Hvac ER PracticeTest
Which of the following is equal to 100 milliamps
0.10 amperes
Relays are generally used to control loads up to amps
10 amps
Three 300 ohm are wired in parallel. The total resistance equals
100 ohms
What is circuit resistance
All opposition to current flow
What is resistance?
All opposition to current flow
When checking the windings of a three phase motor?
All three terminals should show the same resistance.
How are fuses sized
Amps and Volts
A thermocouple can
Both A and B
Contactors are rated according to the maximum amperage through the?
Contacts
A heavy duty manually operated switch for three phase systems is a;
Disconnect
The symbol for current
E
Resistance can be calculated by
E divided by I
If contacts become dirty or pitted, it's acceptable to sand or file them as a permanent repair
False
Single phase motors are more efficient than three phase motors
False
When testing a motor with an ohmmeter one winding shows a 1000 ohm continuity to the motor frame. This is an indication of a good safety ground?
False
The capacitor start-capacitor run (CSCR) motor;
Provides high starting torque
Impedance in a circuit is the result of
Pure resistance Capacitive reactance Inductive reactance
A device used to control a motor
Relay Contactor Line starter
In a single phase motor, which winding has the most resistance
Start Winding
A 240 volt 3 wire circuit can be split into two 120 volt circuits
True
A three phase system requires a minimum of three supply lines to the three phase load
True
How many switches can be connected into contactor coil control circuit
Unlimited switches
To discharge a capacitor prior to ohmmeter testing
Use a 15,000 or 20,000 ohm, 2 to 5 watt resistor across the terminals
Transformers are rated according to?
VA at the secondary
Which of the following is the correct formula for determining wattage in an electrical circuit
W=E times I
The meter on a house measures the blank passing through it
Wattage
An electron has what kind of charge?
negative charge
The synochronus speed of a four pole, 60 Hz single phase motor is
1800 rpm
Which of the following is equal to 2.1 KV
2,100 Volts
How many watts are used by a heater at 460 volts operating at 5 amp
2300 watts
Utility companies usually supply residential homes with service
240 V , Single Phase, Three wire
A transformer has 1000 turns of wire in the primary and 2000 turns in the secondary coil. If 120 volts were applied the output voltage would be
240 volts
Three resistors are wired in parallel. Two of the resistors have a value of 12 ohms, one resistor has a value of 6 ohms. What is the total resistance of the circuit
3 ohms
Maximum allowable plus or minus supply voltage variation
5%
How much resistance must be placed in a 110 volt circuit in order to the limit the current to 2 amps
55 ohms
A parallel circuit contains an 18 ohm and a 9 ohm resistor. The total resistance equals;
6 ohms
A parallel circuit consists of three resistors R1=30 OHMS R2=15 OHMS R3=10 OHMS 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. If 120 volts were applied the output voltage would be
60 volts
One horsepower is equal to
746 watts
Three resistors are wired in series. Each has a value of 300 ohms. What is the total resistance of the circuit?
900 ohms
symbol for a thermal overload
A
Any material that will readily release electrons is called
A conductor
In electrical wiring a black wire represents
A hot conductor
An ohmmeter should never be connected to?
A live circuit
In a series circuit, the voltage drop across each resistance (Load) will;
All of the above
When replacing a capacitor
All of the above
When testing the windings of a single phase motor, Tech 1 says that the common and run terminals show the lowest resistance. Tech 2 says that the pair of terminals with the highest resistance will indicate that the other terminal is the common. Who's correct?
Both are correct
Two 120 voltmeters are wired in series one is a 60 watt motor the other is a 4 watt motor what would be the result
Both of the motors would not operate correctly
The terminals T1, T2, T3, are located at the of a contactor
Bottom
A capacitor opposes current flow in a circuit. This opposition is called
Capacitive reactance
A may be used on a single phase induction motor to disconnect the start winding after the motor starts
Centrifugal Switch Amperage Relay Potential Relay
To change direction of rotation of a three phase motor?
Change the position of any two start wires
Which of the following statements about current is true?
Current flow increases when voltage increases
When the temperature of a NTC thermistor increases, its resistance will
Decrease
Amperes can be calculated by
E divided by I W divided by E The square root of W divided by R
A solenoid valve operates on the principal of?
Electromagnetism
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
Overcurrent can be caused by;
Ground faults Short Circuits and overloads
Electricity can produce
Heat, light, and magnetism
What would be the result of 3 defrost heaters each 12.5 ohms Wired in series to 115 volt power supply if the heaters supplied a 360 watt heating load
Heaters do not energize
Voltage can be calculated by
I times R
Capacitors are always connected to the start winding
In series
When the temperature of a PTC thermistor increases, its resistance will
Increase
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 current flow a is produced around the conductor
Magnetic Field
The thermal overload contacts on a line starter are usually reset
Manual Reset
Capacitors are rated in?
Microfarads and Amperes
Tech 1 says that an open transformer coil is indicated by a reading of 0 ohms on an ohmmeter. Tech 2 says that a shorted transformer coil is indicated by a reading of infinity on an ohmmeter. Who's correct?
Neither Tech 1 or Tech 2
Single phase motor speed is determined by the?
Number of stater poles.
What meter is used to bench check a motor for shorts or open windings ?
Ohmmeter
What type of meter uses its own battery
Ohmmeter
The drawing illustrates where the components are located on the appliance
Pictorial drawing
A transducer can create a signal based on a form of energy such as
Pressure Heat and fluid flow
Term used to describe the output side of the transformer
Secondary Side
Direction of rotation of a single phase induction motor is determined by?
The direction of current flow through the start winding
When resistors are wired in parallel;
The voltage drop across each resistor will be the same as the applied source voltage
Fuses are used to protect?
Wires
symbol for transformer:
b
symbol for a pressure switch
c
When testing a capacitor with an analog the needle on the meter should?
deflect towards zero then return to infinite reading
step-up transformer
increases voltage
The total resistance of a parallel circuit will be
less than the smallest resistance
A capacitor analyzer is designed to;
read the microfarad rating of a capacitor
Like charges will
repel each other
What is current flow
the flow of electrons in the circuit