Tuesday, February 14, 2012

Wall Plate Mounting System



Another decision you must make regarding your wall plates is how you will mount them to the wall. Three main systems, each with its own unique applications, are used to attach wall plates to a wall:
  • Outlet boxes
  • Cut-in plates
  • Surface-mount outlet boxes
The following sections describe each of these mounting systems and their various applications.

Outlet Boxes

The most common wall plate mounting in commercial applications is the outlet box, which is simply a plastic or metal box attached to a stud in a wall cavity. Outlet boxes have screw holes in them that allow a wall plate to be attached. Additionally, they usually have some provision (either nails or screws) that allows them to be attached to a stud. These outlet boxes, as their name suggests, are primarily used for electrical outlets, but they can also be used for telecommunications wiring because the wall plates share the same dimensions and mountings.
Plastic boxes are cheaper than metal ones and are usually found in residential or light commercial installations. Metal boxes are typically found in commercial applications and usually use a conduit of some kind to carry electrical or data cabling. Which you choose depends on the type of installation you are doing. Plastic boxes are fine for simple, residential Category 3 copper installations. However, if you want to install Category 5e or higher, you must be extremely careful with the wire so that you don't kink it or make any sharp bends in it. This is especially true for Category 6A UTP cables, which can be as large as 0.35. Make sure you use boxes that are designed for the cable that you will be using. Also, if you run your network cable before the drywall is installed (and in residential wiring with plastic boxes, you almost always have to), it is likely that the wires will be punctured or stripped during the drywall installation. Open-backed boxes are often installed to avoid bend-radius problems and to allow cable to be pushed back into the cavity and out of reach of the dry-wall installers' tools. If you can't find open-backed boxes, buy plastic boxes and cut the backs off with a saw.
Metal boxes can have the same problems, but these problems are minimized if the metal boxes are used with conduit—that is, a plastic or metal pipe that attaches to the box. In commercial installations, a metal box to be used for telecommunications wiring is attached to a stud. Conduit is run from the box to a 45-degree elbow that terminates in the airspace above a dropped ceiling. This installation technique is the most common wiring method in new commercial construction and is illustrated in Figure 1. This method allows you to run the telecommunications wire after the wallboard and ceiling have been installed, thus minimizing the chance of damage to the cable.
 
Figure 1: A common metal box with conduit, in a commercial installation

Cut-In Mounting

Outlet boxes work well as wall plate supports when you are able to access the studs during the construction of a building. But what type of wall plate mounting system do you use once the drywall is in place and you need to put a wall plate on that wall? In this case, you should use some kind of cut-in mounting hardware (also called remodeling orretrofit hardware), so named because you cut a hole in the drywall and place into it some kind of mounting box or plate that will support the wall plate. This type of mounting is used when you need to run a cable into a particular stud cavity of a finished wall.
Cut-in mountings fall into two different types: remodel boxes and cover-plate mounting brackets.
Remodel Boxes
Remodel boxes are simply plastic or metal boxes that mount to the hole in the drywall using screws or special friction fasteners. The main difference between remodel boxes and regular outlet boxes is that remodel boxes are slightly smaller and can only be mounted in existing walls. Some examples of remodel boxes are shown in Figure 2.
 
Figure 2: Examples of common remodel boxes
Installing a remodel box so that you can use it for data cabling is simple. Just follow these steps:
  1. Using the guidelines, determine the location of the new cabling wall plate. With a pencil, mark a line indicating the location for the top of the box.
  2. Using the hole template provided with the box, trace the outline of the hole to be cut onto the wall with a pencil or marker, keeping the top of the hole aligned with the mark you made in step 1. If no template is provided, use the box as a template by flipping the box over so the face is against the wall and tracing around the box.
  3. Using a drywall keyhole saw, cut out a hole, following the lines drawn using the template.
  4. Insert the remodel box into the hole you just cut. If the box won't go in easily, trim the sides of the hole with a razor blade or utility knife.
  5. Secure the box by either screwing the box to the drywall or by using the friction tabs. To use the friction tabs (if your box has them), just turn the screw attached to the tabs until the tabs are secured against the drywall.
Cover-Plate Mounting Brackets
The other type of cut-in mounting device for data cabling is the cover-plate mounting bracket. Also called a cheater bracket, this mounting bracket allows you to mount a wall plate directly to the wallboard without installing an outlet box. Figure 3 shows some examples of preinstalled cover-plate mounting brackets.
 
Figure 3: Cover-plate mounting bracket examples
These brackets are usually made of steel or aluminum and contain flexible tabs that you push into a precut hole in the drywall. The tabs fold over into the hole and hold the bracket securely to the drywall. Additionally, some brackets allow you to put a screw through both the front and the tabs on the back, thus increasing the bracket's hold on the drywall. Plastic models are becoming popular as well; these use tabs or ears that you turn to grip the drywall. Some also have ratchet-type gripping devices.
Figure 4 shows a cover-plate mounting bracket installed in a wall ready to accept a wall plate. Once the mounting bracket is installed, the data cable(s) can be pulled through the wall and terminated at the jacks for the wall plate, and the wall plate can be mounted to the bracket.
 
Figure 4: An installed cover-plate mounting bracket

Surface-Mount Outlet Boxes

The final type of wall plate mounting system is the surface-mount outlet box, which is used where it is not easy or possible to run the cable inside the wall (in concrete, mortar, or brick walls, for example). Cable is run in a surface-mount raceway (a round or flat conduit) to an outlet box mounted (either by adhesive or screws) on the surface of the wall. This arrangement is shown in Figure 5.
 
Figure 5: A surface-mount outlet box and conduit
The positive side to surface-mount outlet boxes is their flexibility—they can be placed just about anywhere. The downside is their appearance. Surface-mount installations, even when performed with the utmost care and workmanship, still look cheap and inelegant. But sometimes they are the only choice.

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