is possible to drill through the wall horizontally through several studs (if the operator is careful) and then pull the wires back through the holes to the openings.
The installation of an outside annunciator under the eave of a house with an extremely low pitch to the roof would cause several problems in getting wires to the outlet. With the flexible shaft, a hole can be drilled through the boxing, as shown in figure 8-14. As soon as the bit penetrates the boxing, it is pushed into the attic as far as it will go. A recovery grip is then attached to the bit, the wire or cable inserted, and then pulled backward toward the outlet opening. The outlet box and annunciator (horn, bell, etc.) are installed under the eave and the other end of the cable is connected to the alarm system. Also, because the flexible shaft is more rigid than the conventional fish tape, it will penetrate attic insulation if any exists.
Figure 8-13. - How wires must be routed when one uses conventional tools.
Figure 8-14. - Method of drilling a hole through boxing by using a flexible shaft.
If it becomes necessary to install wiring in an attic and run cable from this area to the basement, the installation can be greatly simplified by using a flexible shaft. First drill through the top plate into the wall cavity, making sure that the drilling is not being done above a window or doorway or any other obstruction, such as existing wiring, ductwork, and so forth. Once through the top plate, the drill motor is turned off and the bit is pushed into the cavity of the wall as far as it will go. If no fire stops are encountered, the bit is pulled back and an extension is attached to the shaft. With the extension installed, the bit is again lowered into the wall cavity until a fire stop is encountered. The bit is then positioned and used to drill through the wooden member. Once the wooden member is penetrated, the drill motor is again stopped and the bit is lowered further until the bottom plate is reached. Continue drilling through the bottom plate in the basement or crawl space. Fasten the appropriate recovery grip, insert the wire or cable, and pull up the wire with the flexible shaft. The drill motor should be reversed only when the bit is passing through one of the wooden members.
Those who use the flexible shaft device often are certain to discover many other useful techniques for installing wiring in existing structures.
Wire sizes for the majority of low-voltage systems range from No. 22 to No. 18 AWG. However, when larger-than-normal currents are required or when the distance between the outlets is long, it may be necessary to use wire sizes larger than specified to prevent excessive voltage drop. Voltage-drop calculations should be made to determine the correct wire size for a given application even on low-voltage circuits.
The wiring of an alarm system is installed like any other type of low-voltage system. The process consists of locating the outlets, furnishing a power supply, and finally interconnecting the components with the proper size and type of wire.
Most closed systems use two-wire No. 22 or No. 24 AWG conductors and are color-coded for identification. A No. 18 pair normally is adequate for connecting bells to controls if the run is 40 feet (12 m) or less. Many electricians, however, prefer to use No. 16 or even No. 14 cable.Continue Reading