Relays and Contactors Module 030204a Flashcards

(49 cards)

1
Q

What are the THREE main parts of a relay?

Relays and Contactors ILM

A

Coil.
Core.
Armature.

Relays and Contactors ILM
Page 17

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2
Q

What is the purpose of laminations in relays and contactors?

Relays and Contactors ILM

A

Reduce affects of eddy currents.

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Page 22

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3
Q

What is the purpose of shading coils in relays and contactors?

Relays and Contactors ILM

A

Creates a magnetic flux out of phase with the magnetic flux of the main coil.
Reduces chattering.

Relays and Contactors ILM
Page 23

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4
Q

What are the THREE most used metals for relay contacts?

Relays and Contactors ILM

A

Silver.
Copper.
Cadmium.

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Page 25

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5
Q

List the Use, Advantage and Disadvantage of Silver Contacts.

Relays and Contactors ILM

A

Use: Lower voltage and current applications

Advantage: Considered Self-cleaning as silver oxide is conductive.

Disadvantage: Soft metal so it can easily weld together. Cannot be used in high current applications.

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Page 25

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6
Q

List the Use, Advantage and Disadvantage of Copper Contacts.

Relays and Contactors ILM

A

Use: High voltage and current applications.

Advantage: Can be used with higher spring pressures.

Disadvantage: Prone to pitting and oxidization. Cannot be used for frequent switching applications.

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Page 25

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7
Q

List the Use, Advantage and Disadvantage of Cadmium Contacts.

Relays and Contactors ILM

A

Use: High voltage and current applications as well as frequent switching under load conditions.

Advantage: Can withstand strong spring tension, has a longer contact life and maintains constant contact resistance.

Disadvantage: Does not conduct as well as silver.

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Page 25

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8
Q

What is Contact Bounce?

Relays and Contactors ILM

A

When contacts slam against each other with such force that they bounce open again. This causes additional arcing and reduces the lifespan of the contacts.

Relays and Contactors ILM
Page 27

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9
Q

What is the purpose of Contact Springs?

Relays and Contactors ILM

A

Used to absorb the impact of closing contacts.
Maintain pressure when the contacts are closed.

Relays and Contactors ILM
Page 28

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10
Q

What is the purpose of Armature Springs?

Relays and Contactors ILM

A

Used to quickly return the armature to the original state when the coil is de-energized.

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Page 29

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11
Q

What is the purpose of a curved contact design?

Relays and Contactors ILM

A

Helps reduce contact bounce.
Allows for self-cleaning.

Relays and Contactors ILM
Page 30

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12
Q

What are the advantages and disadvantages of bridge contacts?

Relays and Contactors ILM

A

Advantages: Good contact alignment, reduced arcing, self cleaning contacts.

Disadvantages: More complex and increase the size of the contactor enclosure.

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Page 31

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13
Q

What can happen if contact springs are too loose?

Relays and Contactors ILM

A

Will not maintain proper contact pressure which increases resistance and heat.

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Page 30

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14
Q

What can happen if contact springs are too tight?

Relays and Contactors ILM

A

Will not properly absorb the shock of contacts closing. Results in contact bounce and possibly contacts becoming welded together due to arcing.

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Page 30

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15
Q

What can happen if the armature spring is too loose?

Relays and Contactors ILM

A

Will not open the armature fast enough to safely de-energize a power circuit.

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Page 30

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16
Q

What can happen if the armature spring is too tight?

Relays and Contactors ILM

A

Magnetic field may not be strong enough to pull the armature closed which could result in the coil burning out.

Relays and Contactors ILM
Page 30

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17
Q

What percentage of voltage across a coil is needed to seal-in the armature?

Relays and Contactors ILM

A

85% of the rated voltage of the coil.

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Page 35

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18
Q

What percentage of voltage across a coil will cause the armature to drop-out?

Relays and Contactors ILM

A

Approximately 50% of the rated voltage of the coil.

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Page 35

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19
Q

Why happens to current when the armature seals against a coil and why?

Relays and Contactors ILM

A

Inductance increases due to no air gap which increases impedance.
Current decreases due to the increased impedance.

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Page 35

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20
Q

What can happen if a higher voltage is applied to a coil than what it is rated for?

Relays and Contactors ILM

A

Armature can snap in too quickly and damage the armature poles faces and contacts.
Can cause the coil windings to break down and coil burnout.

Relays and Contactors ILM
Page 36

21
Q

What is the maximum percentage of voltage that should be applied to a coil?

Relays and Contactors ILM

A

Never more than 110% of its rated voltage.

Relays and Contactors ILM
Page 36

22
Q

What can happen if a lower voltage is applied to a coil than needed?

Relays and Contactors ILM

A

Not enough magnetic flux to pull the armature closed causing a higher current and coil burnout.
Can also cause contact chattering resulting in contact pitting, carbon buildup and high contact resistance.

Relays and Contactors ILM
Page 36

23
Q

What are some reasons an armature may fail to drop out when the coil is de-energized?

Relays and Contactors ILM

A

Residual magnetism in the armature.
Contacts are welded together.
Jammed armature.

Relays and Contactors ILM
Page 38

24
Q

What is the main difference between a relay and a contactor?

Relays and Contactors ILM

A

Contactors are for higher current applications.

Relays and Contactors ILM
Page 3

25
What are the FOUR basic relay categories? Relays and Contactors ILM ## Footnote Relays and Contactors ILM
Power relays. Plug-in relays. Industrial control relays. Low-voltage lighting relays. ## Footnote Relays and Contactors ILM Page 4
26
What are power relays designed for? ## Footnote Relays and Contactors ILM
Small motors and heating applications that do not require frequent cycling. ## Footnote Relays and Contactors ILM Page 4
27
What is the maximum that contacts are rated for in power relays? Relays and Contactors ILM ## Footnote Relays and Contactors ILM
30 amps and 2 horsepower. ## Footnote Relays and Contactors ILM Page 4
28
What relay is an open-type with exposed contacts? ## Footnote Relays and Contactors ILM
Power relays. ## Footnote Relays and Contactors ILM Page 4
29
What are plug-in relays also referred to as? ## Footnote Relays and Contactors ILM
General-purpose relays. ## Footnote Relays and Contactors ILM Page 5
30
What type of relay can be replaced quickly without loosening wire terminals? ## Footnote Relays and Contactors ILM
Plug-in relays/General-purpose relays. ## Footnote Relays and Contactors ILM Page 5
31
What are plug-in relays rated for? ## Footnote Relays and Contactors ILM
Rated for up to 15 amps and small motor loads under 1/2 horsepower. Intended for control circuits. ## Footnote Relays and Contactors ILM Page 5
32
What are the two types of pins on plug-in relays? ## Footnote Relays and Contactors ILM
Tubular - often arranged in a circle. Spade - often arranged in rows and columns. ## Footnote Relays and Contactors ILM Page 5
33
How many pins are typically available for plug-in relays? ## Footnote Relays and Contactors ILM
5, 8, 11, or 14. ## Footnote Relays and Contactors ILM Page 5
34
How many pins are associated with each set of NO/NC contacts and coils on plug-in relays? ## Footnote Relays and Contactors ILM
Three pins for every set of NO/NC contacts Two to Three pins for every operating coil. ## Footnote Relays and Contactors ILM Page 5
35
What type of relay is a latching relay? ## Footnote Relays and Contactors ILM
Plug-in type. ## Footnote Relays and Contactors ILM Page 5
36
What is the purpose of Industrial Control Relays? ## Footnote Relays and Contactors ILM
Heavy-duty applications. ## Footnote Relays and Contactors ILM Page 6
37
What is the purpose of adder decks? ## Footnote Relays and Contactors ILM
Allows you to increase the amount of contacts for relays. ## Footnote Relays and Contactors ILM Page 6
38
What is the operating voltage of low-voltage lighting relays? ## Footnote Relays and Contactors ILM
30V or less. ## Footnote Relays and Contactors ILM Page 7
39
What does a contactor need to be combined with to be used as a motor starter? ## Footnote Relays and Contactors ILM
An overload device. ## Footnote Relays and Contactors ILM Page 8
40
What is a reversing contactor? ## Footnote Relays and Contactors ILM
Two non-reversing contactors with a mechanical and electrical interlock between them. ## Footnote Relays and Contactors ILM Page 9
41
What are mechanically held contactors often used for? ## Footnote Relays and Contactors ILM
Provide central lighting control of large lighting installations. ## Footnote Relays and Contactors ILM Page 11
42
How many coils does a mechanically held contactor have? ## Footnote Relays and Contactors ILM
Two coils. ## Footnote Relays and Contactors ILM Page 11
43
What are definite-purpose contactors controlled by? ## Footnote Relays and Contactors ILM
Automatic thermostat or manual push-button interface. ## Footnote Relays and Contactors ILM Page 11
44
What is the Form A contact arrangement? ## Footnote Relays and Contactors ILM
SPST-NO (Single-pole, single-throw normally open) ## Footnote Relays and Contactors ILM Page 14
45
What is the Form B contact arrangement? ## Footnote Relays and Contactors ILM
SPST-NC (Single-pole, single-throw normally closed) ## Footnote Relays and Contactors ILM Page 14
46
What is the Form C contact arrangement? ## Footnote Relays and Contactors ILM
SPDT (Single-pole double throw) ## Footnote Relays and Contactors ILM Page 14
47
What is the Form X contact arrangement? ## Footnote Relays and Contactors ILM
SPST-NO-DM (Single-pole, single-throw normally open double make (bridge contact)) ## Footnote Relays and Contactors ILM Page 14
48
What is the Form Y contact arrangement? ## Footnote Relays and Contactors ILM
SPST-NC-DB (Single-pole, single-throw normally closed double break (bridge contact)) ## Footnote Relays and Contactors ILM Page 14
49
What information can be found on a nameplate for a relay or contactor? ## Footnote Relays and Contactors ILM
Coil Ratings. Contact Ratings. Contact style and arrangement. Contact terminal numbering. ## Footnote Relays and Contactors ILM Page 13