Electricity HVAC

when current flows in a 2 wire circuit such as 120v, if a clamp on amp meter is clamped around both wires what measurment would you expect.

0 amps - due to cancellation of 2 fields

Which of the following is equal to 100 milliamps

0.10 amps

Relays are generally used to control inductive loads up to?

10 Amps

300 ohm resistors are wired in parallel. The total resistance equals

100 ohms

Which of the following is generally considered to be within the maximum allowable supply voltage variation

15%

Voltage to a ground of a high leg or stinger leg on a three-phase open Delta system will be approximately

208

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 amps

A transformer has 1000 turns of wire and a 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, 3-phase, 3-wire

3 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

What is the minimum number of wires required between to start / stop push-button controls

3

A 3-phase load requires a minimum of

3 supply lines

The synchronous speed of a 4 pole, 60 hertz single phase motor is

3600 RPM

Which of the following is an acceptable temporary replacement for a run capacitor rated at 35 MFD at 440 VAC

37.5 MFD at 440 VAC

Parallel circuit contains an 18 ohm and a 9 ohm resistor. The total resistance equals

6 ohms

how much resistance must be placed in 120V curcuit in order to limit the current to 2Amps

60 Ohms

A parallel circuit consists of three resistors. R1 equals 30 ohms, are two is equal to 15 ohms, are 3 is equal to 10 ohms. If the current through r2 is 4 amperes, what is the source voltage

60 volts

the transformer has 1000 turns of wire in the primary coil and 5000 turns in the secondary coil. If 120 volts are applied the output voltage will be

60 volts

One horsepower is equal to

746 watts

Any material that will readily release electrons is called

A conductor

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. Common to ground 20.4; this indicates a

A grounded condition

And electron has

A positive charge

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 motor

All few terminal should show the same resistance

The electric meter on a house measures the______passing through it

Amperage

An ohmmeter should never be connected to a

Charge capacitor and until it has been discharged

Contactors are rated according to the maximum amperage through the?

Contacts.

A diode is used to

Control the direction of electron flow

Which of the following statements about current is true

Current flow will decrease when voltage increases

A __________ is commonly used on a single phase fractional horsepower capacitor motor to disconnect the start winding after the motor starts

Current relay

When the temperature of a negative temperature coefficient thermistor increases, its resistance will

Decrease

Resistance can be calculated by

E / I

Which of the following motors is most energy efficient

ECM

Which of the following would be considered an inductive load

Electric motor

A solenoid valve operates on the principle of

Electromagnetism

Direct digital control is

Electronic controls used for equipment operation and monitoring

A thermocouple can

Generate a small DC electrical current

With a motor running at full load, voltmeter leads are placed on l1 and T12 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 which colors

Green or bare

The symbol for current is

I

Voltage can be calculated by

I x r

Capacitors are always connected_____ to the start winding

In series

When the Positive Temp coeffiecent thermistor increases, its resistance will

Increase

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

Inductive reactance

The total resistance of a parallel circuit will be

Less than the smallest resistance

Pair device with overload protection Hughes control a motor is a

Line starter

What connects to the terminal t1, t2, and t3 on a contactor or motor starter?

Load connections

The thermal overload contacts on a line starter are usually______reset

Manual

When testing a capacitor with an analog or digital ohmmeter, the meter should

Measure low Resistance then return to a high reading

Capacitor start capacitor run motor provides

Medium running and high starting torque

Capacitors are rated in

Microfarads and volts

Single phase motor speed AC termond by the

Number of stator poles

Which of the following meters must use its internal power to check a load or circuit

Ohm meter

Which meter is used to bench check a motor for shorts or open windings?

Ohmmeter

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

Only a control relay would operate

Resistance is

Opposition to current flow

Impedence is?

Oppostion to Alternating current flow.

The ________ Drawing illustrates where the components are located in small appliances

Pictorial

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

Pressure

Circuit breakers and fuses are primarily used to provide

Protection from an overload of current

An electronically commmutated motor (ECM) is designed to?

Provide proper airflow under various conditions

Like charges

Repel each other

If contacts become badly pitted, it is acceptable to?

Replace the contacts or control.

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

Run to start

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

Secondary side

Which of the following materials would be best suited for use as a semiconductor

Silicon

A capacitor analyzer is designed to

The capacitance of a capacitor

When testing the windings of a single phase motor

The common to start terminal show the lowest resistance

Direction of rotation of a single phase induction motor is determined by

The direction of current flow to the start winding

Current flow is?

The flow of electrons in the circuit.

In electrical wiring, a black colored wire in an alternating current circuit usually indicates

The hot conductor

When resistors are wired in parallel:

The voltage drop across each resistor will be the same as the applied source voltage.

I'm in electrical oil safety switch, what changes the pressure signal to electrical signal

Transducer

How to discharge a capacitor prior to ohm meter testing

Use a 15000 or 20000 ohm, 225 watt resistor across the terminals

Transformers are rated according to

VA at the secondary

Fuses are sized by

Volts and amps

Which of the following is the correct formula for determining wattage in a electrical circuit

W=E times I

To change direction of rotation of a 3-phase motor

You must change the position of any two supply wires

What is the symbol for impedence in an AC CIrcuit.

Z

Excessive current can be caused by

short circuit

Step up transformer increases

voltage