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About Electric Switches
Electric switches, electronic switches or electrical
switches are devices used to connect or break an electrical circuit.
All switches consist of an operator, contacts and a switch mechanism.
The operator actuates switch operation. The contacts are made of low-resistance
metal and are used to make or break the electrical circuit. The switch
mechanism is linked to the operator and opens/closes the contacts. The
function of the switch is designated by the terms pole, throw and break.
Pole indicates how many circuits a switch is capable of controlling.
Throw refers to how many conductors or paths that a switch is able to
control. Break is a term that refers to the breaking or opening of a
circuit. The term “position” indicates how many stops a switch
will make between its extreme settings.
The two most basic switch devices, of which other mechanisms are simply
variations, are the slow-make, slow-break (AC base) and the quick-make,
quick-break (AC/DC base) mechanisms. The first device is basically a
teeter-totter or seesaw design. It is spring-loaded, requiring a very
positive force to close the contacts. The slowness of a slow-make, slow-break
device provides a slight time delay. This delay allows the AC current
wave to nearly instantaneously cycle to zero before the spark is extinguished.
Toggle switches, slide buttons, rocker switches or pushbutton switches
can operate the mechanism.
The operator of a quick-make, quick-break device is similar to a trigger
on a gun. It provides an irreversible action when tripped. The almost
instant action is suitable in DC applications, as the more rapidly the
contacts are separated, the sooner the arc of current is extinguished.
The mechanism of a quick-make, quick-break device uses a compression
type motor spring to provide the snap action. Quick-break, quick-make
mechanisms are smaller and more compact than slow-make, slow-break mechanisms
but are more costly. Quick-make, quick-break mechanisms also have self-wiping
contacts to prevent corrosive buildup.
Although the circuit configuration possibilities for electronic switches
are virtually endless, typical circuits include single-throw, double-throw
without center off, double-throw with center off and double-throw momentary
action with center off. The single-throw switch is the most basic circuit
with only two positions: on and off. Double-throw switches without an
off position in the center are referred to as ON-ON switches. These manual
electric switches are commonly used in selector applications (e.g. 6V
or 12V on a battery charger). Double-throw electric switches with a center
off position are three-position switches with two independent ON switches,
an example of which is the HI-OFF-LOW settings of a kitchen range hood
exhaust fan. Three-position double-throw electric switches with momentary
action use a spring loading action. As long as pressure is applied to
the actuator, the position will be maintained, making these electronic
switches operator-dependent.
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Types of Electric Switches
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have a plastic disk (cam) over which contoured surface a mechanical
follower moves, controlling the contacts. The cam is attached to and
rotated by a handle shaft.
- open or close the connections of two conductors
to a pair of separate circuits. DPDT switches, which usually have six
terminals, can be set to maintain contact, alternate contact or have
momentary contact.
- open or close the connection of a pair
of circuit conductors in a single circuit. DPST switches usually have
four terminals.
- are a set of small-sized ON-OFF switches. DIP
switches are used in place of jumpers and in such electronics as garage
door openers, personal computers and paintball marker electro-chips.
- change the flow of electric current.
-
are similar to safety switches, except they are manually operated. Enabling
switches are designed to protect workers in more hazardous environments
in which there is heavy machinery.
-
are activated by use of a fitting key. The key is turned to one of
several positions, triggering the switch.
-
are activated by turning a lever that is connected to a pivot point.
Lever switches typically have three positions.
-
are utilized in monitoring and for the control of machinery and industrial
equipment. Limit switches come in many different sizes and configurations.
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stay in the selected position when the handle is released.
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are used in applications that require compact mechanisms, such as handheld
equipment.
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are used for the positioning and control of industrial equipment and
machinery.
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convert pressure changes to electrical functions.
-
are so called due to their activation method, which is usually in the
form of a plunger that, when pushed down, opens or closes the switch.
The configurations of these mechanical switches can be single-pole single-throw
(SPST), single-pole double-throw (SPDT), double-pole single throw (DPST),
double-pole double throw (DPDT) or solid state.
-
feature two contact blades, called ferromagnetic reeds, which are encapsulated
in glass. The reeds close when exposed to a magnet.
- are electric switches that are activated by rocking the switch to one side.
-
are triggered when there is tension in the safety cable. Rope pull
switches provide safety and monitoring contacts in the printing,
food processing and pharmaceutical industries.
-
have contacts that are arranged in a full or partial circle, which
means the mechanism that selects the contact must be turned. Rotary
switches, which may be manual or automatic, are used in such applications
as automobile distributions or ignition switches.
-
feature integrated actuators, which serve to protect both equipment
and personnel. This is done by monitoring the positions of movable components.
- , also referred to as “three-way
switches,” open or close the connection of one conductor with
one of two other conductors. SPDT switches often have three terminals
and are sometimes used in pairs.
- , also called a “single-pole switches,”
open or close the connection of one conductor in a single circuit. SPST
switches usually have two terminals.
-
are designed to very quickly move their contacts from one location to
another. Mouse buttons and appliance settings use such switches.
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have only two positions. Light switches and the caps lock key on a computer
keyboard are examples of toggle switch applications.
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