Motor Starters 030204e

Question 1

What are magnetic motor starters typically enclosed in?

Answer 1

Metallic or non-metallic enclosure.

Question 2

What are some devices that are mounted on a magnetic motor starter?

Answer 2

Stop or start buttons.

Overload Reset Buttons.

Indicator Lights.

Alarm Buzzers.

Question 3

What are some components located within the motor starter enclosure?

Answer 3

Control Transformers.

Terminal Strips.

Overcurrent Devices.

Question 4

What components make up a magnetic contactor?

Answer 4

Stationary Contact.
Moveable Contact.
Pressure springs.
Operating coil.
Stationary electromagnet.
Magnetic shading coil.
Moving armature.

Question 5

What may have to be added to a contactor as auxiliary contacts?

Answer 5

Holding Contacts.

Question 6

What is the advantage of using an electrically operated switch over a manual switch?

Answer 6

Can be remotely controlled.

Question 7

What type of operating coil is normally used for a contactor for a magnetic motor starter?

Answer 7

Solenoid type. Since the coil is separate from the core, it is typically replaceable.

Question 8

What voltage must the operating coil be rated for?

Answer 8

Must be rated for the voltage of the control circuit from which it will be operated from.

Question 9

What is a control transformer needed for?

Answer 9

May be needed to reduce the supply voltage to the correct voltage for the control circuit.

Question 10

What is a common reason for starter failure?

Answer 10

Incorrect coil voltage is applied.

Question 11

How must power circuit contacts be connected and what must they be able to do?

Answer 11

Must be connected in series with the supply conductors to the motor.
Must be able to interrupt the full load current (FLC) of the motor.

Question 12

What circuits are auxiliary contacts used for?

Answer 12

Pilot duty. Used for switching control circuits only. Not meant to carry full load motor currents.

Question 13

Why is the voltage rating listed on the nameplate of a motor lower than the normal voltage of a system it is connected to?

Answer 13

Voltage drop.
Voltage drop in the motor feeders and branch circuit conductors is expected.

Question 14

What are the two voltage ratings of the contactor in a motor starter?

Answer 14

Power contact voltage ratings.
Coil voltage rating.

Question 15

What is the advantage of using a Class 2 control transformer to supply the control circuit of a motor starter?

Answer 15

Less restrictive wiring methods.

Question 16

What are the two basic styles of magnetic motor starters?

Answer 16

NEMA (National Electrical Manufacturers Association)
IEC (International Electrotechnical Commission)

Question 17

What are the advantages and disadvantages of NEMA motor starters?

Answer 17

Advantage: Come preassembled and partially pre-wired.

Disadvantage: Less compact (larger) and have live exposed parts. Require guarding by an enclosure or other means.

Question 18

What are the advantages and disadvantages of IEC motor starters?

Answer 18

Advantages: More compact (smaller) and connections are typically enclosed. Less restrictive installation requirements.

Disadvantages: Contactors and overload relays are sold separately and combined in the field. Must ensure they are compatible with each other and the motor they are meant to control.

Question 19

What is referred to as jogging duty?

Answer 19

When a motor is started and stopped frequently.

Question 20

What are the four motor characteristics for selecting a NEMA motor starter?

Answer 20

Full load current (FLC) of the motor.

Voltage rating of the motor.

Horsepower rating of the motor.

Motor duty (Continuous or jogging).

Question 21

What are the considerations for selecting an IEC contactor?

Answer 21

Current, voltage and horsepower rating of the motor. IEC contactors are classified based on specific use categories.

Question 22

What are some of the use categories for IEC contactors?

Answer 22

AC-1 - Controlling non-inductive loads such as heating and general distribution loads.

AC-2 - Controlling slip ring (wound-rotor) motors.

AC-3 - Starting and stopping squirrel cage motors that are stopped under normal running currents.

AC-4 - Plugging, jogging, or inching squirrel cage motors.

Question 23

What factors are needed to be considered when selecting an overload device for a motor starter?

Answer 23

Full Load Current (FLC) of the motor.

Service Factor of the motor.

Question 24

What are the three types of magnetic motor starters?

Answer 24

Full voltage (across-the-line).

Reduced voltage.

Reversing.

Question 25

What is a full voltage or across-the-line motor starter?

Answer 25

Applies full rated voltage to the motor during starting. Is designed to handle the levels of inrush current that develop as the motor is started.

Question 26

What is a reduced voltage starter?

Answer 26

Limits the effects of inrush current during motor start-up by applying a lower voltage at start-up.

Question 27

What is a reversing motor starter?

Answer 27

Reverses shaft rotation of a three-phase motor by interchanging any two line conductors that supply the motor.

Question 28

Which type of motor starter has 2 contactors as part of the assembly?

Answer 28

Reversing motor starters. One contactor operates the motor in one direction and the other contactor operates the motor in the opposite direction.

Question 29

What are some factors to consider when selecting a motor starter enclosure?

Answer 29

Location of the motor starter (indoors or outdoors). If the starter will be exposed to moisture or corrosive substances. Starter is in a hazardous location.

Question 30

What are some common types of motor starter enclosures and their uses?

Answer 30

Type 1 - General-use indoors. Type 3R - Outdoors. Type 4 - Watertight. Type 12 - Dust-tight indoors. Type EX - Hazardous locations.

Question 31

What is a combination motor starter?

Answer 31

Includes a disconnecting means, overcurrent device and motor starter into one enclosure. Might also include a control circuit transformer, push buttons, and indicator lights.

Question 32

What are the two temperature nameplate ratings for motors?

Answer 32

Ambient temperature rating. Temperature rise rating.

Question 33

What does the ambient temperature rating mean on for motors?

Answer 33

Indicates the temperature of the medium used to cool the motor, which can be oil, gas, or air.

Question 34

What does the temperature rise rating mean on motors?

Answer 34

How much hotter the inside of the motor will get above the ambient temperature when the motor is operating at full load conditions.

Question 35

When a motor draws more than the rated full load current , the temperature rise of the motor is exceeded. What are some factors that can cause excess current?

Answer 35

How often the motor is required to start (duty). The time taken for the motor to get up to speed. Mechanically overloading the motor.

Question 36

What are the two sections of an overload relay for?

Answer 36

One section senses the current in the motor’s power circuit. One section responds to that current.

Question 37

What are the two ways the overload relay can sense the current flowing to the motor?

Answer 37

Detecting the amount of heat produced by a heating element connected in series with the motor. Detecting the magnetic flux produced by the motor conductor.

Question 38

What are the two main types of overload relays?

Answer 38

Thermal & Magnetic.

Question 39

Speed at which an overload relay reacts to an overload condition is determined by what?

Answer 39

It’s Trip Class.

Question 40

What are the three main trip classes for motor starters?

Answer 40

Class 10 Class 20 Class 30

Question 41

What current percentage of the overload rating will cause a motor trip class to actually trip?

Answer 41

600%

Question 42

What are heaters element (heaters) components in thermal overload relays for?

Answer 42

Give off heat proportional to the amount of current that flows through them. When a specified amount of heat is given off the contacts open and motor will de-energize. Connected in series in the power circuit.

Question 43

What can happen if the incorrect current rating or setting for heaters (heater elements) is used?

Answer 43

Current setting is too high - not give off enough heat to trip the contacts. Motor windings may be damaged. Current setting is too low - May give off too much heat causing nuisance tripping and heater burn out.

Question 44

What are two types of thermal overload relays?

Answer 44

Melting alloy. Bimetallic strip.

Question 45

What motor starter manufacturer is melting alloy thermal overloads used in?

Answer 45

NEMA

Question 46

What are melting alloy relays also referred to as?

Answer 46

Eutectic alloy or solder pot.

Question 47

What is an advantage of melting alloy overload relays?

Answer 47

They are not prone to nuisance tripping caused by vibration.

Question 48

When should melting alloy overload relays not be used?

Answer 48

When there is a large variation in ambient temperatures.

Question 49

What are some advantages of magnetic overloads over thermal overloads?

Answer 49

Do not rely on heat dissipated by a heater element making them more efficient. They are also unaffected by ambient temperature.

Question 50

What are some common methods to delay tripping with magnetic overloads?

Answer 50

Adjustable electronic time delay. Adjustable armature. Fluid-filled dashpot.

Question 51

What are the two types of magnetic overload relays?

Answer 51

Electromagnetic. Solid-state.

Question 52

Which type of overload relay does not have any moving parts?

Answer 52

Magnetic solid-state overloads.

Question 53

What is an enhanced version of a solid-state overload referred to as?

Answer 53

Microprocessor-controlled electronic overload relays. Are programmable devices that can monitor additional conditions on the motor other than just overload conditions. Some units are also designed to communicate with programmable logic controllers (PLCs).

Question 54

Why can melting alloy overloads not be automatically reset?

Answer 54

To give time for the alloy to cool and solidify.

Question 55

How do electromagnetic overload relays sense the magnetic flux of the motor current?

Answer 55

A current transformer.

Question 56

What type of motors are manual motor circuit switches used for?

Answer 56

Smaller single-phase motors of 1/3 hp or less.

Question 57

What are some applications for manual motor circuit switches?

Answer 57

Fans. Small water well pumps. Sump pumps.

Question 58

What is another name for manual motor circuit switches and why?

Answer 58

Manual motor starters. Have built in overload protection and act as both a controller and disconnecting means.

Question 59

What are all the standard ratings for fuses?

Answer 59

30A, 60A, 100A, 200A, 400A, 600A, 800A, 1200A

Question 60

What factors do you need to know when using Table 29 to determine the rating of the motor branch circuit overcurrent device?

Answer 60

Full load current rating of the motor (FLC). The type of overcurrent device (time-delay fuse, non-time-delay fuse, or circuit breaker). The type of motor.

Question 61

What is the service factor on a motor nameplate?

Answer 61

Ability to withstand periods of overload without damage.

Question 62

What is the service factor of a motor if it is not listed on the nameplate?

Answer 62

Service factor of 1.

Question 63

What is the maximum setting for overload devices if the motor has a service factor of 1.15 or greater?

Answer 63

125%

Question 64

What is the maximum setting for overload devices if the motor has a service factor of 1.15 or less?

Answer 64

115%

Question 65

Non-horsepower rated switches can be used as a disconnecting means if they can safely do what?

Answer 65

Make or break the locked-rotor current of the motor. 6 times the full load current (FLC) Example. Name plate says 50A. Must handle 300A.

Question 66

If an armature is pushed in manually for troubleshooting, what terminals should have no resistance?

Answer 66

L1 and T1 L2 and T2 L3 and T3 2 and 3 (NEMA holding contacts) 13 and 14 (IEC holding contacts)

Question 67

If an ohmmeter reads over the limit (OL) when an armature is pushed in, what could this indicate?

Answer 67

Jammed armature. Damaged contacts. Burnt-out heater in the overload relay(for the power contacts.)

Question 68

What should you see on an ohmmeter when an armature is opened versus when it is closed?

Answer 68

Closed - should read zero ohms to indicate continuity. Open - should read OL to show they have properly opened and no issues.

Question 69

What could it indicate if you get an OL reading on an ohmmeter when testing the operating coil?

Answer 69

Coil is burned out and needs to be replaced. Overload contact is open and needs to be reset. One of the pre-wired connections is open-circuited.