EEM401 Professional Aspects of Electrical Engineering - Contactors & Relays

8/9/2019 EEM401 Professional Aspects of Electrical Engineering - Contactors & Relays

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Switches & Relays

Osman Glercan

16169230356


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What is switch?

A switch is an electrical component that

can break an electrical circuit

Switches are highly varied based on theirintended utility.

A pair of contacts is said to be "closed"

when current can flow one to the other.

The termspole and throware also used to

describe switch contact variations.


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Some of Switch Types


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Electronics specification and

abbreviation SPST: Single pole, single throw SPDT: Single pole, double throw

SPCO SPTT, c.o. : Similar to SPDT.Some suppliers use SPCO/SPTTfor

switches with a stable off position in the

centre and SPDTfor those without

DPST: Double pole, single throw

DPDT: Double pole, double throw

DPCO: Double pole changeover

orDouble pole, centre off


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Dimmer Switches

Any standard single-pole switchcan be replaced with a dimmer,as long as the switch is of

adequate size.D

immerswitches have larger bodies thatstandard switches. They alsogenerate a small amount of heatthat must dissipate. For thesereasons, dimmers should not beinstalled in undersized electricalboxes or in boxes that arecrowded with circuit wires.Always follow themanufacturers specifications forinstallation.


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Double Switch

Separate-circuit wiring

Four black wires areattached to the

switch Feed wires from thepower source areattached to the sideof switch that has a

connecting tab, andthe connecting tab isremoved


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Pilot-light Switches

A pilot-light switch has abuilt-in bulb that glowswhen power flowsthrough the switch to alight fixture or appliance

Pilot- light switchesoften are installed for

convenience if a lightfixture or appliancecannot be seen fromthe switch location


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Timer Switches

Timer switches havean electricallypowered control dialthat can be set to turnlights on and offautomatically onceeach day

They are commonlyused to controloutdoor light fixtures


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Time-delay Switches

A time-delay switch hasa spring-driven dial thatis wound by hand

The dial can be set toturn off a light fixtureafter a delay rangingfrom I to 60 minutes

Time-delay switchesoften are used forexhaust fans, electricspace heaters, ventfans, and heat lamps


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Automatic Switches

An automatic switch

uses a narrow infrared

beam to detectmovement When a hand passes

within a few inches ofthe beam, an electronic

signal turns the switchon or off

Some automaticswitches have a manualdimming feature


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Automatic Switches

Automatic switches can

be installed wherever a

standard single-pole

switch is used Automatic switches are

especially convenient for

children and persons with

disabilities.

Automatic switchesrequire no neutral wireconnections

For this reason, anautomatic switch can beinstalled in a switch boxcontaining either one ortwo cables

The wire leads on theswitch are connected tohot circuit wires with wireconnectors


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Motion-sensor Security Switches

A motion-sensor switchuses a wide-angle infra-red beam to detectmovement over a largearea

Turns on a light fixtureautomatically

A time-delay featureturns off lights aftermovement stops


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Motion-sensor Security Switches

Most motion-sensorswitches have anoverride feature thatallows the switch to beoperated manually

Better switches includeadjustable sensitivitycontrol and a

Variable time-delayshutoff control.

Motion-sensor switchesrequire no neutral wireconnections

They can be installed inswitch boxes containingeither one or two cables

The wire leads on theswitch are connected to

hot circuit wires with wireconnectors


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Programmable Switches

Programmable

switches represent

the latest in switchdesign

They have digital

controls and

Can provide four on-off cycles each day


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ContactorsContactors

Contactors are relays that switch high

current loads a.k.a magnetic starters


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Contactors

A Contactoris a control devicethat uses a small controlcurrent to energize or de-energize the load connectedto it.

Abouts:

A contactor has a frame,plunger, and a solenoid coil.

The action of the plunger isused to close (or open) setsof contacts.

A contactor does not include

overload protection. The closing of the contacts

allows electrical devices to becontrolled from remotelocations.


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Relay Timers

ON Delay

OFF Delay


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Wired ON Delay

1. Energy appliedto power rails

X1 X2OFF

NC

NO

ON

1


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Wired ON Delay - NCTO

1. Energy applied topower rails

2. Start PB is pressed- Coil is energized

- Holding contact close- Timer contact stays

closed, lamp stays on.

- Count begins (5 sec)

2

X1 X2ON

NC

NC

ON


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Wired ON Delay - NCTO

3. Timer count ends- Coil is still energized

- Timer contact open

- lamp goes off.

4. Timer contacts remainopen until the coil is de-energized3

X1 X2ON

NO

NC

OFF

The Normally Closed contact will take 5 seconds To Open when the coil is energized.


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ON Delay - NOTC

1. Power is applied

to rails

X1 X2

The Normally Open contact will take 5 seconds To Close when the coil is energized.

OFF

NO OFF

1


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ON Delay - NOTC

2. Start PB is pressed

Coil energizes

Holding contacts

close

Timer contacts stay

open

Lamp stays off

Counter starts to

count (5 sec)

X1 X2


ON

NC

OFF

2


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ON Delay - NOTC

3. Counter finishes count

Coil stays energized

Timer contacts close

Lamp goes on

4. Timer contacts will

open when relay coil

is de-energized.

X1 X2


ON

NC

ON

3

NC


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OFF Delay - NCTC

1. Power is applied to

rails

2. Coil is off, contacts are

closed, lamp is on

The timer contacts will close 5 seconds after the coil is de-energized


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OFF Delay - NCTC

3. Start PB is pressed

4. Timer contacts open

5. Counter will start to

count only when coil is

de-energized.


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OFF Delay - NOTO

1. Power is applied to

rails

2. Coil is off, contacts are

closed, lamp is on


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OFF Delay - NOTO

3. Start is pressed.

4. Contacts close, lamp on

5. Counter only starts when

coil is de-energize

Documents

EEM401 Professional Aspects of Electrical Engineering - Contactors & Relays