Understanding basic AC control equipment 209

Question 1

The NEMA 7 enclosure is designed for use

Answer 1

where flammable gases or vapors may be present

Question 2

In the ______ mechanism, the hinged armature pivots to the sealed-in position.

Answer 2

Clapper

Question 3

The shading coil reduces which of the following in the armature?

Answer 3

Vibration

Question 4

The minimum potential diference that will cause the armature to seat against the pole faces of a relay coil is called the ____ voltage

Answer 4

Seal in

Question 5

Which of the following is NOT the result of the potential difference across the coil being too great?

Answer 5

Reduced magnetic force

Question 6

When appied to pushbultons, the terms standard duty and heavy duty apply only to the

Answer 6

amount of current the pushbutton contacts can carry

Question 7

A NEMA-type 1B flush-mounted station requires a

Answer 7

4 11/6 in. single outlet box

Question 8

NEMA-type 7-9 pushbutton stations for hazardous locations are suitable for all of the following locations EXCEPT

Answer 8

corrosive fumes or liquids

Question 9

When only one START STOP station is used with several emergency STOP buttons at different
locations, the STOP stations are wired

Answer 9

in series

Question 10

Which of the following are designed for only ac use?

Answer 10

Joy-stick operators

Question 11

The purpose of the actuator in a precision snapswich is

Answer 11

transmit force from the outside

Question 12

The temperalure that develops inside a swich under operating condions depends on al of ti
following EXCEPT the _____ current.

Answer 12

pulse

Question 13

When a remote cable actuator is used, the switch is mounted

Answer 13

where space permits

Question 14

When a plug in swich needs replacing. which is replaced?

Answer 14

Only the plug-in portion

Question 15

When should a mercury swich be replaced?

Answer 15

When the mercury strings out or breaks up into pools

Question 16

A ______ switch is used for changing a control circuit from one sequence to another.

Answer 16

Transfer

Question 17

Plugging switches can operate

Answer 17

both A and B

Question 18

Which kind of swich is clastied according to the kind of liquid or gas being measured?

Answer 18

Mechanical Pressure

Question 19

Capilay tube, direct immersion, and thermostat are kinds ___ of

Answer 19

temperature control

Question 20

Float swiches are used for controlin al of the following EXCEPT

Answer 20

temperature-maintaining equipment

Question 21

Typical time delay relays are normally used in applicalions that

Answer 21

do not often need changes in time settings

Question 22

In the multiple circuit timer, each set of timer contacts opens or closes according to

Answer 22

its cam setting

Question 23

What type of timer has only two cams?

Answer 23

Percentage

Question 24

If a counter is to be operated from an ac source, a _____ must be used with it.

Answer 24

rectifier

Question 25

revolution counter is used where a machine cannot be controlled

Answer 25

by time

Question 26

The displayed contacts are data.

Answer 26

double-make

Question 27

An undercurrent relay functions when the current reaches a(n)

Answer 27

lower limit

Question 28

The voltage sensing relay requires a

Answer 28

temperature-compensating network

Question 29

The oulput relay of a three phase sequence sensing relay de energizes when the

Answer 29

phase relationship is other than A-B-C

Question 30

What is the maximum vollage for a NEMA Class B industrial ac relay?

Answer 30

600 V

Question 31

Combustible dusts are Class _____ hazardous material

Answer 31

ll

Question 32

All of the flowing are potential sources of ignition EXCEPT

Answer 32

aluminum tools dropped on a steel surface

Question 33

Industrial control equipment located in Class 1, Division l areas

Answer 33

has all arcing parts immersed under 6 in. of oil

Question 34

In hazardous locations, where the conduit enters an enclosure housing arcing high- temperature equipment, a seal must be within________ in. of the enclosure it isolates.

Answer 34

18

Question 35

The main disadvantage of mineral insulated (MI)cable is its

Answer 35

tendency to attract moisture

Question 36

Atter the proper speed lip top (PSF) ercut has been set on a synchronous motor control unt, the setting can be cleared by a signal from the

Answer 36

pole slip (SPL) circuit

Question 37

Eight automatic sequence decelerating relays are required in a multispeed starter having ______ speeds

Answer 37

8

Question 38

An automatic autotransformer starter for a large induction motor begins by applying _____ line voltage to the motor.

Answer 38

less than full

Question 39

Part winding starters are generally used with motors having _____ connected windings.

Answer 39

delta

Question 40

The open circuit transition della starter has all of the folwing EXCEPT

Answer 40

a set of resistors

Question 41

Size ______starters are the largest size that can be accommodated by MCCs with drawout construction.

Answer 41

4

Question 42

The NEMA 12 endosure

Answer 42

has gaskets on all doors, cover and bottom plates, and around operating mechanisms

Question 43

Tin plated copper busbars are recommended for use in

Answer 43

corrosive environments

Question 44

A location for an MC needs to be all of the following EXCEPT

Answer 44

air-conditioned

Question 45

It work is required on the secondary circuis of an MC curent transformer afer they have been energized, the secondaries must be

Answer 45

short-circuited

Question 46

The end barriers on 600 V terminal blocks are ______ than those on 300 V blocks.

Answer 46

thicker and higher

Question 47

What type of wing terminals should be used where viration poses a threat of breakage

Answer 47

Insulated

Question 48

A specialy coaled steel spring is required for connecting

Answer 48

aluminum-to-aluminum wire

Question 49

A connector with no mark is for

Answer 49

copper conductors only

Question 50

When a panel is assembled, a plastic wiring duct may be

Answer 50

used to avoid the problems of laced wire