building utilities switches

7/29/2019 Building Utilities Switches

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SWITCHES

-Bicol, Meryll Mae G.

ARC - 3101



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.



Basic Structure of a Switch



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.



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.



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.



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



• 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



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.



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.



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



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.



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.



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.



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.



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.



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



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



Alternate and Momentary



N/O and N/C



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.



Isolated Circuits for Illumination



Types of Terminals



Mounting Options



Types of Actuators



Typical Heavy Duty (Hd), 3 Pole Fusible Switch In Industrial Type Nema Enclosure



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.



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



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



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



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



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



Push-In Disappearing Outlet

Modern Toggle

building utilities switches

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