Figure 8-4. - Wire the shunt lock switch to the magnetic contacts as shown.

the magnet unit is mounted on the door or window (moving part) itself. The two units should be positioned so that the magnet is close to and parallel with the switch when the door or window is closed. This keeps the shunt lock actuated, but opening the door or window moves the magnet away and releases the switch mechanism.

As long as the faces of the switch and magnet are parallel and in close proximity when the door or window is closed, they may be oriented side-to-side, top-to-top, or top-to-side. Mounting spacers may be used under the units if necessary to improve their alignment and proximity.

Terminal covers are available for most makes of door contacts to give the installation a more finished look and also to protect the terminal connections against tampering.

The wiring of any alarm system is installed like any other type of low-voltage signal system; that is, one must locate the outlets, furnish a power supply. and finally interconnect the components with the proper size and type wire.

ALARM SYSTEMS INSTALLED IN EXISTING BUILDINGS

Many changes and advances in developing complete security/alarm systems for building operation and protection have taken place in the past few years. Numerous existing buildings are currently having security and fire-alarm systems installed either to replace their obsolete systems or to provide protection they never had.

The materials used for installing a complete alarm system in an existing building are essentially the same as those used in new structures. However, the methods used to install the equipment and related wiring can vary tremendously and require a great deal of skill and ingenuity. Each structure is unique.

When concealed wiring is to be installed in a finished existing building. the installation must be planned so that the Least amount of cutting and patching is necessary. In most cases, this means giving special consideration to the routing of conductors. Unlike the wiring of a new building where the installer would try to conserve as much material as possible, the amount of material used (within reason) is secondary in existing buildings. The main objective in security/fire-equipment installations in existing buildings is to install the wiring in the least amount of time with the least amount of cutting and patching of the existing finishes of the building.

Before any actual work on an existing building is started, the contractor or the installers should make a complete survey of the existing conditions in the areas where the security system will be installed. If the majority of the work can be done in exposed areas (as in an unfinished basement or attic), the job will be relatively simple. On the other hand, if most of the wiring must be concealed in finished areas, there are many problems to be solved. The initial survey of the building should determine the following:

1. The best location for the alarm control panel.

2. The type of construction used for the exterior and interior walls, ceilings, floors, and so forth.

3. The location of any chases that may be used for routing the conductors and the location of closets, especially those located one above the other for possible use in fishing wires.

4. The material used for wall and ceiling finishes - plaster, drywall, paneling, and so forth.

5. Location of moldings, baseboards, and so forth, that may be removed to hide conductors.

6. Location of decorations or other parts of the building structure that cannot be disturbed.

7. Location of any abandoned electrical raceways that new alarm system wires might be fished into. Do not overlook similar possibilities. For example, an old abandoned gas line can be used to fish security-system wires in an old building.

8. The location of all doors and windows, coal chutes, and similar access areas to the inside of the building.

As indicated previously, the most difficult task in running wires in existing buildings is the installation of concealed wiring in finished areas with no unfinished areas or access to them. In cases like these. the work is usually performed in one of two ways. First by deliberately cutting the finished work so that the new wiring can be installed. Of course. these damaged 8-4