Figure 5-34. - Single-pole switch circuit.
A single-pole switch is a one-blade, on-and-off switch that may be installed singly or in multiples of two or more in the same metal box. In wiring a single-pole switch, a general rule is a neutral conductor (white wire) should not be switched or used as one leg in a switch loop. This rule is easily followed in conduit systems but does not apply to armored and nonmetallic sheathed cable. Article 200-7 of the NEC contains the exception to this rule. Figure 5-34 shows a single-pole switch circuit using nonmetallic sheathed cable.
In a three-way switch circuit, you may turn a light on or off from either of two positions. The typical situation is one in which one switch is at the head of a stairway and the other at the foot. Figure 5-35 shows how the circuit functions.
Figure 5-35. - Three-way switch circuit.
Terminals A and A' are the common terminals, and switch operation connects them either to B or C and B' or C', respectively. Either switch will operate to close or open the circuit, turning the lights on or off.
By tracing the circuit in figure 5-35 from the source, you can see that the hot wire goes to the first switch, through the closed switch blade to the other switch by way of the traveler, and through the closed switch blade to the other switch by way of the traveler, and through this switch to the light. If the position of either of the switches is changed, the circuit is broken.
One or more four-way switches may be used with two three-way switches to provide control of a lamp from three or more different points. A four-way switch is an extension of a three-way circuit by the addition of a four-way switch in series with the two traveler wires. Figure 5-36, view A, shows how a four-way switch is used in combination with two three-way switches to control a lamp from three locations. By tracing this circuit from the source, you observe the hot wire connected to Switch C passing through Position 1, which is closed. The hot wire continues to Point 4 on the four-way switch (B). At this time the toggle on Switch B is in the UP position, and contact is made from Point 4 to Point 3. The hot wire continues on through the traveler to Switch A, and through Position 2 (which is closed) to the light.
Figure 5-36. - Four-way switch circuit.Continue Reading