are classified by the number of poles. A one-pole switch can control only one circuit.
Two-pole switches can control two separate circuits at the same
time. For example, a large room may need two lighting circuits. If only one switch is needed, use a single two-pole switch.
Several two-pole switches can be ganged to control a number of circuits. This reduces the labor, switch, and box cost.
Many offices require two-level
lighting. Regulations designed to reduce energy consumption sometimes require two-level lighting in all office buildings.
Each four-lamp fluorescent fixture will have two lamps controlled from one switch and two lamps controlled by another switch
located immediately beside the first. When there are more than two circuits involved, two-pole switches can be used in the
same two-gang switch box.
Three-way switches allow switching a lighting circuit from two separate locations. For example, in a hall
you want lighting controlled from switches at either end. On a stairway you want lights controlled from both upstairs and
Four-way switches are used where three switches need control of the circuit. The four-way switch is connected into the
switching circuits between two three-way switches.
There are two types of switches with illuminated handles. One lights when the switch
is in the "ON" position. The other lights when the switch is in the "OFF" position. Either can be used
as a pilot light. But be sure you order the right switch. They're not interchangeable and can't be modified on site.
The switch that lights
when the switch is on is used where the switch and the fixture or appliance are in different rooms -- such as the light for
a storage room or closet.
The switch that lights when the switch is off is used in rooms that are normally dark when unlighted. When
the switch is on, the handle isn't illuminated.
Quiet (silent) switches are a good choice for better-quality homes and offices. You'll
hear these called mercury switches, but they may or may not be made with mercury contacts. Quiet switches come in voltages
Heavy duty "T"
rated switches are made for heavy loads. The circuit is closed by a contact armature that moves very fast to minimize arcing
when the switch changes position.
Decorative wiring devices are offered by some manufacturers. Unlike standard devices, decorative devices
are generally rectangular. The trim plate is designed to fit only a decorative style device. And note that trim plates made
by some manufacturers for decorative switches won't fit decorative duplex receptacles by the same manufacturer. That creates
a problem when placing a decorative switch and a decorative duplex receptacle in the same box.
Horsepower-rated switches are used
to control small motor loads, such as exhaust fans, where manual motor starters are not required. The motor has a built-in
Key-operated switches are common in public areas where lighting shouldn't be controlled by the public -- for example,
in a public restroom where the light has to be on while the building is open to the public. Key switches come with either
a simple stamped 2-prong key or a conventional lockset.
Duplex switches have two switches mounted in a housing shaped like a duplex outlet.
They can be wired to control two separate circuits or to control one circuit with two loads. Duplex switches can be used to
control two-level lighting in an office.
Momentary-contact switches provide current only for an instant. When not being activated, the switch is always
open. Momentary switches are commonly used to throw another switch like a lighting contactor that controls a large bank of
fluorescent lights. If the lighting contactor has a close and open set of coils, a momentary-center-off switch is used. The
contactor is closed when the momentary switch handle is lifted to the on position. When the switch handle is released, it
returns to the center position. To de-energize the lighting contactor, the momentary switch is pushed down to the off position.
Any time the momentary switch handle is released, it returns to the center position.
Maintain-contact switches are used when current is
to flow in both the on and off positions. There is a center off position. But the switch handle must be moved to that center
position. It doesn't return to center by just releasing the handle. One application for this type of switch is a conveyor
that can be operated in two directions but also has to be stopped when not in use. There are many other applications