Planning a Home Communications System

One thing that sets the modern digital home apart is an advanced communications system. Want to talk to someone on the other side of the house? A public address system allows instant and convenient communication with anyone in any room in your home. As you plan your communications system, it makes sense to design it around your other multimedia systems. Can you incorporate the public address system into your speakers? Would you like to add video features or music to the intercom installations? These are just a couple of considerations.

Selecting locations

Deciding what you want included in an intercom system and then wiring the home to accommodate the system is a basic step-by-step process:

1. Decide which rooms will have intercoms.

2. Select intercom units with sufficient capabilities to meet your needs.

3. Draw a wiring map.

4. Wire the house per the intercom manufacturer's instructions.

Keep in mind some basic rules and tips when wiring for intercom systems:

• You don't have to install an outlet box if you're only pre-wiring for a possible future expansion; simply get the wire in the wall cavity behind the drywall where you can later install a low voltage (LV) ring to accommodate the equipment.

• The rough in is generally done just inside the room next to the door. The installation height should be 5 feet above the finished floor.

• Don't run Cat 5 or 6 wires directly alongside wires for the electric power system. When two energized conductors are placed next to each other, a charge difference and electric field exists between them.

Ground loops can also cause interference with sound quality. All grounds should be connected to one grounding point. This ground point should be common with (meaning connected to) the electrical service ground. Once an item is grounded, it should not be grounded at another point or through another system.

• If you want stereo sound in a room, run additional wires to the wall or ceiling speaker locations.

• An alternative to pre-wiring a house is to provide an easy method for getting wires to future installation areas. You have a couple of options:

• Run conduit to those areas. In the case of a first floor over a basement, install a short piece from an electrical box through the floor into the basement, if the basement is to remain unfinished.

• Run conduit to some other accessible location, such as the attic. Fasten the conduit to the stud and mark it on the blueprint.

The diagram shown in Figure 1 is an example layout of a voice intercom system with auxiliary input and stereo sound. The manufacturer's recommended cable for wiring this system is Cat 5, and Cat 6 could be used as an upgrade.

Choosing wire

If you plan to pre-wire, how can you match the current carrying capacity of the wire to a future system? A number of intercom systems recommend using 16 or 18 AWG wire, but most future systems will probably use Cat 5 or Cat 6 wire. These systems send a higher voltage to the remote wall units; Cat 6 wire has about double the resistance of 18 AWG wire. You may have some line losses with Cat 6 wire on these systems, but they are generally insignificant.

Selecting amplifiers and speakers

Amplifiers, or amps, help provide adequate power to speakers. Like speakers, amplifiers usually have a wattage rating, but about half of that wattage is lost inside the amp. This means that the amplifier capacity can be twice as large as the speaker loads connected to it. The amp's purpose is to simply bring the volume up to the natural level of the instruments originally used to create the music, including the human voice. If the amp-and-speaker combination is too weak to reach equity, the instrument's full fidelity sound is impossible. Having to crank the controls to the max distorts the sound.

Selecting amps with a full frequency range of 20 to 20,000 cycles per second allows hearing of the harmonics and overtones of bells and stringed instruments.

Choosing intercom components

You have many intercom system and component brands from which to choose. A typical home intercom system can accommodate up to six remote speaker locations and chimes from three doors. If you install an electric door strike on your front door, you can unlock the door for identified visitors from the master station and use the intercom to tell them to enter the house.

In addition to a voice intercom, you can have a video intercom. Video intercom systems use a small camera in the intercom unit to monitor any room on the system. They aren't complicated to wire: just four-conductor 18 AWG wire. You may find it advantageous to see who's ringing the doorbell before you remotely unlock it, or you may wish to see what the kids are up to.