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Level 2 Electrical, Canada > Motor Control > Flashcards

Motor Control Flashcards

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1
Q

Define a contactor

A

An electro mechanical device that opens and closes when the coil is energized

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2
Q

What two devices are found in a contactor?

A

A coil, and contacts

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3
Q

What three devices are found in a starter?

A

A coil, contacts, and OLR

Coil and contacts are ‘the contractor’

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4
Q

What is LVP and UVP and it’s purpose?

A

Low voltage protection, under voltage protection

Prevents machinery from restarting without pushing start button. Safety purpose.

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5
Q

What does N.C and N.O. Mean?

A

Normally closed - energized closed, denergized open
Normally open - denergized open, energized closed

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6
Q

What is overcurrent protection?

A

Fuses, breakers, devices that trip when current above its normal path is detected

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7
Q

What is overload protection?

A

Heater relays

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8
Q

What is 3 wire control?

A

LVP / UVP

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9
Q

What is a 2 wire control circuit?

A

LVR. Restarts equipment without pressing start

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10
Q

What is a power circuit?

A

Current path to motor

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11
Q

What are other names for holding contacts?

A

Seal in contact, maintaining contact.

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12
Q

Device that prevents chattering in coils

A

Shading coils

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13
Q

What are three common types of manual motor starters?

A

Toggle switch, push button start, drum switch

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14
Q

Three ratings found on manual motor starters

A

Voltage, amperage, horsepower

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15
Q

Drum switch ratings

A

1.5hp @ 120V, 3hp @ 240V

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16
Q

Which AC motor starter does not have overload protection?

A

Drum switch

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17
Q

What type of rating do contacts of manual motor starter have?

A

Horsepower

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18
Q

Why does a manual motor starter for a 240V motor have two power contacts?

A

For each ungrounded conductor

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19
Q

What problem can occur if a starter is constantly being reset?

A

Overloads will wear out and will cause nuisance trips

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20
Q

Heater selection for motors is based on what?

A

Full load current

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21
Q

Typical inrush current is approximately how large?

A

3-6 times normal running current

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22
Q

What is a drum switch used for?

A

Manually control speed, change motor direction.

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23
Q

What happens when a motor overload occurs?

A

Like current increases, heater elements warm, heater trips the O.L contacts and stops motor.

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24
Q

In the control circuit, what function does the NC contact have?

A

OLR, ectronical interlock

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25
Q

What does “full voltage control” mean?

A

Line voltage for control circuit

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26
Q

How do you change the direction of a motor?

A

Interchange any two leads of the motor

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27
Q

Difference between jogging and inching

A

Jogging is a momentary connection to full line voltage
Inching is a momentary connection to reduced line voltage

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28
Q

Over current protection protects the _________ and overload protection protects the _________

A

Conductors, equipment/motor

29
Q

Overloads should trip at ___% to _____% of full load current

A

115 - 125%

30
Q

What is a magnetic motor starter?

A

Electromagnet is used to operate a set of contacts for making and breaking the electric circuit.

31
Q

What does across the line mean?

A

The motor is started with full line voltage.

32
Q

What is a fuse called that provide both short circuit protection and overload protection?

A

Dual element time delay fuse

33
Q

Two types of starters

A

Clapper type, vertical lift type

34
Q

If the motor starter has tripped because of an overload, what must you do?

A
  1. Find out cause of overload
  2. Wait for OLR to cool down
  3. Reset OLR
35
Q

Low voltage starters are rated by the EEMAC, what is their lowest and highest rating?

A

Size 00 (2hp max), size 8 (900hp max)

36
Q

What elements does a power circuit usually contain?

A

Disconnect switch, NO contacts (go rated contacts) overload heaters, fuses (overcurrent protection)

37
Q

Isolation switches are horsepower rated, T/F?

A

False. They are not.

38
Q

What is the fundamental difference between a two wire and three wire control circuit?

A

The additional NO contact in parallel with the start button in the three wire switch.

39
Q

When are TX’s used in a control circuit?

A

CT’s are used to step down the line voltage from the power circuit to operate at a safer level

40
Q

What do wiring diagrams show?

A

Shows the physical relation of all devices and each conductor termination between each device.

41
Q

What do ladder diagrams show?

A

Symbols and lines identifying components in the electrically connected way

42
Q

What is the dangerous version of a jogging circuit called?

A

Double block, or blocking

43
Q

Name two versions of jogging circuits that work and are safe.

A

Control relay, jog run selector switch

44
Q

Are shading coils needed for DC coils?

A

No

45
Q

What is the purpose of a motor starter?

A

Stop, start a circuit, and provide OLP

46
Q

Four enclosure types for motor starters.

A

Open (not enclosed), explosion proof, waterproof, dust proof

47
Q

What is a downside to using bimetallic strips for overload relays?

A

High ambient temperatures can cause nuisance trips

48
Q

Disadvantage if manual motor starters compared to magnetic motor starter?

A

Manual motor starters do not provide low voltage protection

49
Q

Why must starters be connected to the ungrounded conductor?

A

Ground condition could bypass the motor running protection

50
Q

What are the two different types of contacts in a magnetic starter?

A

Stationary, moving

51
Q

Fuses act quicker than overload relays. T/F?

A

False. OLR act quicker.

52
Q

What type of contact is the overload relay in the control circuit?

A

Normally closed auxiliary contact

53
Q

Magnetic type overload relays are _______ type

A

Solenoid

54
Q

Thermal overload relays are _______ type

A

Heater

55
Q

Why are components rated in horsepower?

A

So that they can safely handle in rush current and full load current

56
Q

What is the purpose of a motor starter?

A

Stop, start, provide overload protection

57
Q

Define in-rush current

A

Locked rotor current. Current drawn by the motor when first energized.

58
Q

What are push button starters rated at?

A

5HP @ 230V

59
Q

Why is a motor rated in HP and not just current?

A

Must be able to interrupt locked rotor current

60
Q

Example of a two wire pilot device

A

Float switch, thermostat, flow switch

61
Q

What is electrical interlocking?

A

Connection of contacts in control circuit to prevent forward and reverse from being energized at the same time

62
Q

Why are both electrical and mechanical interlocks used?

A

Electrical interlocks act quicker than mechanical interlock, but electrical interlocks can fail. Arching can cause an uneven surface on the contacts which can prevent them from acting normal.

63
Q

What are two different types of time delay relays? What are their differences?

A

Hydraulic and Pneumatic. Hydraulic is oil filled, pneumatic is air filled and uses bellows

64
Q

Advantages of timer relays

A

Automatic repeat of functions, multiple trip points available, long timing functions

65
Q

The overall pressure over which a pressure switch can function is called the ______

A

Differential

66
Q

Starter size required for a motor load depends on _____

A

Motor duty cycle

67
Q

There’s types of pressure switches

A

Bellows, diaphragm, bourdon tube

68
Q

What type of oil is used in a dashpot?

A

Silicon

69
Q

What are the two types of proximity switches?

A

Inductive: detects presence of metals

Capacitive: detects presence of almost any material

Level 2 Electrical, Canada (19 decks)

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