It is often desirable in designing an electric wiring system to be able to control a

Chapter 21, Problem 40

(choose chapter or problem)

It is often desirable in designing an electric wiring system to be able to control a single appliance from two or more locations, for example, to control a lighting fixture from both the top and bottom of a stairwell. In home wiring systems, this type of controlis implemented with three-way and four-wayswitches. A three-way switch is a three-terminal,two-position switch, and a four-way switch is a fourterminal,two-position switch.The switches are shownschematically in Fig. P2.40(a), which illustrates athree-way switch, and P2.40(b), which illustrates afour-way switch.a) Show how two three-way switches can be connectedbetween a and b in the circuit inFig. P2.40(c) so that the lamp l can be turned ONor OFF from two locations.b) If the lamp (appliance) is to be controlled frommore than two locations, four-way switches areused in conjunction with two three-wayswitches. One four-way switch is required foreach location in excess of two. Show how onefour-way switch plus two three-way switches canbe connected between a and b in Fig. P2.40(c) tocontrol the lamp from three locations. (Hint:The four-way switch is placed between thethree-way switches.)