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Electrical HVAC excellence
Terms in this set (100)
Current flow is:
The flow of electrons in the circuit.
Opposition to alternating current flow.
repel each other.
Any material that will readily release electrons is called;
The symbol for current is;
Which of the following materials would be best suited for use as a semi-conductor?
The safety ground conductor is usually color coded;
green or bare.
An electron has;
a negative charge.
Opposition to current flow.
How many watts of power are used by a heater operating at 240 volts and drawing 5 amps?
Which of the following meters must use its internal power to check a load or circuit?
In electrical wiring, a black colored wire in an alternating current circuit usually indicates;
the hot conductor.
Fuses are sized by:
Volts & Amps
What would be the result, if a 24 volt, 20-ohm low voltage conta ctor coil were wired in series with a 24 volt, 200-ohm control relay coil?
Only the control relay would operate.
Three defrost heaters, each 15 ohms are wired in parallel to a 120 volt power supply. How many watts of power will be used?
Which of the following is generally considered to be within the maximum allowable (plus or minus) supply voltage variation?
Capacitors are rated in
Microfarads & Volts.
When testing a capacitor with an analog or digital ohmmeter, the meter should;
measure low resistance then return to high reading.
What is the term used to describe the output side of a transformer?
One horsepower is equal to __________ watts.
How much resistance must be placed in a 120 volt circuit the current to 2 amps?
A parallel circuit contains a 18 ohm and a 9 ohm resistor. The total resistance equals;
In a series circuit, the voltage drop across each resistance (load) will.
add up to equal the source voltage.
The total resistance of a parallel circuit will be;
less than the smallest resistance.
Which of the following statements about current is true?
Current flow will increase when voltage increases.
When resistors are wired in parallel;
the voltage drop across each resistor will be the same as the applied source
Which of the following is equal to 2.1KW?
Which of the following is equal to 100 milliamps?
A capacitor analyzer is designed to read;
the capacitive resistance of a capacitor.
On an electronic oil safety switch what changes the pressure singal to electrical signal?
The electric meter on a house measures the ______________ passing th rough it.
A three phase load requires a minimum of;
three supply lines.
Which of the following is the correct formula for determining wattage in an electrical circuit?
W = E times I
A parallel circuit consists of three resistors.
Three 300 ohm resistors are wired in parallel. The total resistan ce equals;
An electronically commutated motor (ECM) is designed to;
provide proper air flow under various conditions.
Resistance can be calculated by:
E divided by I.
divided Voltage can be calculated by;
I times R
An ohmmeter should never be connected to;
a charged capacitor until it has been discharged.
Which of the following would be considered an inductive load?
The voltage to ground of a "high Leg" or "Stinger Leg" on a three phase open Delta system will be approximately;
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.
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;
Which of the following is the symbol for Impedance in an AC circuit?
When current flows in a two wire circuit (such as 120 volts) if a clamp on amp meter is clamped around both wires. What measurement would you expect?
Zero amps due to cancelation of the two fields.
If the conductor in an AÇ circuit is wound into a coil, the resulting EMF opposes the supply voltage. This opposition is called.
A diode is used to;
control the direction of electron flow.
A ___________ is commonly used on a single phase capacitor start fractional horse power compressor motor to disconnect the start winding after the motor starts.
Direction of rotation of a single phase induction motor is determined by.
the direction of current flow through the start winding.
Single phase motor speed is determined by the.
number of stator poles.
The capacitor start-capacitor run (CSCR) motor provides;
high starting and running torque.
To change direction of rotation of a three phase motor.
change the position of any two supply wires.
Capacitors are always connected _____________ to the start winding.
Which meter is used to bench check a motor for shorts or open windings?
A solenoid valve coil operates on the principle of
When checking the windings of a three phase motor;
all three terminals should show the same resistance.
When testing the windings of a single phase motor,
the common to run terminals show the lowest resistance.
Direct Digital Control (DDC) is
electronic controls use for equipment operation and monitoring
A step up transformer increases;
Transformers are rated according to;
VA at the secondary.
Utility companies usually supply residential homes with ______________ service.
240V, single phase, three wire
What connects to the terminals T1, T2, & T3 on a contactor or motor starter?
Circuit breakers & fuses are primarily used to provide;
protection from an overload of current.
Excessive current can be caused by;
A device with overload protection used to control a motor is a;
Relays are generally used to control inductive loads up to __________ amps.
Contactors are rated according to the maximum amperage through the;
What is the minimum number of wires required between two Start/Stop push button controls?
If contacts become badly pitted, it is acceptable to.
replace the contacts or control
The thermal overload contacts on a line starter are usually_______________ reset.
The ______________ drawing illustrates where the components are located in small appliances.
Which of the following motors is most energy efficient.
On a good single-phase compressor motor, which winding terminals have the highest resistance?
run to start.
When testing a motor with an ohmmeter, the following measurements are recorded, Common to run 4 ohms, Common to start 6.2 ohms, Run to start 10.2 ohms, and Common to ground 20.4; This indicates a/an;
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.
When the temperature of a negative temperature coefficient (NTC) thermistor increases, its resistance will.
When the temperature of a positive temperature coefficient (PTC) thermistor increases, its resistance wilI;
A transducer can create a signal based on.
A typical thermocouple used on a gas furnace can.
generate a small DC electrical current.
To discharge a capacitor prior to ohmmeter testing.
use a 15,000 or 20,000 ohm, 2 to 5 watt resistor across the terminals.
Which of the following is an acceptable temporary replacement for a run capacitor rated at 35MFD @ 440VAC
37.5MFD @ 440VAC.
The synchronous speed of a four pole, 60 Hz single phase motor is;
The symbol for a heating thermostat is represented by diagram.
The symbol for a pressure switch that closes on pressure rise represented by diagram
The symbol for a pressure switch that opens on pressure rise is represented by diagram.
In the schematic, what voltage would be found across L1 to L2?
In the schematic, what voltage would be found across the condenser fan motor?
In the schematic, what voltage would be found across the transformer primary?
In the schematic, what voltage would be found across the fuse in line #10 with the thermostat closed?
In the schematic, what voltage would be found from terminal G to the load side of the transformer?
In the schematic, what voltage would be found across the contacts when energized in line #8
In the schematic, what voltage would be found from terminal Y to the input side of the coil on line #11?
In the schematic, what voltage would be found from terminal Y to the output side of the coil on line #11?
When troubleshooting the A/C system in the schematic, the following conditions are found. The thermostat contacts are closed. The compressor and condenser fan motors are short cycling. The blower motor is not running. This could be caused by.
a faulty blower motor or blower relay.
When troubleshooting the A/C system in the schematic, the following conditions are found. The thermostat contacts are closed. The compressor and condenser fan are not running. The blower motor is running. This could be caused by.
the HP, LP, overloads, or oil pressure switch are open (line #11).
When troubleshooting the A/C system in the schematic, the following conditions are found. The thermostat contacts are closed. The compressor and condenser fan motors are short cycling. The blower motor is not running. When the fan switch at the thermostat is moved from the AUTO position to the FAN ON position, the blower runs. This could be caused by.
a faulty thermostat - AUTO / FAN ON switch.
In the schematic, the crankcase heater will operate;
when the compressor is off.
in the schematic, the coil on line #11 does NOT control.
the blower motor.
In the schematic, the coil on line #12 controls the.
blower motor relay.
In the schematic, if the fuse in L2 is blown the.
blower motor will continue to operate.
Recommended textbook explanations
Mechanics of Materials
Engineering Mechanics: Statics
Thermodynamics: An Engineering Approach
Yunus A. Cengel
Engineering Mechanics: Statics
J.L. Meriam, L.G. Kraige
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