Brush up on some cable pulling techniques before beginning the rough-in stage of a home network project
Once you've designed a home network, chosen the hardware, and specified the wiring, you might think you're in the clear — just a little manual labor and cable pulling and you're done, right? As it turns out, navigating the maze of studs, pipes, and vents that crowd the already-tight area hidden behind drywall can require just as much planning as the design of the system itself. If you're not competing with one trade for space, you're making considerations for the placement of the network elements.
This article, the ninth installment in a 12-part series that will prepare electrical contractors to take the test to be certified as home technology integrators (HTI), focuses on the rough-in stage of home networking projects for both new construction and retrofit work. As with any other wiring project, a home network can be challenging to install in an existing building, but new construction presents its own set of issues that can slow down the process and create problems for the installer as well.
New construction allows easier access for running the required communications cables, but requires careful coordination with the construction manager. Construction schedules can be fluid, and it isn't uncommon for changes to take place throughout the life of the project. Scheduling mistakes are easily corrected, but they invariably cost someone money. However, errors can be minimized if you communicate well with others. Meeting with the construction manager on a regular basis helps define responsibilities and expectations.
The blueprints for a project should show all of the details you'll need to create a plan of attack. Consider the following questions when reviewing the plans. Has the roof construction been completed with rafters or trusses? What is the thickness of the walls? Are the interior walls constructed with 2×4 in. wood or metal studs? What is the thickness of the exterior walls? What is the stud spacing for the interior and exterior walls?
And remember, all trades typically have a rough-in and finish phase and must be appropriately scheduled. Plumbers and HVAC crews also have work to do once the walls are constructed. Ideally, the HTI is the last trade to perform any work before the drywall crew shows up. So figure this into your game plan and be prepared to work around these obstacles.
When installing data and voice cables, remember that low-voltage cabling has its own set of standards, which outline specific pulling tensions, bending radii, and spacing requirements from electrical conductors. Installing VDV outlets too close to electrical outlets can cause interference in the lines. In general, you should avoid mounting VDV and electrical outlets on the same stud. You should also avoid routing the cables in the same wall cavity as the electrical conductors and outlets.
Before you start to pull any cables, clearly identify all of your outlet locations. Home network outlets should match the height of the electrical outlets. Under-counter outlets for telephone, data, or video should match the height of the electrical wall switches. Handicap outlets for telephones are generally located 48 in. above the floor. Standard wall phone jacks should be mounted 60 in. off the floor.
When codes allow it, mud rings or drywall rings are preferable to outlet boxes because they allow for a larger bend radius than cables coiled inside of an outlet box. Use a permanent marker to label each cable as you mount each ring.
Once you've installed the mud rings and identified the location for the distribution device, it's time to address cable routing. In a commercial environment, it's standard practice to route cables along or perpendicular to building lines. In a residential installation, it's acceptable to take the most direct route between a distribution device and an outlet. The most important thing to remember is that you must separate communications cables from the power cables by at least 6 in., and all intersections should be at 90° angles. Routing cables parallel to joists will minimize the number of holes you have to drill in the studs. Try to drill holes along a route that will accommodate more than one cable run.
The following NEC references define rules for protecting electrical conductors in wall cavities and can also help protect structured cabling systems:
Cable runs through framing members must be located 1.25 in. or further from the nearest edge of that framing member [300.4(A)(1) and (2)]. If you can't meet the 1.25-in. rule, you must protect the cable with a steel plate or bushing that's at least .0625 in. thick.
Cable runs in intermediate and rigid metal conduit, rigid nonmetallic conduit, and electrical metallic tubing are exempt from the 1.25-in. rule.
Cable that runs through metal framing members without conduit must be protected by a bushing or grommet.
When working in a two-story home, it's usually best to drill down through the floor joists to create a pathway for outlets located on the second floor. You'll most likely want to route cables along the ceiling of the first floor, and then branch off to feed outlets on both levels. After drilling the hole in the floor joist, it's helpful to take a scrap piece of wire that's a foot or two long, tie a knot in one end, and drop the other end down through the hole. It will serve as a marker to identify the outlet location, and it will also provide a convenient pull string to attach the cable when pulling it up to the outlet above.
It's best to stage, or set up, cable reels at a single location. And it's often easier to install the distribution device after the cables are pulled into place. Security cables are typically installed in a separate distribution device in a different room. You should stage the security cables at the location of the security distribution device.
Most cables in a residential environment are pulled over or along the ceiling joists. In a two-story home, the first floor ceiling joists are the floor joists of the second floor. It's easier to pull the cables up over the first joist rather than through the top plate of the wall cavity that will contain the distribution device. If an outlet calls for two coax cables and two Cat. 5 cables, all four cables should be pulled in at one time.
When pulling toward an outlet on the second floor, stop the pull at the pull wire that you left for the outlet above. Then pull enough slack to reach the mud ring and provide a small service loop. Next, tie the ends of the cables to the pull wire, but don't pull them up to the outlet at this time. Go back to the staging area and begin the next pull. It's more efficient to pull all cables without interruption.
Label each cable run as you pull it. Place a label on the end of the cable and place a temporary label with the same identifier on the box or reel.
It's generally acceptable to allow cables in a residential environment to lie above the joists. If it's necessary to fasten the cables, Velcro cable ties are preferable to nylon cable ties. If you find it absolutely necessary to use staples to secure a cable in place, use those with insulators to prevent placing undue pressure on the cable jacket.
You should mount the structured media center (SMC) at a height such that the main work area is at eye level. The SMC is available in a variety of lengths and will fit between standard 2×4 in. studs. You should mount multiple SMCs next to one another at the same height. A completed installation should be flush with the finished wall.
Remove the proper size and number of knockouts in the cabinet, and install grommets in the holes to protect the cables from chaffing. Re-label the cables per TIA/EIA standards at a point about 4 in. to 6 in. beyond where they enter the cabinet. The standard specifies that all hardware termination units must have some sort of unique identifier, marked on the unit or on its label. Coil the cables for storage in the cabinet until the finish phase of the project. You can keep the wires organized with strings, zip ties, tie-wraps, or Velcro. Be careful not to use any ties that have metal in them because they may interfere with the signals carried on the wire.
You shouldn't secure the door of the SMC until after other trades are finished working in the area. However, you can protect the interior of the cabinet and the cables from dirt or harm by covering the opening with a piece of cardboard.
Keep in mind that installing structured cabling in an existing home can be very intrusive. Challenges for a retrofit installation include running cable through an existing wall and establishing a suitable location for the SMC. Depending on the difficulty and complexity of the installation, you could end up producing a significant amount of dirt and noise during construction. In fact, you may find that working certain days of the week or certain times of day based on the homeowner's schedule may be better for some of the harsher aspects of the work.
You should first try to secure any blueprints or drawings of the home, keeping in mind there may have been changes since the house was built. An as-built drawing is a more accurate reflection of the actual building. Verify everything before beginning construction. Make sure to include a contingency clause in the installation contract to cover you for unexpected findings during the installation process.
When pre-surveying the installation, identify walls that can be fished or through which you can run cables. Look for vertical alignment when running cables through more than one floor. Outside walls are generally more difficult to fish because they're filled with insulation. Some walls will be equipped with horizontal cross members that are designed to act as a firebreak; these walls are nearly impossible to fish. For that matter, any wire pulling between floors in a multi-level house after construction can be tricky business.
Older telecommunications cable within a building can sometimes be re-used. Technologies like Home Phoneline Network Alliance (HomePNA) will allow network signals to pass over existing telephone lines. Speed, however, will be a limiting factor for high performance. Most technologies that use existing wires or cable limit data rates to 10 Mbps. This may not be sufficient for large file transfers or video servers on a network.
If you use a network switch, you can mix old cable using HomePNA technology and new cable using 100 Mbps Ethernet on the same network. Each connection will operate at its designated speed. However, if you use a hub, all of the connections will be reduced to the speed of the slowest device connected to the hub.
When walls can't be fished, you have two alternatives: use surface raceway or run the cables outdoors. Most surface-mount raceway is made of plastic and is easy to work with. Decorative raceway can replace a baseboard. Raceway that simulates a cornice molding or chair rail is also available. When running cables horizontally outdoors, it's usually best to run the cable under the eaves of the house. And remember, indoor cable isn't rated for outdoor use.
When fishing walls, cut all of the holes for outlets at the same time. Fish all of the walls and leave a pull string in place. The pull string will be used when the cable pulling begins. Mount all of the raceway to these locations and install outlet boxes where required.
Some SMCs are designed to be surface-mounted. These units are great for retrofit applications. Surface-mount cabinets will generally use some type of surface-mount raceway to create a neat and professional appearance for the cable entering the SMC.
Once all of the walls have been fished and surface-mount raceway has been mounted, you can begin cable pulling. Just as in new construction, you should label the cables as you pull them. Retrofit projects are a good place to consider using the newer composite cables or the so-called “bundled structure cabling systems.”
The last step in the rough-in process for retrofit projects is the clean up. In a retrofit, the clean up is extremely important since the homeowners must live in the home while you're finishing your work and it should be completed promptly after cables are pulled and dressed.
Like it or not, as an HTI, you'll almost always be last in line to gain access to the wall cavity — in both new construction and retrofits — so you're going to have to learn to work with less elbow room than you may like. But careful planning and a little help from some tricks of the trade will make the process go a little more smoothly.
Dusthimer is publisher of Cisco Learning Institute Press, York, Pa.
Here's a set of steps that should make your project go more smoothly when working in a multi-level house.
While on the lower floor, use a sensor to pinpoint the two joists that you'll pull the cable through.
Next, cut a hole about 2 in. in diameter between the joists that you located in step 1, and measure the distance from the center of the hole to the outside wall parallel to the joists.
Go upstairs and measure the same distance from the same outside wall.
Pull back the carpet and drill a hole between the tack strip and the molding of the floor. Using a stop ring on the fishing chain, drop it so that it piles on top of the ceiling below.
Head back downstairs and open the ceiling and locate the pile of fishing chain.
Attach the fishing chain to about 10 ft of pull cord and attach the cable to the cord.
In the final step, return upstairs, and use the chain and pull cord to pull the cable or wire into position.