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