: Unless the eight buildings are very close together, I believe the interbuilding cabling to be "exposed." At a minimum, the cable shield should be bonded to ground at each end of the cable, and you should also install primary protectors.
Cabling is considered to be exposed to lightning unless it is installed in a large metropolitan area where buildings are close together and sufficiently high to intercept lightning. Or, unless the interbuilding cable is less than 140 feet (42 meters) in length and directly buried or in underground conduit where a continuous metallic conduit containing the cable is bonded to each building grounding electrode system. Or, is geographically located in an area of the country having an average of five or fewer thunderstorm days per year and earth resistivity of less than 100-W meters.
We do not often see this in the United States, because our National Electrical Safety Code requires that cable shields, support strands, and all other noncurrent-carrying metallic hardware be effectively grounded. Also, our National Electrical Code requires telephone utility companies to install primary protectors where telephone lines are exposed to lightning. Additionally, the NEC requires installers of private networks that include interbuilding cable to include primary protectors where cables are exposed to lightning. (A primary protector is required at each end of an interbuilding cable.)
I suggest that you add some outside plant "how to" material to your reference library. Two good places to start would be the BICSI 2001 CO-OSP Design Manual (see www.bicsi.org) and abc TeleTraining Inc.'s Volume 12-Practical Grounding: Theory and Design and Volume 13-Grounding and Bonding, 2nd Edition (see www.abcteletraining.com).
Donna Ballast is BICSI's standards representative and a BICSI-registered communications distribution designer (RCDD). Ques tions can be sent to her at Cabling Installation & Maintenance, in care of Chief Editor Patrick McLaughlin: firstname.lastname@example.org