HVAC Electrical application practice Flashcards
Resistance can be calculated by
E divided by I
Any material that will readily release electron is called
A conductor
single phase motor speed is determined by the
Number of stator pole
A device used to control a motor is a
Relay
contactor
Line starter
All of the Above
The meter on a house measures the __ passing through it.
Wattage
Which of the following is the correct formula for determining wattage in an electrical circuit?
W= E time I
impedance in a circuit is the result of;
pure resistance
inductive reactance
capacitive reactance
all of the above
To change the direction of rotation of a three-phase motor;
change the position of any two supply wires
A transducer can create a signal based on a form of energy such as.
pleasure
heat
fluid flow
all of the above
what is current flow?
the flow of electrons in the circuit
when the temperature of a positive coefficient (PTC) thermistor increases, its resistance will
Increase
A solenoid valve operates on the principle of.
Electromagnetism
the synchronous speed of a four pole, 60 Hz single phase motor is
1800 rpm
which of the following statements about current is true?
current flow will increase when voltage increase
a transformer has 1000 turns of wire in the primary coil and 2000 turns in the secondary coil. if 120 volts are applied, the output voltage will be
240 volts
fuses are used to protect
wires
when checking the winding of a three-phase motor
all three terminals should show the same resistance
with a motor running a full load, voltmeter leads are placed on each side of the relay contacts. The voltmeter gives no measurable voltage. this is an indication of.
Good clean contact
in a single-phase compressor motor, which winding terminals have the most resistance?
run to start
Once horsepower is equal to __ watts?
746
What is the term used to describe the output side of a transformer?
Secondary side
Step-up transformer increase;
voltage
A capacitor opposes current flow in a circuit. This opposition is called;
Capacitive reactance
when the temperature of a negative temperature coefficient (NTC) thermistor increases. Its resistance will.
Decrease
Two 120-volt motors are wired in series, once is a 60-watt motor, the other is a 4-watt motor. the result would be.
Neither motor would operate normally
Capacitors are always connected__ to the start winding.
In series
A capacitor analyzer is designed to,
-read power factor percentage
-diagnose an open or shorted capacitor
-read the microfarad rating of a capacitor
all of the above
when current flows, a _ is produced around the conductor
Magnetic field
what is impedance?
opposition to alternating current
three resistors are wired in series, each has a value of 300 ohms. what is the total resistance of the circuit?
900 ohms
how many resistances must be placed in a 110-volt circuit in order to limit the current to 2 amps?
55 ohms
what type of meter uses its own battery?
ohmmeter
A 240 volt, 3 wire circuit can be split into two 120 volt circuits
True
which of the following is equal to 2.1 kv?
2,100 volts
the safety ground conductor is usually color coded
Green
An electron has
A negative charge
what is resistance?
opposition to current flow
what is generally considered to be the Maximum allowable (plus or minus) supply voltage variation?
10%
the terminals T1, T2, T3 are located at the _ of a contactor
Bottom
in electrical wiring, a black colored wire usually indicates.
the hot conductor
electricity can produce
heat
light
Magnetism
all of the above
which of the following is equal to 100 milliamps?
0.10 amperes
A transformer has 1000 turn of wire in the primary coil and 500 turns in the secondary coil. if 120 volts are applied, the output voltage will be
60 (x/120x500/1000= 60,000/1000)
the capacitor start- capacitor run (CSCR) motor,
High starting torque
high running torque
like charges will
repel each other
what meter is used to bench check a motor for shorts or open Widings?
ohmmeter
Amperes can be calculated by
E divided by R
W divided by E
The square root of W divided by R
the symbol for current is
I
when resistors are wire in a parallel
the voltage drop across each resistor will be the same as the applied source voltage
contactors are rated according to the maximum amperage through the
contacts
an ohmmeter should never be connected to
a live circuit
the_ drawing illustrates where the components are located on the appliance.
pictorial
if the conductor in an AC circuit is wound into a coil, the resulting EMF opposes the supply voltage. this opposition is called,
inductive reactance
when testing a capacitor with an analog ohmmeter, the needle on the meter should,
Deflect towards zero then return to infinite reading
direction of rotation of a single-phase induction motor is determined by
the direction of current flow through the start winding
the thermal overload contacts on a line starter are usually _ reset.
manual
to discharge a capacitor prior to ohmmeter testing
use a 20,000-ohm resistor to short across the terminals
voltage can be calculated by
I time R
how are fuses sized?
Amps
volts
capacitors are rated in
Microfarad
Volts
transformers are rated according to
AV at the secondary
the total resistance of a parallel circuit will be
less than the smallest resistance
relays used in the HVAC industry are generally used to control loads up to _ amps
25
utility companies usually supply residential homes with a _ service
240v, single phase, three wire
a parallel circuit contains an 18 ohm and a 9-ohm resistor. the total resistance equals
6 ohms
in the schematic, the crankcase heater will operate
when the compressor is off
