HVAC electrical study guide
which of the following is equal to 100 milliamps
0.10 amperes
three 300 ohm resistors are wired in parallel. the total resistance equals
100 ohms
The synchronous speed of a four pole, 60 Hz single phase motor is
1800 rpm
how many watts of power are used by a heater operating at 460 volts and drawing 5 amps?
2300 watts
three defrost heaters, each 15 ohms are wired in parallel to a 120 volt power supply. how many watts of power will be used?
24 watts
utility companies usually supply residential domes with ________service
240 V, single phase, three wire
what is the minimum number of wires required between two start/stop push button controls?
3
Which of the following is an acceptable temporary replacement for a run capacitor rated at 35MFD @ 440VAC
37.5MFD @440VAC
a parellel circuit consist of three resistors R1=30 ohms R2=15 ohms R3 = 10 ohms if the current through R2=4 amperes, white is the sources voltage?
60 volts
resistance can be calculated by
E divided by I
which of the following motors is most energy efficient
ECM
the symbol for current is:
I
transformers are rated according to
VA at the secondary
any material that will readily release electrons is called:
a conductor
in a series circuit, the voltage drop across each resistance (load) will
add up to equal the source voltage
when checking the winding of a three phase motor
all three terminals should show the same resistance
to. change direction of rotation of a three phase motor
change the position of any two supply
When the temperature of a negative temperature coefficient (NTC) thermistor increased, its resistance will ...
decrease
the capacitor start -capacitor run (CSCR) motor provides
high starting and running torque
capacitor are always connected _______ to the start winding
in series
When the temperature of a positive temperature coefficient (PTC) thermistor increases, its resistance will ...
increase
capacitors are rated in
microfarads and voltss
technicians #1 says that an OPEN transformer coil is indicated by a reading of 0 ohms on an analog ohmmeter technician #2 says that a SHORTED transformer coil in indicated by reading of infinity on an analog ohmmeter who is correct?
neither technicians #1 nor #2
single phase motor speed is determined by the
number of stator poles
what type meter uses it own battery?
ohmmeter
if contacts become badly pitted, it is acceptable to
replace the contacts or control
what is the term used to describe the output side of a transformer
secondary side
excessive current can be caused by
short circuit
which of the following materials would be best suited for use as a semi-conductor?
silicone
current flow is:
the flow of electrons in the circuit
in electrical wiring, a black colored wire usually indicates
the hot conductor
when resistors are wired in parallel
the voltage drop across each resistor will be the same as the applied source voltage
a three phase load requires a minimum of
three supply lines
a 240 volts, 3 wire circuit can be split into two 120 volts ciruits
true
the safety ground conductor is usually color coded
white
circuit fuses and breakers are primarily used to protect
wiring
which of following is the correct formula for determining wattage in an electrical circuit
W=E times I
the terminal T1,T2,T3 are located at the ____of a contactor
bottom
which of the following statements about current is true
current flow will increase when voltage increase
a solenoid valve coil operates on the principle of
electromagnetism
the total resistance of a parallel circuit will be
less than the smallest resistance
a device with overload protection used to control a motor is a
line starter
when current flows, a _________ is produced around the conductor
magnetic field
the _______ drawing illustrates where the components are located in small appliances
pictorial
A transducer can create a signal based on..
pressure
an electronically commuted motor(ECM) is designed to
provide proper air flow under various conditions
in single phase motor, which winding has the most resistance
start
a capacitor analyzer is designed to read
the capacitance of a capacitor
To discharge a capacitor prior to ohmmeter testing
use a 20,000 ohm, 2 to 5 watt resistor across the terminals
which of the following is equal to 2.1 kw
2,100 watts
the voltage to ground of a "high leg" on a three phase open Delta system will be approximately
208
a transformer has 1000 turns of wire in the primary coil and 2000 turns in the secondary coil. if 120 colts are applied, the output voltage will be
240 volts
relays are generally used to control inductive loads up to ____amps
25
what is generally considered to be the maximum allowable (plus or minus) supply voltage variation
5%
a parallel circuit contains a 18 ohm and a 9 ohm resistor. the total resistance equals:
6 ohms
how much resistance must be placed in a 120 volt circuit in order to limit the current to 2 amps?
60 ohms
a transformer has 1000 turns of wire in the primary coil and 500 turns in the secondary coil. if the 120 volts are applied, the output voltage will be
60 volts
one horsepower is equal to ________ watts
746 watts
voltage can be calculated by
I times R
resistance is:
The opposition of current flow.
when testing a motor with an ohmmeter, the run winding shows 1000 ohms to the motor frame. this indicates?
a grounded condition
an ohmmeter should never be connected to
a live circuit
an electron has
a negative charge
contractors are rated according to the maximum amperage through the
contacts
a diode is used to
control the direction of electron flow
a _______ is commonly used on a single phase fractional horse power compressor motor to disconnect the start winding after the motor starts
current relay
when testing a capacitor with an analog ohmmeter, the needle on the meter should
deflect towards zero then return to infinite reading
which of the following would be considered an inductive load
electric motor
which of the following is NOT a factor in determining impedance in an AC circuit?
frequency
A typical thermocouple used on a gas furnace can ..
generate a small DC electrical current
with the motor running at full load, voltmeter leads are placed on L1 and T1 terminals of the contractor. The voltmeter indicates no measurable voltage. This is an indication of:
good clean contacts
if the conductor in an AC circuit is wound into a coil, the resulting EMF opposes the supply voltage. the opposition is called
inductive reactance
the thermal overload contacts on a line starter are usually _______reset
manual
which meter is used to bench check a motor for shorts or open windings
ohmmeter
two 120 colt incandescent light bulbs are wired in series, one is a 60 watt bulb, the other is a 4 watt bulb. the results would be
only the 4 watt bulb will light
impedance is:
opposition to alternating current flow
like charges:
repel each other
when testing the winding of a single phase motor
the common to run terminals show the lowest resistance
direction of rotation of a single phase induction motor is determined by
the direction of current flow through the start winding
a step up transformer increases
voltage
fuses are sized by
volts and amps
the electric meter on a house measures the _____ passing through it
wattage
