Suppose, now, that you want to turn the light off at the four-way switch (B). By putting the toggle in the OFF (down) position, you change the switch blades from Points 1 to 2 and 3 to 4 to Points 1 to 4 and 2 to 3. (See fig. 5-36, view B.) If you now retrace the circuit from Switch B to Switch A, you will find that it goes from Point 4 to Point 1 on Switch B and through the traveler to Switch A to Point 1 where the circuit is broken by the blade being in the open position.
Note that three- and four-way switches may be used as single-pole switches, and four-way switches may be used as three-way switches. However, three- and four- way switches are usually larger than single-pole switches and take up more box room. The size of a switch depends on its ampacity (rated maximum amperage). The ampacity and maximum allowable voltage are stamped on the switch and must be considered when you order equipment for the job.
Remote control wiring provides a method of controlling standard voltage devices through the use of low voltage. They consists of relays, low-voltage switches, and transformers. A low-voltage conductor cable is used instead of conduit or Romex. Low-voltage wire is available as three, four, and multiple conductor cables. Multiple conductors are color coded to identify them. Roughing in a remote control wiring system uses many of the wiring techniques used with nonmetallic cables.
Remote control relays have two coils (on or off) with a common center tap. The use of two coils allows the relay plunger to be moved positively in either direction without the use of springs. When a push button (switch) is turned ON, current will pass through the ON coil and cause the movable core to shift into the ON position. The contacts are closed in the load circuit and the light goes on. The same happens when the OFF button is depressed. The current is passed through the OFF coil and the core moves. The contacts open and power to the light is turned off. The relay will maintain this position until the push button again energizes the ON coil. These relays are capable of controlling 20 amperes of lighting or inductive loads at 110 or 277 volts ac. Relays can be mounted individually in junction boxes as shown in fig, 5-37, or several may be mounted in a centrally located cabinet.
Transformers in a remote control system reduce 120-volt line voltage to 24 volts to provide power in the switching/relay circuit. Wherever transformers are located, they must be accessible and they must be kept from excessive heat. They are sized according to the number of relays they will power.
Figure 5-37. - Low-voltage relay and transformer.
In the low-voltage system, as many switches as are required can be installed for any given light, or a master switch can be installed to turn on as many as eight lights simultaneously. There is no necessity for three-way or four-way switches because the switches are connected in parallel.
As a CE, you will be called upon to install all types of wiring systems. Unlike the electricians in civilian life who often specialize in the installation of specific types, you have to be able to install any type. In most locations you will have to install wiring systems that require the added protection provided by conduit. Conduits are of various types, such as rigid, flexible,
intermediate metal, PVC, and electrical metallic tubing (thin-wall or EMT). As you read this section, you should become familiar with the different ways of bending, cutting, and threading; the fittings used; and the different locations where they may be used.
The use of rigid conduit involves a good deal of cutting and threading of lengths. It is best to cut with a hacksaw or special conduit cutter. An ordinary
Figure 5-38. - Hacksaw blades, teeth per inch, for different types of conduit.Continue Reading