Miscellaneous Flashcards
Wire colour coding for 3 phase in Canada?
Red, Black, Blue/White
Outside the magnet, lines of force travel?
North to South
Inside the magnet, lines of force travel?
South to North
Another name for magnetic lines of force?
magnetic flux
Magnetic lines of force never cross. True or False?
True
Magnetic lines of force start at the North Pole and end at the South Pole. True or False?
False
What is Impedance?
Opposition to AC current flow
what determines voltage rating of a conductor?
Insulation of the conductor
As the current in a conductor is increased, what happens to the magnetic lines of force surrounding the conductor?
More lines of flux are formed and forced outward.
As the current in a conductor is decreased, what happens to the magnetic lines of force surrounding the conductor?
Lines of force collapse inwards
Any material that will readily release electrons is called
conductor
Best semi-conductor?
Silicon
A conductor has ____ or less valence electrons while an insulator has ___ or more
3 or less
5 or more
Semi-conductor has how many electrons in its valence shell?
4
Using the left-hand rule for coils, the thumb points in the direction of
flux lines or North Pole of coil
List four things that affect the strength of an electromagnetic coil.
Spacing between coil
Number of turns in coil
Magnitude or current flow
Type of core material
Materials that act in a similar way to iron in a magnetic field are referred to as _____________ materials
ferromagnetic
What is the most practical way of varying the strength of an electromagnet?
- What device connected in series is used to do this?
vary current though the coil
- Rheostat
The magnetic flux in a circuit is directly proportional to the ________________and inversely proportional to the of_______________ the magnetic circuit.
Magnemotive force
Reluctance
Opposition to the formation of flux lines in a magnetic circuit is called
Reluctance
The spreading out of the flux lines in an air gap is referred to as
Fringing
As the reluctance of a magnetic circuit is increased, the flux density of the circuit is
decreased
If the magnetomotive force applied to a magnetic circuit is increased, the flux density of the circuit is
increased
Magnetic cores are usually constructed from materials with a high _____________ and a low ______________
permeability
reluctance
The amount of energy lost due to the constant reversals of the magnetic field in AC circuits is referred to as
Hysteresis
A _________ is a wire wound into a helical coil for the express purpose of creating a stronger magnetic field.
solenoid
What is a type of electromagnetic switch?
Relay
The electric meter on a house measures the _______ passing through it.
wattage
An electric motor is an inductive load. True or False?
True
What is NOT a factor in determining impedance in an AC circuit?
frequency
Overload protection is?
125%
Relay protection is?
140%
Overcurrent protection is?
225%
A _______ -_____ is commonly used on a single phase fractional horse power compressor motor to disconnect the start winding after the motor starts
current-relay
Direction of rotation of a single phase induction motor is determined by;
direction of current flow through the start winding
The capacitor start-capacitor run (CSCR) motor provides;
high starting and running torque
Capacitors are always connected in __________ to the start winding
series
On a 3-phase motor, all three legs resistance should be?
Equal
On a single-phase motor, Resistances should be additive. True or False?
True
On a single phase compressor, terminals “CSR” shall have values of?
S-R = Most
C-S = Middle
C-R = Least
When checking the windings of a three phase motor;
All three windings shall read the same resistance
When testing the windings of a single phase motor, which terminals show the lowest resistance?
Common to run
O/L and infinity readings are the same. True or False?
True
If one winding shows significantly lower resistance compared to the others, it may indicate a short circuit. True or False?
True
Relays are generally used to control inductive loads up to ______ amps.
25
Contactors are rated according to the maximum amperage through the;
contacts
when testing a motor with an ohmmeter, the run winding shows 1,000 ohms to the motor frame. This indicates;
It is grounded
When the temperature of a negative temperature coefficient (NTC) thermistor increases, its resistance will;
decrease
When the temperature of a positive temperature coefficient (PTC) thermistor increases, its resistance will;
increase
Capacitance measures a capacitor’s ability to ____.
storage a charge
When a capacitor is used in an ac circuit, the current _____ voltage by ____ degrees in a pure capacitive circuit.
leads
90
Current lags voltage by 90° in a pure inductive circuit. True or False
True
A start capacitor will heat up during normal use. T or F?
False
Capacitors can be charged with either dc or ac. True or False?
True
As capacitance increases, resistance increases. T or F?
False
Capacitors are charged and discharged every half cycle. T or F?
True
An open capacitor will be displayed as a value in the picofarad range in most multimeters in capacitor mode.
True
A faulty capacitor can be replaced with a capacitor that has a lower voltage rating. T or F?
FALSE
Voltage rating for replacement capacitor must be equal to or higher than OEM. True or False?
True
Capacitors with different capacity values that share one common plate
Dual capacitor
Wiring capacitors in Parallel _______ capacitance
double
Wiring capacitors in Series ________ capacitance
cut in half
Capacitors connected in series _______ voltage
increase
Capacitors connected in parallel the voltage is?
same?
Assists a motor in starting up
Start capacitor
Energized while the motor is operating
Run capacitor
Insulator between the plates in a capacitor is called a
Dielectric
Type of capacitor found in circuit boards for primarily dc use are _________
polarized
Type of capacitor used for single-phase motors _____-_________
non-polarized?
Are capacitors used in three-phase motors?
NO
Large-value capacitor
Electrolytic
Capacitors oppose the change in voltage potentials as they charge and discharge, and the opposition that results in resistance to current flow is called capacitive ________
Reactance
If off on internal overload and hot, you will read what between C-R and C-S?
Open/Infiniti
Think of an AC waveform
- Resistive circuit - voltage and current are ___ phase
- Capacitive circuit current _____ voltage by ___degrees
- Inductive circuit current ____ voltage by __deg
IN
leads, 90 deg
lags, 90 deg
3-phase phase angle is = to ______ degrees
120 degrees
Single phase peak is ___ degrees and negative peak is ____ degrees and ____ degrees at 0
90 degrees
270 degrees
180 degrees
Run capacitor must be _________ or greater than voltage applied
GREATER
start capacitor must be ________ to or greater than voltage applied
equal to or greater
voltage applied to start cap never exceeds ___%
130%
voltage applied to run capacitor never exceeds ____%
110%
