Relays and Contactors

Question 1

What are the four categories of electromagnetic relays?

Answer 1

plug in, industrial, power, low voltage

Question 2

What are the two types of pins in plug in relays?

Answer 2

tubular, spade

Question 3

How many terminals would be associated with one NO/NC contact on a plug in relay?

Answer 3

three

Question 4

How many operating coils does a latching relay have?

Answer 4

one or two

Question 5

How can we increase the number of contacts that an industrial control relay operates?

Answer 5

we can install adder decks

Question 6

Which type of relay uses open-type exposed contacts?

Answer 6

power relay

Question 7

A relay has two sets of ratings for voltage and current. One set is for the _____ and the other is for the _____

Answer 7

contacts, coils

Question 8

What are the switching arrangements for Form C contacts?

Answer 8

SPDT

Question 9

What are the switching arrangements for Form A contacts?

Answer 9

SDST-NO

Question 10

What are the switching arrangements for Form X contacts?

Answer 10

SPST-NO-DM

Question 11

A relay’s rating may be classified according to which two agencies?

Answer 11

NEMA, IEC

Question 12

Are a contactor coil and its movable contacts physically linked?

Answer 12

no

they are electrical linked

Question 13

When are a set of normally open contacts in the open position?

Answer 13

when the circuit is de-energized

Question 14

What are the three main components of a contactor?

Answer 14

core, coil, armature

Question 15

Why do we laminate the iron or steel armature?

Answer 15

to reduce eddy currents

Question 16

What are installed to minimize chattering and its undesirable noise and heating effects?

Answer 16

shading coils

Question 17

What is a cause of chattering contacts?

Answer 17

undesirable heating

Question 18

What are the three different types of contact material?

Answer 18

copper, silver, cadmium

Question 19

Why can’t silver be used for high current application?

Answer 19

too soft

Question 20

Copper contacts are more prone to _____ and _____ than cadmium contacts

Answer 20

pitting, oxidization

Question 21

What is the best material for contacts to be used for a wide variety of application?

Answer 21

cadmium

Question 22

Why must relay contact springs provide the right tension?

Answer 22

to prevent contact bounce and provide good continuity

Question 23

What does the wiping action of contacts provide?

Answer 23

self-cleaning and confines the arcs to the tip of the contacts

Question 24

Incorrect spring tension can cause contacts to ______

Answer 24

overheat

Question 25

Bridge contacts help reduce _____ _____

Answer 25

electrical arcing

Question 26

How many places can bridge contacts open?

Answer 26

two

Question 27

What are two advantages of bridge contacts?

Answer 27

good contact alignment and provide a wiping action

Question 28

What is the seal in voltage?

Answer 28

the voltage at which the armature completes its full physical travel and the air gap in the magnetic circuit is closed

Question 29

At what percentage (approx.) is drop out voltage?

Answer 29

50%

Question 30

If material in a magnetic circuit changes from air to iron, the permeability of the core of the coil ____

Answer 30

increases

Question 31

When inductance increases, impedance _____

Answer 31

increases

Question 32

An increase in impedance causes the current to ____

Answer 32

drop

Question 33

What is the maximum voltage that can be applied to a coil (percentage)?

Answer 33

110% of rated voltage

Question 34

State three reasons for an armature to fail to drop out after it is de-energized

Answer 34

welded contacts, jammed armature, residual magnetism

Question 35

Can a lower than rated voltage applied to a coil damage it?

Answer 35

yes

Question 36

A low voltage condition causing contact chatter could result in ____ _____ developing at the contacts

Answer 36

resistance