HVAC Electric
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
1800rpm
how many watts of power are used by a heater operating at 460 volts and driving 5 amps?
2300 watts
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
Utility companies usually supply residential homes with________service
240v, single phase, three wire
Relays are generally used to control inductive loads up to ________ amps.
25
Three defrost heaters, each 15 ohms are wired in parallel to a 120 volt power supply. How many watts of power will be used?
2880 Watts
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
what is generally considered to be the maximum allowable supply voltage variation?
5%
A parallel circuit contains a 18 ohm and a 9 ohm resistor. the total resistance equals;
6 ohms
a parallel circuit consists of three resistors. R1=30 ohms R2=15ohms R3=10ohms if the current through r2=4 amperes, what is the source voltage?
60 volts
a transformer has 1000 turns of wire in the primary coil and 500 turns in the secondary coil. 120 volts are applied, the output voltage will be;
60 volts
One horsepower is equal to 746 watts
746
When checking the windings of a three phase motor?
All three terminals should show the same resistance.
a _____________is commonly used on a single phase fractional horse power compressor motor to disconnect the smart wilding after the motor starts.
Current relay
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
Voltage can be calculated by;
I times R
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 componets are located in small appliances
Pictorial
a capacitor analyzer is designed to read;
The capacitance of a capacitor
When testing the windings of a single phase motor?
The common to run terminals show the lowest resistance
current flow is:
The flow of electrons in the circuit
Any material that will rapidly release electrons is called;
a conductor
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
in a series circuit, the voltage drop across each resistance (load) will;
add up to equal the source voltage
to change direction of rotation of a three phase motor;
change the position of any two supply wires
which of the following is not a factor in determining impedence in an AC circuit?
d.frequency
when the temperature of a negative temperature coefficient(NTC) thermistor increases, its resistance will;
decrease
the capacitor start-capacitor run (CSCR) motor provides;
high starting and running torque.
when the temperature of a positive temperature coefficient(PTC) thermistor increases, its resistance will;
increase
If the conductor in an ac circuit is wound into coil, the resulting EMF opposes the supply voltage. This opposition is called;
inductive reactance
the total resistance is of a parallel circuit will be
less than the smallest resistance
Circuit fuses and breakers are primarily used to protect;
loads
Which meter is used to bench check a motor for shorts or open windings?
ohmmeter
what type of meter uses its own battery?
ohmmeter
impedance is:
opposition to alternating current flow
resistance is
opposition to current flow
A transducer can create a signal based on;
pressure
like charges;
repel each other
If contacts become badly pitted, it is acceptable to;
replace the contacts or control
what is the term used to describe the output of a transformer?
secondary side
excessive current can be caused by;
short circuit
which of the following materials would be suited for use as a semiconductor?
silicone
In a single phase motor, which of the winding has the most resistance?
start
direction of rotation of a single phase induction motor is determined by;
the direction of current flow through the start winding
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
the terminals T1, T2, & T3 are located at the _______ of a contactor
top
a 240 volt, 3 wire circuit can be split into two 120 volt circuits.
true
to discharge a capacitor prior to ohmmeter testing;
use a 20,000 ohm, 2 to 5 watt resistor across the terminals.
fuses are sized;
volts&s
which of the following is equal to 2.1KW
2,100 Watts
the voltage to ground of a "high leg" on a three phase open delta system will be approximately;
208
how much resistance must be placed in a 120 volt circuit in order to limit the current 2 amps?
60 ohms
a diode is used to;
Control the direction of electron flow
Capacitors are always connected ______________ to the start winding.
In series
Capacitators are rated in:
Microfarads & volts
Single phase motor speed is determined by the;
Number of stater poles.
an electronically commutated motor(ECM) is designed to
Provide proper air flow under various conditions.
transformers are rated according to;
VA at the secondary
two 120 volt incandescent light bulbs are wired in series, one is a 60 watt bulb the other is a 4 watt bulb. The result would be;
both bulbs light
Contactors are rated according to the maximum amperage through the?
contacts
which of the following statements about current is true?
current flow will increase when voltage increases
When testing a capacitor with an analog or digital ohmmeter, the meter should?
deflect towards zero than return to infinite reading
which of the following would be considered an inductive load?
electric motor
A solenoid calve coil operates on the principle of;
electromanetism
a typical thermocouple used on a gas furnace can;
generate a small DC electrical current.
With a motor running at full load, voltmeter leads are placed on L1. and T1 terminals of the contactor. The voltmeter indicates no measurable voltage. This is an indication of?
good clean contacts
the safety ground conductor is usually color coded;
green
The thermal overload contacts on a line starter are usually______reset
manual
Technician #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 is indicated by a reading of infinity on an analog ohmmeter.
technician #2 only
a step up transformer increases;
voltage
which of the following is the correct formula for determining wattage in an electrical circuit?
w=e times I
the electric meter on a house measures the ___________ passing through it
wattage
