No doubt you have seen lights (or electric appliances) controlled by two
or more
switches. Each switch is part of one
electric circuit
that can turn the light on or off, irrespective of the position of the
other switches. You often encounter this system in situations where it
is inconvenient to return to the place where you initially turned on a
light. For instance, the lighting in
hotel rooms needs to
be controlled at the entrance, as well as the bed.
How do electricians do this? What you need are 3-way switches to control the lighting. A 3-way switch has two
switch positions, connecting either (1) A to B, or (2) A to C (see diagram).
•----B •----B
/
/
A----• A----•
\
\
•----C •----C
(3) (3)
If the circuit requires 3 or more switches to control an electric
appliance, you need additional 4-way switches. These
switches also have two switch positions and connect either (1) A to D
and C to B, or (2) A to B and C to D. (see diagram).
A----• •----B A----•-----•----B
\ /
\ /
X
/ \
/ \
C----• •----D C----•-----•----D
(4) (4)
A circuit requiring two switches is built up from two 3-way switches as
follows:
S-----------*-----------|
|
|
•-------• |
/ \ |
/ \ |
S----• •----|
•-------•
(3) (3)
Where (S) is the power source, and (*) is a light fixture or
electric appliance (currently shown in the ON position).
A circuit requiring three switches has a similar configuration, but
an additional 4-way switch is added in between the two 3-way switches:
S------------------*------------------|
|
|
•-------• •-------• |
\ / \ |
\ / \ |
S----• X •----|
\ / \
\ / \
•-------• •-------•
(3) (4) (3)
Where (S) is the power source, and (*) is a light fixture or
electric appliance (currently shown in the ON position).
Additional controls can be built by installing additional 4-way switches in between
the two 3-way switches.