Controls & Switching Circuits Flashcards
A reversing motor starter requires how many power contacts?
Six
What are the two types of interlocks in a motor control circuit?
Mechanical & Electrical
Excessive current causes a coil to burn out in a reversing starter motor. Which type of interlocking would you use to prevent this?
Electrical Interlocks
What would the terminal numbering be for the reverse holding circuit on an IEC reversing starter?
13 & 14
Name the SEVEN sections of the control circuit of a reversing starter.
General Stop
Forward Stop
Reverse Stop
Forward Start
Reverse Start
Forward Holding
Reverse Holding
What does pushbutton interlocking do?
It allows you to change the motor direction without having to first depress the stop button.
Where is the Overload placed on the schematic of a NEMA reversing starter?
On the right side
Why is mechanical interlocking required?
To prevent both contactors from pulling in at the same time and causing line to line short
What sort of equipment may require jogging or inching?
Cranes, Hoists, Printing processes and large lathes
If a motor is started at a reduced voltage to let the machine creep to the desired location, the function is known as:
Inching
When a motor can be jogged successfully, regardless of time required, it is called _________ __________
Positive Jogging
Three devices most often used to open or close a circuit are
Pushbutton contacts
Selector switches
Relay contacts
Positive jogging is a connection method that prevents the motor from accidentally going into run if the button is released very quickly. T or F?
True
The starting current of a three-phase induction motor can be how many times its full-load current?
Two to eight times larger
Which part of the circuit must be affected to achieve jogging?
Holding circuit
It is possible for the same button to be used for a start function and a jog function. T or F?
True
Pilot lights indicate the conditions of a motor circuit. Name some examples of what they may indicate:
Power on to a motor controller
Contactor energized
Overload trip of the overload relay
A standard pushbutton is an example of what sort of contact? And has what type of action?
Momentary. Snap Action.
Pilot lights are connected in series with operating coils. T or F?
False. Pilot lights are connected in parallel with operating coils or in SERIES with contacts.
How many basic IEC contactor use categories are there?
Four.
AC-1
AC-2
AC-3
AC-4
What information would you need to determine the maximum hp rating for a motor starter?
-Voltage
-number of phases
-Type of Duty
