Hbb Flashcards by Reed Hanus

Current flow is the;

B. flow of electrons in the circuit.

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Impedance is the measurement of the;

C. opposition to the flow of alternating current through a circuit.

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Like charges;

D. repel each other.

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Any material that will readily release electrons is called a/an;

A. conductor.

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The symbol for current is;

B. I.

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Which of the following materials would be used as a semi-conductor?

D. Silicon.

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The color of the safety ground wire is usually;

B. green or bare.

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An electron has:

A. a negative charge.

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Resistance is;

D. opposition to current flow.

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How many watts of power are used by a heater operating at 460-volts and drawing 5-amps?

D. 2,300 watts.

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Cooling anticipation is performed by the thermostat; during which cycle?

A. Off cycle.

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In electrical wiring, a black-colored wire in an alternating current circuit usually indicates which conductor?

B. Hot conductor.

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Fuses are sized by which parameters?

B. Volts & amps.

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If a 24-volt, 20-ohm low-voltage contactor coil were wired in series with a 24-volt, 200-ohm control relay coil, what would the result be?

C. Only the control relay would operate.

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Three (3) defrost heaters, each 15 ohms, are wired in parallel to a 120-volt power supply. How many watts of power will be used?

D. 2880 watts.

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Which of the following is generally considered to be within the maximum allowable (+/-) supply voltage variation for a 230-volt supply?

D. 219 to 242 volts

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Capacitors are rated in which units?

B. Microfarads & volts.

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How many diodes are used to make a bridge rectifier connected to a center tap 3-wire transformer?

B. 2

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What term is used to describe the output side of a transformer?

D. Secondary side.

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One horsepower is equal to how many watts?

C. 746 watts.

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How much resistance must be placed in a 120-volt circuit to limit the current to 2 amps?

A. 60 ohms

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What is the total resistance of a parallel circuit containing an 18-ohm and a 9-ohm resistor?

A. 6 ohms

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In a series circuit, what will the voltage drop across each resistance (load) do?

A. Add up to equal the source voltage.

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What will the total resistance of a parallel circuit be?

D. The sum of all resistances

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When will current flow increase?

D. When voltage increases.

When resistors are wired in parallel, what will be true about the voltage drop across each resistor?

D. The voltage drop across each resistor will depend on the value of each resistor.

2.1 kilowatts (KW) is equal to how many watts?

C. 2,100 watts

How does a Wi-Fi thermostat communicate with the network?

C. thermostat's IP and/or Mac address.

What does a capacitor analyzer measure?

A. The capacitance of a capacitor.

Which device changes the pressure signal in an electronic oil safety switch to an electrical signal?

D. Transducer

Heating anticipation is performed by a mechanical thermostat:

C. During the off cycle

A three phase load required a minimum of:

A. Three supply lines

The correct formula for determining wattage in an electrical circuit is:

A. W=EX|

A parallel circuit consist of three resistors R1= 30 ohms R2= 15 ohms R3=10 ohms If the correct through R2=4 amperes, what is the source voltage?

B. 60 volts

Three resistors, each 300 ohms, are wired in parallel. The total resistance equals

A. 100 ohms

An electronically commutated motor (ECM) used in an air handler is designed to:

D. Provide proper air flow under various conditions

Resistance can be calculated by:

A. E / I

How can voltage be calculated?

B. I x R

A multimeter set to measure resistance should never be connected to a/an:

A. charged capacitor until it has been discharged.

Which of the following is considered an inductive load?

B. Electric motor.

The voltage to group of a “high leg” on a three phase open Delta system will be approximately:

B. 208

A transformer has 1,000 turns in the primary coil and 500 turns in the secondary coil. If 120 volts are applied, what is the output voltage?

A. 60 volts.

A transformer has 1,000 turns in the primary coil and 2,000 turns in the secondary coil. If 120 volts are applied, what is the output voltage?

C. 240 volts.

Which of the following letter is the representation for impedance in an AC circuit?

D. Z.

When current flows in a two wire circuit (such as 120 V) if a clamp on an meter is clamped around both wires. What measurement would you expect?

D.Zero amps due to cancellation of the two fields.

If the conductor in an AC circuit is wound into a coil, the resulting EMF opposes the supply voltage this opposition is called

C. Inductive reactance.

A diode is used to

A. control the direction of electron flow.

What can be done to provide a common wire to an electronic thermostat when the existing cable cannot be replaced or when an additional wire cannot be installed?

D. An add-a-wire accessory can be used to take the place of terminals “y” and “G”

The direction of rotation of a single-phase induction motor is determined by the

B. direction of current flow through the start winding.

Single-phase motor speed is determined by the;

C. number of stator poles.

The capacitor start-capacitor run (CSCR) motor provides;

D. Medium running and high starting torque

To change direction of rotation of a three-phase motor;

B. change the position of any two supply wires.

Capacitors are always connected to the start winding;

B. in series.

Which function of a digital multimeter is used to bench check a motor for shorts or open windings?

B. Resistance

A solenoid valve coil operates on the principle of;

A. electromagnetism.

When checking the windings of a three-phase motor;

B. all three terminals should show the same resistance.

When testing the windings of a single-phase motor, the;

A. Common to run terminals will show the lowest resistance

A direct digital control (DDC) is a/an;

D. electronic control used for equipment operation and monitoring.

A step-up transformer increases;

D. voltage

Transformers are rated according to?

D. Volts-amps (VA) at the secondary

How many diodes are used to make a bridge rectifier connected to a 2-wire transformer?

D. 4

What connects to terminals T1, T2, & T3 on a contactor or motor starters?

B. Load connections

Circuit breakers and fuses are primarily used for?

A. protection from an overload of current.

Excessive current can be caused by?

B. a short circuit

A device with overload protection used to control a motor is a?

A. direct on-line starter

Relays are generally used to control inductive loads ranging between?

A. 1-15 amps

Contactors are rated according to the maximum amperage through the?

B. contacts

What is the minimum number of wires required between two mechanical start/stop push button controls?

B. 2

If contacts on a 30-amp contactor become badly pitted, it is acceptable to?

B. replace the contacts or contactor.

On a split-type heat pump system with an electronic data tube control, what is the minimum number of wires that need to be run between the indoor unit and the thermostat?

B. 4 wires

A drawing that illustrates where components are located and the wiring between these components in small appliances is a/an;

D. schematic diagram.

Which of the following motors has the highest energy efficiency?

A. ECM

On a good single-phase compressor motor, which winding terminals have the highest resistance?

A. Common to ground

When testing a motor winding for resistance, the following measurements are recorded: common to run 4 ohms, common to start 6.2 ohms, run to start 10.2 ohms, common to ground 20.4. These recorded measurements indicate a/an;

B. Grounded condition

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,

D. This is not a valid test

When the temperature of a negative temperature coefficient (NTC) thermistor increases, its resistance will;

A. decrease.

When the temperature of a positive temperature coefficient (PTC) thermistor increases, its resistance will;

B. increase.

The most common type of transducer used with HVAC equipment creates a signal based on;

A. pressure

a thermocouple can:

C. Generate a small DC electrical current

To discharge a capacitor prior to testing with a digital multimeter:

C. Use a 15,000 or 20,000 ohms, 2 to 5-watt resistor across the terminals

How is the common on electronic thermostats obtained with only 4 wires (R, G, W, Y) from the old heating and cooling thermostat?

D. The thermostat references common through an inactive circuit

The synchronous speed of a two pole, 60-Hz single-phase motor is

D. 3600 Rpm

Hbb Flashcards

(82 cards)