328 Flashcards
Magnetic Motor Starters and Circuit Overview
What is a Full Voltage or Cross-the-Line Magnetic Motor Starter
This is a starter that uses voltage and current to start a motor or interrupt a motor (stopping it).
What Does a Magnetic Starter Rely on to Open and Close its Contacts
An electromagnet (coil).
What are the Parts of a Magnetic Starter
A contactor section (top half) and an overload section (bottom half). They are distinct and separated, but are connected together with wires or bars.
What Does a Magnetic Motor Starter Control
It controls power applied to the motor windings.
What Function Does a Full Voltage Motor Starter Perform
It can apply or cut out voltage going to a motor.
What is the Difference Between Motor Starter Contactor section and a Regular Contactor
The contact sets for a motor starter may have different current ratings, with a higher current rating for the sets connected to power (labeled L1, L2, or L3) . While on a regular contactor the contact sets have the same current rating.
What’s the Reason a Motor Starter Contactor Set for Power has a Higher Current Rating
This is due to its physical size, this allows it to be rated higher.
How Many Circuits are Typically Used in Motor Control
2, Motor circuit and control circuit.
What is the Function of a Motor Circuit
This is used to feed current and power up a motor.
What is the Function of a Control Circuit
This is used to power contactor coils, indicators, and lights.
Describe the Connections Made to a Motor Starter for the L and T Sides
Power is connected to the L side of the starter and the motor is connected to the T side (load) of the starter.
What Position are Contacts a Motor Starter (Top Part) Typically Designed in
They are designed to be normally open (NO) and made to handle an inrush of motor starting current.
How High is a Motor Starting Current
It is about 6 times the full load amps (FLA)
what is Locked Rotor Current (LRC)
This occurs when a motor is running and its shaft is stopped while still energized. This is because the motor is loaded heavily and cannot run.
How High Can a Locked Rotor Current (LRC) Be Rated
At about 10-20 times the full load amps (FLA).
What is Contained in the Overload Section of a Starter
An overload relay that opens when conditions for an overload are met. It wont open during a ground fault or short circuit.
What Circuit is the Overload Relay Connected to
It is connected to the control circuit and mot the motor circuit.
Where is an Overload Relay Placed on a Ladder Diagram
Between the starter coil and L2.
Thermal Protectors in a Starter are in ___ with the Motor Circuit Conductors
Series.
Some Starters Come with_____ Indicators
Trip.
In what Position are the Contacts for an Overload Relay Designed
Normally Closed (NC).
Why do Some OL Relays Come with Both a NC and NO contact
This is because the NC contacts (open when tripped) serves to remove power from the coil, and the NO contact (closes when tripped) is used as an indicator to inform whoever close by that there was an overload.
An OL Relay with Both a NC and NO Contact has a ____ Contact
SPDT. This can either be a single break or double break type.
What Does a Manual Starter Have Built-in with
A controller with a start-stop push button switch that is maintained and mechanically interlocked.
If a Manual Starter is Used as Both the Controller and Disconnecting Means of a Motor, It Must be ___
Within Sight of the Motor to be controlled.
A Controller for a Magnetic Starter can be Located
It can be located remotely away from the motor and you can have any number of controllers.
How is the Control Circuit for a Magnetic Starter Classified
As either a two-wire or three-wire control circuit.
What is a Two-Wire Control Circuit
This is a wiring system that allows automatic restarting of a motor when power has been disconnected and reconnected.
What Needs to be Done to have a Control Circuit Operate at the Same Voltage Rating as the Motor Circuit
The control circuit is tapped to the motor circuit at the line side of the starter.
Why is it Called a Two-Wire Control Circuit
This is because you have 2 wires installed from your remote controller to your starter.
Why Does a Two-Wire Control Circuit Pose as a Safety Hazard
For example, if there is a power outage and and it gets restored with no one aware that the motor is on a two-wire control circuit, they will be caught off-guard by the motor starting back up.
What is a Three-Wire Control Circuit
This wire control system prevents a motor from restarting after it is disconnected from power.
How Does the Three-Wire Control Circuit Prevent Restarting
It comes with two momentary NO set of contacts in parallel to each other. Generally the second set of contacts is the holding/memory contact in the starter.
What Kind of Control Device is Generally Used on a Three-Wire Control Circuit
A remote start-stop push button station.
Who Decides on Whether to use a Two or Three Wire Circuit
The circuit designer does based on the system requirements for operation.
What are Holding Contacts also Called
Memory or sealing contacts. For some starters they come built in, but for others they must be ordered separately to be installed.
What Position Must Holding contacts be in
In a normally open position, and operate with power contacts when the coil is energized.
What is the Relationship Between a Holding Contact and a Power Contact
They are Mechanically Interlocked, operating simutaneously.
What is an Auxiliary Contact
This is a smaller set of contact within a contactor it self. It acts based on the state of the main contactor it self.
What Kind of Contactor can also be Used as a Holding Contactor
A Normally Open Auxiliary Contactor.
What Forces a Contact to Change State when Energized
A plunger does (a Plastic or metal object).
What is a Holding Contactor
This is a normally open contactor that remains in it changed state when power is applied to it. This is with the help of the plunger.
What do you Call the Additional Contact Blocks on a Stater
These are called auxiliary contacts and can be NO, NC, or NO/NC. They can be used to control other starter coils.
Where can Auxiliary Contacts be Attached on a Starter
On the side or the top.
How do Auxiliary Contactors Operate in Relation with the Starter’s Contactor
They operate at the direction of the starter’s contactor. It changes state when the starter contactor changes state.
What Happens When a Contactor Point Disengages
There will be current tracking and arching on the surface of the contact points which damages the surface area leading to reduced ampacity at the contact points. It can also cause contact points to stick to each other or weld.
What Happens to Contact Points with Pitting and Scarring
This cause the contact points to have a higher resistance to current. Filling these point wont help, but may even damage special parts on the contact.
What is an Inductive Load
Any device with a coil or winding that creates a magnetic field when current is applied to it.
What is a Resistive load
Any device that turns current to heat when it is applied.
What is a Difference Between Inductive Loads and Resistive Loads in Reference to the Wear and Tear of Contacts
Inductive loads deal more wear and tear to its contacts than resistive loads.
Will a Motor Branch Circuit OCPD Open During an Overload
No it wont. You need to provide an additional means for overload protection on a circuit.
What Happens When a Motor Overloads
Excess heat is created and it damages the insulation of the winding conductors.
What are Built into Manual/Magnetic Starters
Contactors, overload protection, and thermal protection parts as well.
How Does Motor Control Current Flow in a Starter
It flows through the overload relay contacts.
What is Service Factor (SF)
This is the amount of overload current the motor can withstand or a given period without taking any damage, it is a % of your FLA.
When Does an Overload Device Engage
When there is an excess amount of current flow.
How Should Thermal Overloads be Replaced
Its should be replaced all at once.
Rather than Thermal Overloads, What do Newer Magnetic Starters Come With
Electronic Overloads.
Does OSHA Have Minimum Lighting Levels and How do they Range
Yes. Ranging from 3 ft - 30 ft candle. Ft candle is a unit of illuminance.
What are the OSHA Minimum Lighting Levels
3ft candles for concrete placement, storage/maintenance areas, etc.
5ft candles for general construction, indoor, tunnel, etc.
10ft candles for general construction plants, electrical equipment rooms, and shops.
30ft for first aid stations, offices, and infirmaries.
How are Inherent Protection Devices that are Built into the Motor Reset
It is reset automatically. These are built into the motor only and not the starter.
What are Some Types of Overload Relays
Melting alloy, bimetallic, and Magnetic.
What does a Heater Coil do
It senses ambient temperature and the heat generated by excessive current from the branch circuit.
What is not Included in an Open Type Starter
An Enclosure.
Does OSHA Permit Free-Standing Temporary Light Stands Being used on a Construction Site
Yes.
What is Considered Inaccessible
8ft and above.
