Electrical Theory & Application for HVACR
Which of the following is equal to 100 milliamps?
0.10 amperes
Relays are generally used to control inductive loads up to _____ amps.
10
Which of the following is an acceptable temporary replacement for a run capacitor rated at 35MFD @ 440VAC; - 50 MFD @ 370VAC - 47.5MFD @ 440VAC - two 20 MFD @ 440VAC in series - 37.5 MFD @ 440VAC
37.5 MFD @ 440VAC
The symbol for a thermal overload is represented by:
D
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 windings of a three phase motr;
all three terminals should show the same resistance
When the temperature of a negative temperature coefficient (NTC) thermistor increases, its resistance will;
decrease
Circuit fuses and breakers are primarily used to protect;
wiring
The synchronous speed of a four pole, 60 Hz single phase motor is;
1800 rpm
The voltage to ground of a "high Leg" on a three phase open Delta system will be approximately;
208
One horsepower is equal to _____ watts.
746
Resistance can be calculated by;
E divided by I
The symbol for current is...
I
What is the term used to describe the output side of a transformer?
Secondary side
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 x I
The electric meter on a house measures the __________ passing through it.
Wattage
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.
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.
A diode is used to
control the direction of electron flow
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
Which meter is used to bench check a motor for shorts or open windings?
ohmmeter
Like charges...
repel each other.
Excessive current can be caused by;
short circuit
When resistors are wired in parallel;
the voltage drop across each resistor will depend on the value of each resistor.
A three phase load required a minimum of;
three supply lines
The terminals T1, T2, & T3 are located at the ________ of a contactor.
top
To discharge a capacitor prior to ohmmeter testing;
use a 15,000 or 20,000 ohm, 2 to 5 watt resistor across the terminals.
A step up transformer increases;
voltage.
Fuses are sized by...
volts & amps.
The symbol for a transformer is represented by:
B
The symbol for a pressure switch is represented by:
C
Which of the following statements about current is true?
Current flow will increase when voltage increases.
Which of the following motors is most energy efficient? -SIRC -ECM -PSC -Shaded Pole
ECM
Which of the following would be considered an inductive load?
Electric motor
A 240 volt, 3 wire circuit can be split into two 120 volt circuits. (T or F)
False
The total resistance of a parallel circuit will be;
Less than the smallest resistance
Capacitors are rated in:
Microfarads & Volts
To change direction of rotation of a three phase motor;
change the position of any two supply wires
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
A solenoid valve coil operates on the principle of;
electromagnetism
Which of the following is NOT a factor in determining Impedance in an AC circuit? -resistance -inductive reactance -capacitive reactance -frequency
frequency
The thermal overload contacts on a line starter are usually ______ reset.
manual
The ___________ drawing illustrates where the components are located in small appliances.
pictorial
A transducer can create a signal based on;
pressure
In a single phase motor, which winding has the most resistance?
start
A capacitoor analyzer is designed to read;
the capacitance of a capacitor
Three 300 ohm resistors are wired in parallel. The total resistance equals;
100 ohms
Which of the following is equal to 2.1 KW
2100 Watts
How many watts of power are used by a heater operating at 460 volts and drawing 5 amps?
2300 watts (V x A = W)
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
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 (I x E = P)
What is the minimum number of wires required between two Start/Stop push button controls?
3
What is generally considered to be within the maximum allowable (plus or minus) supply voltage variation?
5%
How much resistance must be placed in a 120 volt circuit in order to limit the current to 2 amps?
60 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 are applied, the output voltage will be;
60 volts
A parallel circuit contains an 18 ohm and a 9 ohm resistor. The total resistance equals;
8 Ohms
Voltage can be calculated by;
I times R
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.
Neither technician #1 nor #2.
What type of meter uses its own battery?
Ohmmeter
If contacts become badly pitted, it is acceptable to;
Replace the contacts or control
Contactors are rated according to the maximum amperage through the;
contacts
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 the 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 capacitor start-capacitor run (CSCR) motor provides;
high starting and running torque
Capacitors are always connected __________________ to the start winding.
in series
When the temperature of a positive temperature coefficient (PTC) thermistor increases, its resistance ewill;
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
Single phase motor speed is determined by the;
number of stator poles
Impedance is...
opposition to alternating current flow.
Resistance is...
opposition to current flow.
An electronically commutated motor (ECM) is designed to....
provide proper air flow under various conditions.
Which of the following materials would be best suited for use as a semi-conductor?
silicone
When testing the windings 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.
Current flow is...
the flow of electrons in the circuit.
In electrical wiring, a black colored wire usually indicates...
the hot conductor.
