Wiring outlets should not be placed in the same stud cavity as HVAC cold-air return ducts. Similarly, they should be at least one stud-cavity away from 120V/240V AC wiring. Ideally, all structured wiring should stay 12" from 120V wiring, and cross at right angles where necessary.

Home Cabling Part III

Brian Karas

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Brian Karas

Wiring outlets should not be placed in the same stud cavity as HVAC cold-air return ducts. Similarly, they should be at least one stud-cavity away from 120V/240V AC wiring. Ideally, all structured wiring should stay 12" from 120V wiring, and cross at right angles where necessary.

Brian Karas is a Senior Network Support Engineer for the leading Frame Relay equipment provider by day, and a Home Automation and DataComm consultant and installer 'the rest of the time'.


Now that we've discussed the basic merits of a good wiring system, and gone over some basic wiring closet arrangements, we need to take a look at the typical rooms in a house, and where we need our cables to go. Fortunately, this is a pretty simple task.

If you've ever read through the NEC (National Electrical Code) for the U.S., you'll see, among many other things, the requirement for 'convenience outlets' to placed strategically in any dwelling in order to facilitate easy and safe access to the 120V power they provide. This concept can (and should) be carried over to the placement of your structured wiring outlets. Many people plan for only one structured wiring outlet per bedroom, maybe 2 in a large living/family room, and none in other rooms. However, I believe these structured wiring outlets should be located to provide maximum flexibility with room arrangements, and this typically requires two outlets per bedroom, and least 2, if not more, in larger rooms like living rooms, family rooms, etc. Also, don't overlook rooms like the Kitchen, Laundry, and Bathrooms, and outdoor areas or garages. If you plan to have a finished basement, then you'll want to provide media outlets there as well. Because every houses floorplan is unique, it's difficult to give more precise information regarding location of these media outlets. Just imagine your house in it's finished state, and try to ensure that every location that is likely to have a phone, computer, camera, TV, or IR device has a structured wiring outlet in it's vicinity. For room with long walls, or doorways separating their walls, plan for two or more outlets along these walls.

The next step is to determine how much cable will be needed, keep in mind this doesn't have to be a very accurate estimate, as most cable comes in 500'-1000' spools. Just multiply the total number of planned outlets by an average run length, add 5% for waste, and round up to the nearest 500 or 1000 foot mark. You'll typically find that buying in 1000' spools is the cheapest way to go, and with a 1000' spool of Cat5 running around $80 (including delivery) it's not very costly to err on the side of caution.

boxpic1.jpg (84883 bytes)Before the cable can be pulled, we'll need to drill some hole to pass the cables through, and place our modified J-boxes or low-voltage brackets in the appropriate locations. I say modified J-boxes because you'll want to cut the backs off of regular plastic boxes before nailing them to the studs. This will keep your cables from getting kinked or severely bent when the faceplates are installed. Cat5 and RG-6 have minimum bend radius' that must be met in order to achieve peak performance. Sharp bends will degrade performance. If you don't want to cut the backs off of the J-Boxes, you may be able to find low-voltage brackets at your local home-improvement store, or on-line via mail-order sites like mine. I still prefer the J-Boxes, they're cheaper, easier to find locally if you run out, and the sides offer a little more protection and support to the faceplate and cables.

Whichever you choose, J-box or LV Bracket you'll want to make sure that they are the same height from the floor as the 120V work boxes that the electrician has placed. The best way to do this is to cut a scrap of wood to serve as a spacer for placing the boxes.

Nail the boxes, or brackets, securely to the studs.

cablehole.jpg (68249 bytes)You'll find the actual pulling of the cables will go faster if you can plan their routes ahead of time, and pre-drill as many holes as possible. A long spade bit works well for this, or a regular bit with an extension. This makes it easier to drill holes overhead, or to drill floor holes without kneeling down. CAUTION: Always look at the 'other side' of the hole to make sure that you won't damage any existing pipes, wires, ducts, etc! A 5/8" hole is usually sufficient to allow 2 Cat5 cables and 2 RG-6 cables to be easily pulled through. Space the holes about 2-3" from the stud, to avoid hitting any nails or screws that have been used to build the framework.

Wiring outlets should not be placed in the same stud cavity as HVAC cold-air return ducts. Similarly, they should be at least one stud-cavity away from 120V/240V AC wiring. Ideally, all structured wiring should stay 12" from 120V wiring, and cross at right angles where necessary. onlychoice.jpg (59666 bytes)However, it is often difficult to adhere 100% to this rule, try to maintain as much separation as reasonably possible to minimize interference from the high voltage wiring. Sometimes, as you can see from the following picture, you're left with no other choice. This outlet box was used as a volume control, no interference is present in the finished job, but you don't want to make this a habit.

Once you have your holes drilled, and the boxes mounted, you can begin to pull and secure the cables. It is often beneficial to have a helper on hand, however it is possible to do the job alone. Start by locating the cable boxes and spools at the wiring center location. To speed the process you'll want to pull several cables at once, typically you'll be pulling the standard 2 Cat5, 2 RG-6 bundle. I've found that it works best to buy the Cat5 in boxes, and the RG-6 in spools. The spools will require some sort of cable carrier to support them, this cable carrier can be easily made from scrap wood.

cablecarrier.jpg (79412 bytes)When pulling the cables take extra caution not to kink or snag the cables, and don't pull them too fast, or else you may damage the jackets from friction and heat buildup.

Once the cables have been run to the outlet box, you'll want to secure them at the box, and along their path, and then cut them off and label the bundle. A standard electricians staple can be used to secure the cables to the 2x4's. Be careful not to damage the cables from hammer blows, or by driving the staple too deep. You should be able to just barely pull the cables out of the staple, they should not be bound or 'stuck' behind the staple.

You may want to wait to secure the cables in the basement, or along the main paths so that you can bundle the cable together into one large bunch, rather than several smaller bunches. Depending on your layout, you may be best off using cable hangers, available at most DIY centers, or on-line suppliers. These hangers can accommodate up to 100 cables easily, and are typically hung from I-beams or joists.firestop.jpg (73225 bytes)

Before you cut the cables from the spool, make sure you leave plenty of slack to allow the cables to be neatly routed in the wiring closet.

The last step in the cable pulling process is to firestop any holes you drilled that pass between floors. A bit of insulation can be used for this, or Firestop Caulk ($13.00/tube) made specifically for this task can be used instead.
Next month we'll cover the termination of the cables, and the installation of wiring closet components.


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