Electrical Test 1 Review
Define voltage
(E). The amount of electrical pressure in a circuit. Voltage is also known as electromotive force (EMF) or potential difference
What is three-phase AC voltage
A combination of three alternating voltage wave forms, each displaced 120 electrical degrees (1/3 of a cycle) apart. Produced when three coils are simultaneously rotated in a generator.
Define semiconductor
An electronic device that has electrical conductivity between that of a conductor and that of an insulator
What is the difference between an analog display and a digital display
Analog display- electromechanical device that indicates readings by the mechanical motion of a pointer. Digital Display- electronic device that displays readings as numerical values.
What is the purpose of a rectifier
Converts AC to DC by allowing the voltage and current to move only in 1 direction.
Compare and rate copper, silver, and aluminum conductors based on effectiveness and cost
Copper- great conductivity, decently expensive. Silver- excellent conductivity, really expensive. Aluminum- good conductivity, cheaper and lighter than copper.
Compare the voltage/current relationship with the current/resistance relationship
If Resistance stays constant, a change in current is directly proportional to a change in voltage. If Voltage stays constant, a change in resistance produces an inversely proportional change in current.
Identify the purpose of test lights
Primarily used to determine when voltage is present in a circuit, such as when testing receptacles.
List and describe the analog scale divisions
Primary Division- division with a listed value. Secondary Division- a division that divides primary divisions in halves, thirds, fourths, eighths, etc. Subdivision- Division that divides secondary divisions in halves, thirds, fourths, etc.
What is impedance
The combined opposition to the flow of current.
The power formula is the relationship between what three variables
The relationship between Power (P), Voltage (E), and Current (I).
Define heat
Thermal energy.
Define current
(I). The amount of electrons flowing through an electrical circuit.
How many valence electrons does a semiconductor have
4
What is a wrap-around bar graph
A bar graph that displays a fraction of the full range on the graph, the pointer wraps around and starts over when the limit of the bar graph is reached.
Define circuit
A complete path (When ON) for current to take and includes electrical control devices, circuit protection, conductors and loads
Differentiate between cycle and alternation
A cycle is one complete positive and negative alteration of a waveform. An Alteration is half of a cycle.
What is a heat sink
A device that conducts and dissipates heat away from a component.
Define ohmmeter
A device that is used to measure the amount of resistance in a component or circuit that is not powered.
What is the NFPA 70E
A safety code that helps companies avoid workplace injuries.
Describe the operation of series connected switches
All switches must be closed before current can flow. In series, if any switch opens the current will stop flowing.
Describe two types of tachometers
Contact- measures the rotational speed of an object through direct contact of the tip with the object being measured. Strobe- uses a flashing light to measure the speed of a moving object.
Ohm's law and the power formula are limited to circuits with only what type of opposition to current flow
Electrical resistance is the only significant opposition to the flow of current.
List and explain the three main parts of an atom
Electron- Negatively charged particle Neutron- Neutral particle, mass close to protons, exists in nucleus Proton- Positively charged particle, exists in nucleus
Give examples of materials that have good thermal conductivity and materials that have poor thermal conductivity
Good: solids like aluminum and copper. Bad: gas and liquids like air and water
What do the horizontal and vertical axes represent on a scope display
Horizontal- Time Vertical- Amplitude
Explain the power/current relationships
If Voltage stays constant and the power required changes, the current also changes.
Explain how to use a test light to determine if a receptacle is not grounded
If a test light illuminates when the test leads are connected to the neutral slot and hot slot but does not light when connected to the ground slot and hot slot, the receptacle is not grounded.
How can errors occur when reading a digital display
If the displayed prefixes, symbols and decimal points are not properly applied.
List 6 typical manually operated scope adjustment controls
Intensity Focus Horizontal Positioning Vertical Positioning Volts/division Time/division
Define in-phase
The state when voltage and current reach their maximum amplitude and zero level simultaneously.
Explain how to determine if a tool is double insulated
They have two prongs and have a notation on the specification plate
Explain which type of foot protection is appropriate when working on electrical equipment
Thick-soled rubber work shoes from protection against sharp objects and insulation against electrocution.
Why might a voltage indicator be used
Used to test receptacles, fuses, circuit breakers, cables and other devices in which the presence of voltage must be detected.
What is thermal conductivity
the property of a material to conduct heat in the form of thermal energy.
Define speed
the rate at which an object moves, measured in RPMs
Define power
(P). The rate of doing work or using energy.
How should an edged or sharply pointed tool be carried
Carry the tool with the cutting edge or the point down and outward from the body
What are some of the applications of Ohm's law
Design. Troubleshooting. Predict Characteristics
Why must cutting tools be sharp and clean
Dull edges cause us to exert extra force to cut, which can result in losing control of the tool
What is the NEC
National Electric Code
Explain how to calculate total resistance in a circuit containing series-connected loads
Rt = R1 + R2 + R3.......
Define peak value of a sine wave
(Vmax). The maximum value of either the positive or negative alternation.
What is a multifunction test instrument
A test instrument that is capable of measuring two or more quantities.
What is a test light
A test instrument that is designed to illuminate in the presence of 115V and 230V circuits. A brighter glow indicates a 230V circuit.
What is a continuity tester
A test instrument that is used to test a circuit for a complete path for current to flow.
Differentiate between an abbreviation and a symbol
Abbreviation- a letter or combination of letters that represents a word. Symbol- a graphic element that represents a quantity or unit.
What three factors influence the amount of increase in temperature
Amount of heat produced. Mass being heated. Material.
What is a transformer and how is it used
An electric device that uses electromagnetism to change (step up or step down) AC voltage from one level to another
Compare average value and root-mean-square value of a sine wave
Average Value of a sine wave is the mathematical mean of all instantaneous voltage values in the sine wave. RMS value is the value that produces the same amount of heat in a pure restive circuit as a DC current of the same value.
What values do digital multimeters measure
Basic DMMs measure resistance (continuity) and AC or DC voltage and current. Advanced DMMs measure frequency, capacitance and temperature as well as resistance and AC/DC voltage and current.
What is a BTU
British Thermal Unit - the amount of energy required to heat 1 pound of water 1 degrees Fahrenheit.
How are electrical insulations classified
By temperature ratings: 60°C 75°C 90°C
Describe the procedure for using a voltage tester
Check on known energized circuit to verify proper operation. Verify tester has proper voltage rating. Connect the common test lead to the point of testing. Connect the voltage test lead to the point of testing. Observe measurement and then remove tester.
What are the extinguishing agents for each class of fire
Class A- Water (green triangle) Class B- foam, CO2, dry chemical and halon (red square) Class C- CO2, dry chemical and halon (blue circle) Class D- Dry powdered compound (yellow star) Class K- Wet chemical
List the common classes of fires and where they occur
Class A- wood, clothing, paper, rubbish, etc. Class B- flammable liquids Class C- electrical equipment or facilities near electrical equipment Class D- combustible materials Class K- kitchens with grease
List different sources of energy
Coal, oil, gas, wood and nuclear power
Describe the two theories of current flow
Conventional current flow- flow from positive to negative. Electron current flow- flow from negative to positive.
How is current calculated using the power formula
Current (I) = Power (P) / Voltage (E)
Explain the difference between AC and DC voltage
DC flows in one direction only, AC reverses its direction of flow at regular intervals.
Which variable of the power formula would be easiest to calculate for electrical equipment
Determining expected current values because most electrical equipment lists a voltage and power rating.
List four safety rules for using test insturments
Do not test damaged instruments. Keep fingers behind finger guards. Before use, verify test leads are in proper jacks. Before measurement, verify the function of instrument matches what you are trying to test.
Compare inductance and capacitance
Inductance- the property of a circuit that causes it to oppose a change in current die to energy stored in a magnetic field. Capacitance- the ability of a component or circuit to store energy in the form of an electrical charge.
How can an in-line ammeter be used to measure current within a circuit
Inserting the test instrument in series with the components under test.
What is the purpose of a megohmmeter
It detects insulation deterioration
How many electrons can be held in each shell of an atom
K-2 L-8 M-18 N-32 O-50 P-72 Q-98
Define kinetic energy and explain its relationship to potential energy
Kinetic energy is the energy of motion. Kinetic energy is released potential energy
What is followed if local codes are stricter than the NEC
Local Code must be followed
Why must there be no voltage present in a circuit being tested for resistance
Low voltage gives us inaccurate readings, high voltage can cause equipment damage.
What is a conductor
Material that has very little resistance and permits electrons to move through it easily
Describe infrared meters
Measures heat energy by measuring the infrared energy that a material emits.
Describe clamp-on ammeters
Meter that measures current in a circuit by measuring the strength of the magnetic field around a conductor.
State Ohm's law
Ohm's law states that current in a circuit is proportional to the voltage and inversely proportional to the resistance.
List and describe two types of scopes used in troubleshooting
Oscilloscope- displays instantaneous voltage, in the shape of the waveform. Scopemeter- combo of oscilloscope and digital multimeter, displays the shape of a voltage waveform.
How does a parallel connection differ from a series connection
Parallel connections have more than one way for current to flow.
What is PPE
Personal protective equipment worn by an individual to reduce the possibility of injury in the work area.
How is power calculated using the power formula
Power (P) = Voltage (E) x Current (I)
List the safety rules to follow when using an in-lime ammeter
Power off before connecting. Do not change position during test. Turn off before changing settings.
List the safety rules to follow when handling power tools
Power tools must be inspected and serviced at regular intervals. Know all manufacturer safety rules. Inspect cords. Do not remove safety guards, make sure they work. Make all adjustments with power off. Make sure power is off on device before plugging in. Wear safety goggles and dust mask. No obstructions. Be attentive. Investigate change in sound immediately. Power off when work is complete. Remove defective tool from service. Do not operate around flammable materials. Unplug with plug, do not pull the cord.
List several different types of PPE
Protective clothing. Head protection. Eye protection. Ear protection. Hand and Foot protection. Knee protection. Rubber insulated matting
Why is it important for a tool system to be organized
Provides both a central location for retrieval and a means of protection during storage
What can be gained by measuring resistance in a circuit
Resistance measurements are normally taken to indicate the condition of a component of circuit. The higher the resistance, the lower the current flow. The lower the resistance, the higher the current flow.
Explain the difference between the 3 states of matter
Solid- definite volume and shape Liquid- definite volume no definite shape Gas- fluid, low density and highly compressible
Discuss the difference between static electricity and generated electricity
Static electricity is an electrical charge at rest. Generated electricity is the AC current created by power plant generators.
Explain how to calculate the frequency of a waveform
Step 1. Calculate Time Period Step 2. f = 1/T = Hz.
What causes ghost voltages
The magnetic fields generated by the current carrying conductors, fluorescent lighting, and operating electrical equipment.
Define Electricity
The movement of electrons from atom to atom
What determines whether an element allows electrons to move easily from atom to atom
The number of electrons in the valence shell
What part on an atom determines the atom's weight and atomic number
The number of protons in an atom
Define valence shell
The outermost shell of an atom and contains the electrons that form new compounds
Why is a scope sometimes more useful than a DMM when examining voltage
The scope shows the shape of the voltage and allows the voltage level, frequency and phase to be measured. A graphical display is more useful in some cases.
What are the functions of solenoids and colored plungers on voltage testers
The solenoids vibrate when the tester is connected to AC voltage. Colored plungers will indicate the polarity of test leads when measuring a DC circuit.
What must be verified before any repair is performed on a piece of electrical equipment
The source of electricity is locked out and tagged out
Identify why many test instruments include a fuse in the low-ampere range
To prevent damage caused by excessive current.
Differentiate between trace and sweep on a scope display
Trace- Reference point/line that is visually displayed on the face of the scope screen. Sweep- movement of the displayed trace across the scope screen.
Differentiate between true power and apparent power
True Power (Pt)- the actual power used in an electrical circuit. Apparent Power (Pa)- the product of the voltage and current in a circuit calculated without considering the phase shift that may be present between the voltage and current.
Write the equations for calculating voltage, current and resistance using Ohm's law
Voltage (E)= Current (I) x Resistance (R) Current (I) = Voltage (E)/Resistance (R) Resistance (R) = Voltage (E)/Current (I)
Why must safety precautions be taken when using a DMM
Wear PPE. Ensure no body part contacts live circuit. Exercise caution when measuring over 60V DC.
How does electric shock occur
When an individual comes in contact with two conductors of a circuit or when the body of an individual becomes part of an electric circuit.
What are the purposes of rubber insulating gloves and leather glove protectors
When working on energized circuits, rubber protects electrocution, leather protect the rubber from damage.
