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.