Motor Starters 030204e Flashcards
What are magnetic motor starters typically enclosed in?
Metallic or non-metallic enclosure.
What are some devices that are mounted on a magnetic motor starter?
Stop or start buttons.
Overload Reset Buttons.
Indicator Lights.
Alarm Buzzers.
What are some components located within the motor starter enclosure?
Control Transformers.
Terminal Strips.
Overcurrent Devices.
What components make up a magnetic contactor?
Stationary Contact.
Moveable Contact.
Pressure springs.
Operating coil.
Stationary electromagnet.
Magnetic shading coil.
Moving armature.
What may have to be added to a contactor as auxiliary contacts?
Holding Contacts.
What is the advantage of using an electrically operated switch over a manual switch?
Can be remotely controlled.
What type of operating coil is normally used for a contactor for a magnetic motor starter?
Solenoid type. Since the coil is separate from the core, it is typically replaceable.
What voltage must the operating coil be rated for?
Must be rated for the voltage of the control circuit from which it will be operated from.
What is a control transformer needed for?
May be needed to reduce the supply voltage to the correct voltage for the control circuit.
What is a common reason for starter failure?
Incorrect coil voltage is applied.
How must power circuit contacts be connected and what must they be able to do?
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.
What circuits are auxiliary contacts used for?
Pilot duty. Used for switching control circuits only. Not meant to carry full load motor currents.
Why is the voltage rating listed on the nameplate of a motor lower than the normal voltage of a system it is connected to?
Voltage drop.
Voltage drop in the motor feeders and branch circuit conductors is expected.
What are the two voltage ratings of the contactor in a motor starter?
Power contact voltage ratings.
Coil voltage rating.
What is the advantage of using a Class 2 control transformer to supply the control circuit of a motor starter?
Less restrictive wiring methods.
What are the two basic styles of magnetic motor starters?
NEMA (National Electrical Manufacturers Association)
IEC (International Electrotechnical Commission)
What are the advantages and disadvantages of NEMA motor starters?
Advantage: Come preassembled and partially pre-wired.
Disadvantage: Less compact (larger) and have live exposed parts. Require guarding by an enclosure or other means.
What are the advantages and disadvantages of IEC motor starters?
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.
What is referred to as jogging duty?
When a motor is started and stopped frequently.
What are the four motor characteristics for selecting a NEMA motor starter?
Full load current (FLC) of the motor.
Voltage rating of the motor.
Horsepower rating of the motor.
Motor duty (Continuous or jogging).
What are the considerations for selecting an IEC contactor?
Current, voltage and horsepower rating of the motor. IEC contactors are classified based on specific use categories.
What are some of the use categories for IEC contactors?
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.
What factors are needed to be considered when selecting an overload device for a motor starter?
Full Load Current (FLC) of the motor.
Service Factor of the motor.
What are the three types of magnetic motor starters?
Full voltage (across-the-line).
Reduced voltage.
Reversing.
What is a full voltage or across-the-line motor starter?
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.
What is a reduced voltage starter?
Limits the effects of inrush current during motor start-up by applying a lower voltage at start-up.
What is a reversing motor starter?
Reverses shaft rotation of a three-phase motor by interchanging any two line conductors that supply the motor.
Which type of motor starter has 2 contactors as part of the assembly?
Reversing motor starters.
One contactor operates the motor in one direction and the other contactor operates the motor in the opposite direction.
What are some factors to consider when selecting a motor starter enclosure?
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.
What are some common types of motor starter enclosures and their uses?
Type 1 - General-use indoors.
Type 3R - Outdoors.
Type 4 - Watertight.
Type 12 - Dust-tight indoors.
Type EX - Hazardous locations.
What is a combination motor starter?
Includes a disconnecting means, overcurrent device and motor starter into one enclosure.
Might also include a control circuit transformer, push buttons, and indicator lights.
What are the two temperature nameplate ratings for motors?
Ambient temperature rating.
Temperature rise rating.
What does the ambient temperature rating mean on for motors?
Indicates the temperature of the medium used to cool the motor, which can be oil, gas, or air.
What does the temperature rise rating mean on motors?
How much hotter the inside of the motor will get above the ambient temperature when the motor is operating at full load conditions.
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?
How often the motor is required to start (duty).
The time taken for the motor to get up to speed.
Mechanically overloading the motor.
What are the two sections of an overload relay for?
One section senses the current in the motor’s power circuit.
One section responds to that current.
What are the two ways the overload relay can sense the current flowing to the motor?
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.
What are the two main types of overload relays?
Thermal & Magnetic.
Speed at which an overload relay reacts to an overload condition is determined by what?
It’s Trip Class.
What are the three main trip classes for motor starters?
Class 10
Class 20
Class 30
What current percentage of the overload rating will cause a motor trip class to actually trip?
600%
What are heaters element (heaters) components in thermal overload relays for?
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.
What can happen if the incorrect current rating or setting for heaters (heater elements) is used?
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.
What are two types of thermal overload relays?
Melting alloy.
Bimetallic strip.
What motor starter manufacturer is melting alloy thermal overloads used in?
NEMA
What are melting alloy relays also referred to as?
Eutectic alloy or solder pot.
What is an advantage of melting alloy overload relays?
They are not prone to nuisance tripping caused by vibration.
When should melting alloy overload relays not be used?
When there is a large variation in ambient temperatures.
What are some advantages of magnetic overloads over thermal overloads?
Do not rely on heat dissipated by a heater element making them more efficient.
They are also unaffected by ambient temperature.
What are some common methods to delay tripping with magnetic overloads?
Adjustable electronic time delay.
Adjustable armature.
Fluid-filled dashpot.
What are the two types of magnetic overload relays?
Electromagnetic.
Solid-state.
Which type of overload relay does not have any moving parts?
Magnetic solid-state overloads.
What is an enhanced version of a solid-state overload referred to as?
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).
Why can melting alloy overloads not be automatically reset?
To give time for the alloy to cool and solidify.
How do electromagnetic overload relays sense the magnetic flux of the motor current?
A current transformer.
What type of motors are manual motor circuit switches used for?
Smaller single-phase motors of 1/3 hp or less.
What are some applications for manual motor circuit switches?
Fans.
Small water well pumps.
Sump pumps.
What is another name for manual motor circuit switches and why?
Manual motor starters.
Have built in overload protection and act as both a controller and disconnecting means.
What are all the standard ratings for fuses?
30A, 60A, 100A, 200A, 400A, 600A, 800A, 1200A
What factors do you need to know when using Table 29 to determine the rating of the motor branch circuit overcurrent device?
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.
What is the service factor on a motor nameplate?
Ability to withstand periods of overload without damage.
What is the service factor of a motor if it is not listed on the nameplate?
Service factor of 1.
What is the maximum setting for overload devices if the motor has a service factor of 1.15 or greater?
125%
What is the maximum setting for overload devices if the motor has a service factor of 1.15 or less?
115%
Non-horsepower rated switches can be used as a disconnecting means if they can safely do what?
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.
If an armature is pushed in manually for troubleshooting, what terminals should have no resistance?
L1 and T1
L2 and T2
L3 and T3
2 and 3 (NEMA holding contacts)
13 and 14 (IEC holding contacts)
If an ohmmeter reads over the limit (OL) when an armature is pushed in, what could this indicate?
Jammed armature.
Damaged contacts.
Burnt-out heater in the overload relay(for the power contacts.)
What should you see on an ohmmeter when an armature is opened versus when it is closed?
Closed - should read zero ohms to indicate continuity.
Open - should read OL to show they have properly opened and no issues.
What could it indicate if you get an OL reading on an ohmmeter when testing the operating coil?
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.
