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SWITCHES
-Bicol, Meryll Mae G.
ARC - 3101
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Switch
• a device that open or closed the circuitry in an electric circuit.• It is an electric component that can break an electric circuit
• Interrupting the current or diverting it from one conductor to another
• rated by current and voltage, duty, poles and throw, fusibility and enclosure
• switches are rated as 250v, 600v, or 5kv as required
The current rating is the amount of current that the switch can carry
continuously and interrupt safely. Switches intended for normal use in light and
power circuits are called general-use safety switches and are rated NO for
normal duty. Switches intended for frequent interrupting are rated HD for
heavy duty. Switches intended to be opened load only occasionally, such asservice switches are rated LD for light duty.
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Basic Structure of a Switch
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Manually Operated Electromechanical Device
It is the most familiar form of switch with one or more sets
of electrical contacts, which are connected to external circuits
Power Switching
When a switch is in the on state, its resistance is near zero
and very little power is dropped in the contacts; when a switch is in
the off state, its resistance is extremely high and even less power is
dropped in the contacts.
Mechanism of Switch
"toggle" (flip switch for continuous "on" / "off")
"momentary" (push-for "on" / push-for "off") type
A toggle switch in the
"on" position.
A momentary switch in
the “off” position.
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A switch may be directly manipulated by a human as a control signal to a
system, such as a computer keyboard button, or to control power flow in a circuit,
such as a light switch. Automatically operated switches can be used to control
the motions of machines, for example, to indicate that a garage door has reached its
full open position or that a machine tool is in a position to accept another work piece.
Switches may be Operated by Process Variables
• pressure
• temperature
• flow
• current
• voltage• force
They act as sensors in a process and used to automatically control a
system. For example, thermostat is a temperature-operated switch used to control a
heating process.
Relay
It is a switch operated by another electrical circuit.
Large switches may be remotely operated by a motor drive mechanism.
Some switches are used to isolate electric power from a system, providing a visible
point of isolation that can be padlocked if necessary to prevent accidental operation
of a machine during maintenance, or to prevent electric shock.
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Ideal Switch
• no voltage drop when closed
• no limits on voltage or current rating
• have zero rise time and fall time during state changes• change state without "bouncing" between on and off positions
• often used in circuit analysis as it greatly simplifies the system of equations to
be solved, however this can lead to a less accurate solution
Electrical switches - Top, left to right: circuit breaker, mercury switch, wafer
switch, DIP switch, surface mount switch, reed switch. Bottom, left to right:
wall switch (U.S. style), miniature toggle switch, in line switch, push-button
switch, rocker switch, microswitch.
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Two Conductive Pieces of Switch
• metal, called contacts, connected to an external circuit, that touch to
complete (make) the circuit, and separate to open (break) the circuit
• resistance to corrosion• hardness(resistance to abrasive wear)
• mechanical strength
• low cost
• low toxicity
• nonmetallic conductors, such as conductive plasctics are sometimes
used. To prevent the formation of insulating oxides, a minimum wettingcurrent may be specified for a given switch design
Contact Terminology
Two States of Set of Contacts
• "closed" meaning the contacts are touching and electricity can flow
between them
• "open" meaning the contacts are separated and the switch is non
conducting
• “make” - closure of contacts
• “break” - opening of contacts
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• normally open ("n.o." or "no") – contacts remain in one state unless
actuated until closed by operation of the switch
• normally closed("n.c." or "nc") - contacts remain in one state unless
opened by the switch action
• changeover switch - a switch with both types of contact• "make-before-break" ("MBB" or shorting)
- momentarily connect both circuits
• "break-before-make" ("BBM" or non-shorting)
- interrupts one circuit before closing the other
Switch Contact Variations • "poles" - number of separate circuits which are controlled by a switch at one time
For example, a "2-pole" switch has two separate identical sets of
contacts controlled by the same knob.
• "throws" - number of separate positions that the switch can adopt within a pole
Types of Throws Switch
• single-throw switch – has one pair of contacts that can either be closed or open
• double-throw switch
- has a contact that can be connected to either of two other contacts
• triple-throw switch
- has a contact which can be connected to one of three other contacts
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Poles and Schematics
Triple-pole single-throw (TPST or 3PST) knife
switchused to short the windings of a 3
phase wind turbine forbraking purposes.
Here the switch is shown in the openposition.
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Switches with larger numbers of poles or throws can be described byreplacing the "S" or "D" with a number (e.g. 3PST, 4PST, etc.) or in some
cases the letter "T" (for "triple") or "Q" (for "quadruple"). In the rest of this
article the terms SPST,SPDT and intermediate will be used to avoid the
ambiguity.
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Gas Plasma / Electric Arc
It is formed when the power being switched is sufficiently large, the electron flow across
opening switch contacts is sufficient to ionize the air molecules across the tiny gap between the
contacts as the switch is opened.
Plasma
It is low resistance and is able to sustain power flow, even with the separation distance
between the switch contacts steadily increasing. The plasma is also very hot and is capable of
eroding the metal surfaces of the switch contacts.
Puffer
This may be used to blow a sudden high velocity burst of gas across the switch contacts,
which rapidly extends the length of the arc to extinguish it quickly.
Inductive loads
When a strongly inductive load such as an electric motor is switched off, the current
cannot drop instantaneously to zero; a spark will jump across the opening contacts.
Incandescent loads
When turned on, an incandescent lamp draws a large inrush current of about ten times
the steady-state current; as the filament heats up, its resistance rises and the current decreases to
a steady-state value.
Wetting current
It is the minimum current needing to flow through a mechanical switch while it is operated
to break through any film of oxidation that may have been deposited on the switch contacts.
A
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Actuator
The moving part that applies the
operating force to the contacts and may be a
toggle or dolly, a rocker, a push-button or any
type of mechanical linkage.
Biased / Latching switches It maintains its state after being activated.
The momentary push-button switch is a type of biased
switch.
The most common type is a "push-to-make"
(or normally-open or NO) switch, which makes contact
when the button is pressed and breaks when the
button is released. Example: key of a computer
keyboard
Rotary switch It operates with a twisting motion of the operatinghandle with at least two positions. A rotary switch may
have multiple levels or "decks" in order to allow it to
control multiple circuits.
For example, a radio controlled overhead crane
may have a large multi-circuit rotary switch to transfer
hard-wired control signals from the local manual controlsin the cab to the outputs of the remote control receiver.
A three-deck stackedrotary switch.
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Toggle switchIt is a class of electrical switches that are
manually actuated by a mechanical lever, handle,
or rocking mechanism. It is a switch where a
definitive click is heard, is called a "positive on-off
switch".
Large toggle switch, depicted in circuit
"open" position, electrical contacts to left;
background is 1/4" square graph paper
Kill Switch / Emergency Stop / E-Stop
It is a safety mechanism used to shut off
a device in an emergency situation in which it
cannot be shut down in the usual manner.
Elevators often have a red two-way
button on the control panel which is either
marked "Emergency Stop" or "Run/Stop".
Normally, the button is in the "up" or unpushed
position, allowing the elevator to "run" in normal
service.
Emergency stop button - The
arrows indicate that the stop
button must be turned
to reset the switch before theequipment can be restarted.
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Load Control Switch
It is a remotely controlled relay that is
placed on home appliances which consume large
amounts of electricity, such as air conditioner units
and electric water heaters.
Membrane Switch
It is an electrical switch for turning a
circuit on and off.
Electronic membrane switches
Pull Switch
It is a switch that is actuated by means
of a chain or string.
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Push Switch
It is a momentary or non-latching switch
which causes a temporary change in the state of an
electrical circuit only while the switch is physicallyactuated.
Push-to-make switch Push-to-brake switch
electronic symbol electronic symbol
Time / Timer Switch
It operates an electric switch controlled by
the timing mechanism.
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Touch Switch
It is a type of switch that only has to be touched by an object to
operate.
Two Types
Capacitance switch needs only one electrode to function
Resistance switch needs two electrodes to be physically in
contact with something electrically conductive (for example a finger) to
operate.
Piezo Touch SwitchIt is based on mechanical bending of piezo ceramic, typically
constructed directly behind a surface.
Transfer Switch
It is an electrical switch that switches a load between two sources.
Centrifugal Switch
It is an electric switch that operates using the centrifugal
force created from a rotating shaft, most commonly that of an electric
motor or gasoline engine.
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Fireman Switch
It is a specialized switch disconnector /
isolator.
Switch used to shut off petrol pumps
at a petrol station in the event of a fire
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Classification of Switches •General Use Switch
intended for use in the general distribution and branch circuit rated in
amperes. It is capable of interrupting the rated current at a rated voltage.
•General Use Snap Switch
is a form of general use switch installed in flush device boxes or an
outlet box cover.•AC Geneial Use Snap Switch
•AC - DC General Use Switch
•Isolating Switch
Intended for isolating an electric circuit from the source of power. Switch
used to shut off petrol pumps at a petrol station in the event of a fire
•Motor Circuit Switch
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Alternate and Momentary
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N/O and N/C
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Lever Positions and Circuits
(ON) is momentary
Note: There is a distinction between “throw”and “position”.
Among two position switches there are single throw ON-NONE-
OFF and double throw ON-NONE-ON.
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Isolated Circuits for Illumination
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Types of Terminals
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Mounting Options
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Types of Actuators
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Typical Heavy Duty (Hd), 3 Pole Fusible Switch In Industrial Type Nema Enclosure
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Unless otherwise noted, a switch is assumed to be single throw.
Since the NEC states generally that the grounded neutral conductor
of a circuit should not be broken, most switches carry the neutral
through unbroken, by means of a solid link within the switch. Thisgives· rise to the term Solid Neutral ISNI Switch. Switches are
available in 1, 2, 3, 4 and 5-pole construction. Poles are indicated by
a "P"; thus 3-pole is written "3P", and so on. A switch may be
constructed with or without provision for fusing. If provided, the switch
is fusible; if not, the switch is nonfusible.
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Modern Electrical Switches
wireless switchesluxurious coverplates
minimalist
sleek architecture
cutting edge technology
infinite interior decor combinations
smooth and glossy mirror finish
exotic stingray leather (galuchat)
classic woven metal
super-soft electronic push-buttons/ touchplates
ergonomically designed
sophisticated
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Yellow Light Switch
This concept has a map displaying the
location of lights in your home indicated by light
bulb icons; pressing the icons turns on thecorresponding lights.
Revolving Light Switch
"Rotate the power switch and the
overhead lamp progressively opens to show the
light."
'Turn Me On' Light Switch
A cool switch design by Chris Haines
that requires you to breathe hard into its ear
hole in order to illuminate your room.
'Tio' Light Switch System
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Tio Light Switch System
It’s an interesting design from Tim
Holley, that gives kids a visual reminder of how
much energy they used by leaving the lights on.
Off Light Switch Hook
This cool hook switch comes from
electrical engineer Scott Amron, that gives extra
utility to a normal light switch in order to add a
real incentive to keep it switched "off" as often as
possible.
Hidden Light Switch
If you have a hidden door this is a cool
option, if not you can use it to turn on and off
the lights in your room.
Cubic Switchplate
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p
It creates an illusion of a three
dimensional cube-shaped light box, without the
need of taking up anymore real estate than a
normal flat switch.
Coin Light Switch
"A very simple modification to astandard electrical coverplate."
Berker Switches
These glittery and stylish switches
have been made using Swarovski crystals;
behind the crystal there exists an optical system
that also controls other items in the house.
Sentido Switches
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Sentido Switches
It works using a patented multi-touch
technology for a multiple keypress. "By touching
more than one area simultaneously, an extra comfort
function is activated. This can be used to switch allthe lights in the room on or off in a single movement
instead of multiple movements”.
Green Light Switches
These rotative
light switch designs'
display negative and
positive signals that will
represent the use of
energy.
Sexy and Sleek Switch
Mona Touch Sensitive
Push In Disappearing Outlet
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Push-In Disappearing Outlet
Modern Toggle
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