RELAYS AND CONTACTORS (030204b)

Question 1

What are the two main classifications for motor control components

Answer 1

NEMA (National Electrical Manufacturers Association)

IEC (International Electrical Commission)

Question 2

What are contactors used with

Answer 2

Pilot control devices

Thermostats, push buttons float switches, pressure switches, limit switches

Question 3

Does a contactor contain overloads

Answer 3

No

Question 4

What is a creepage path

Answer 4

The shortest distance between two conductive parts

Question 5

True or false

A reversing contactor is an assembly of two non-reversing contactors with a mechanically and electrically interlock between them

Answer 5

True

Question 6

What is a non-reversing contactor

Answer 6

A single contactor with three main switching terminals

One per phase for a 3-phase supply

Question 7

What are mechanically interlocked contactors?

Answer 7

Two contactors mounted side-by-side in the control box. mechanical linkage. 

Question 8

What are definite purpose contactors designed for?

Answer 8

HVAC

Question 9

What information is displayed on a relay nameplate?

Answer 9

-Rating of the operating coil
-Ratings of the contacts controlled by the coil
-The style and arrangement of the contacts
-Contact terminal numbering

Question 10

True or false

A relay coil voltage rating must match the voltage of the control circuit is to be used in.

Answer 10

True

Question 11

What type of contacts do these characteristics describe?

-Double the typical # of contact points
-Parallel current paths
-Reduced contact resistance
-Increased switching reliability

Answer 11

Bifurcated Contacts

Question 12

What are the three basic components of a contactor

Answer 12

Core
Coil
Armature

Question 13

Typically ______ are used for control, circuits, and _______ are used for power circuits

Answer 13

Relays
Contactors

Question 14

What is the purpose of a shading coil?

Answer 14

The continual out-of-phase flux seals armature face to the core face and minimizes shattering and undesirable noise

Question 15

What are the three most common metals used for contact surfaces

Answer 15

Silver, copper, and cadmium

Question 16

What do you call it when contacts slam against each other and rebound creating a secondary arc

Answer 16

Contact bounce

Question 17

Why are the moving contacts in a relay typically spring-mounted

Answer 17

Absorb the impact of sudden closing

Question 18

What are 2 consequences of incorrect relay spring tension?

Answer 18

-Increase in resistance = heating of contacts
-Contact Bounce = excessive arcing, possibility of contacts welding together

Question 19

True or false

Plug-in relays are available with timing functions

Answer 19

True

Question 20

True or false

Plug-in relays can have 1 or 2 coils

Answer 20

True

Question 21

True or false

Relays can have a combination of NO & NC contacts

Answer 21

True

Question 22

SPST-NC contacts are Form ____

Answer 22

B

Question 23

For switching high current loads, are contactors or relays used

Answer 23

Contactors

Question 24

Where are shading coils located

Answer 24

In the pole face of the armature

Question 25

True or false

Copper would be the ideal contact material for frequent switching of high current

Answer 25

False

Question 26

Contact wiping results in _______ contact life

Answer 26

Longer

Question 27

Can a DC voltage be used to control a 120VAC load?

Answer 27

Yes

Question 28

What is the max voltage that can be applied to a 120V coil

Answer 28

132V (110%)

Question 29

What is Seal-in Voltage

Answer 29

The minimum voltage that can pull in the armature of a relay

Question 30

What % of the rated coil voltage is seal-in voltage

Answer 30

85%