Notes Flashcards
What happens with current in AC motors?
large inrush currents when they start up and then current falls to rated values
As mechanical load increases the _________ will also increase?
current
Toggle switch and knife switch rating?
max rating is 1hp @230v
What does a toggle switch prevent and what is it sometimes called?
arcing
snap-action switch
Main difference between a regular switch and motor switch?
motor switch must be hp rated
T/F? Hp rating of a starter must meet or exceed the hp of the motor?
True
how is the starter connected with the supply line and motor terminals?
in series
Push button starter rating?
max 5hp @230v
Difference between push button starter and toggle switches?
push button starter uses two separate buttons to activate contacts
Drum-switch rating?
max 3hp @240v or 1.5hp @120v
What is a drum switch?
rotary action selector switch
what is a drum-switch used for?
used to control speed (no overload protection)
Does an isolating switch need to be hp rated?
No
What does an isolating switch do?
isolates machine without interrupting power source
Two most common overload relays?
melting-alloy
bi-metallic strips
What is thermal overload protection?
guards against mechanical overloading or high voltages
What is a melting-alloy overload relay often referred to as?
solder pot
what does a bi-metallic strip have?
a bi-metallic strip close to the heater element
What must you do when an overload occurs?
wait until it cools down before you reset it
Overload with toggle switch?
will move to center and must be switched off before turning back on
Overloading with push button types?
Button will extend fully and must be pushed in before pushing on
what does low voltage release mean?
motor will automatically restart when power returns
Overload definition?
a current greater than normal inside path (protected by OL relay)
Overcurrent definition?
A greater current than normal outside normal path (protected by the line fuses)
how many lines does single, double pole and three pole interrupt?
1
2
3
How are Stop Push buttons connected?
Series
How are Start Push buttons connected?
Parallel
What is located in the magnetic starter?
Seal in contacts, coil, and auxiliary overloads
Difference between two-wire and three-wire circuit?
Two-wire (low voltage release)
Three-wire (low voltage protection)
What are control relays used for?
used as auxiliary contacts to control low current coils of the magnetic starter
Hand off auto selector switch?
used for manual and automatic controls
What are control relays used for?
Lights, alarms, small motors, or electric heaters
What are control relays also known as?
poles
What are contacts usually rated at?
10amps , as high as 600v AC
Name the three different current ratings?
Inrush or make contact ratings
Normal or continuous rating
Opening or break contact rating
why are jogging circuits dangerous?
there is a chance of the contacts staying closed
