Vol 3: Test Equipment, Meters,and Grounding Flashcards
1
Q
How do analog meters differ from digital meters?
A
(1) Analog meters use a fixed scale and a needle movement, while digital meters use alphanumeric
displays.
(2) Digital meters typically have more options
2
Q
What questions should you ask yourself before using a meter? (List as many as you can.)
A
(1) Have I selected the correct meter and function for the property that I want to measure?
(2) Did I set the meter to the correct scale for the amount of the property I am measuring?
(3) How do I know that this meter is functioning properly?
(4) Do I trust the reading that this meter has given me? If not, why not?
(5) Have I taken the proper safety precautions associated with this particular meter?
(6) What protection did I provide myself in the event this meter fails?
(7) Am I wearing any conductive jewelry?
3
Q
In the “coin toss––you lose” scenario, what factors may have contributed to the accident?
A
(1) Rushing the job.
(2) Inexperience.
(3) Poor training.
(4) Lack of concentration.
(5) Too embarrassed to ask a question.
(6) Unfamiliar equipment.
4
Q
How is a voltmeter connected to the component or circuit being measured?
A
Connect the leads of the voltmeter in parallel with the item being measured
5
Q
What is meant by an “error of parallax”?
A
When you read a needle movement meter at an angle at other than 900. (Distance between the needle and
the scale causes error).
6
Q
How can you attain a more accurate reading on an analog voltmeter?
A
Lower the range progressively until the reading is in the upper 1/3 of the scale
7
Q
What can be used to bench check components that contain higher voltages than the basic meter is
capable of reading?
A
A high voltage probe.
8
Q
What is an important step when using analog ohmmeters that is not necessary with digital meters?
A
Zeroing the meter.
9
Q
To what should you never connect an ohmmeter?
A
An energized voltage source.
10
Q
For what are megohmmeters used?
A
Measuring resistance of insulation in millions of ohms
11
Q
What are the two ways that megohmmeters produce voltage?
A
A hand-crank that drives a small DC generator, or batteries.
12
Q
What are the two output voltages associated with megohmmeters?
A
500 and 1000 volts DC.
13
Q
What are ammeters designed to measure?
A
Current flow (amperage).
14
Q
List the safety precautions when using a clamp-on ammeter?
A
(1) Open jaws before changing scales.
(2) Do not exceed rating for the scale selected.
(3) Remove all jewelry.
(4) Use hot sticks when measuring high voltage.
15
Q
Multimeters typically measure which three properties?
A
Volts, amps, and ohms
16
Q
Explain how a voltage indicator shows the presence of voltage.
A
Depending on the type of voltage indicator, it will either cause a neon light to glow, or cause a spring loaded
pointer to move down a scale
17
Q
Which meter is more accurate: a voltmeter, or a voltage indicator?
A
A voltmeter is more accurate.
18
Q
What is the purpose of the phase rotation meter?
A
This meter determines phase sequence
19
Q
How are the leads on a rotation meter identified?
A
The leads are color coded and/or marked A-B-C
20
Q
What is the normal duration of a test using the recording meter?
A
24 hours.
21
Q
If the lines on the recording meter’s graph paper appear smudged, what corrective action should
you take?
A
Clean the pens.
22
Q
What do tachometers measure?
A
The speed of a rotating shaft.
23
Q
What action should you take before using an unfamiliar meter?
A
Read the manufacturer’s instructions.
24
Q
Explain what the MS–1A tester tests.
A
It tests current-actuated protective devices.
25
State the voltage requirements necessary for operation of the MS–1A tester.
110/120 volts, 60 cycle.
26
What is the acceptable tripping tolerance of a circuit breaker when tested?
Plus or minus 15 percent.
27
Where should you locate the transmitter for the circuit tracer?
Plug the transmitter into the duplex receptacle of the circuit you are tracing.
28
What are you looking for when you use the infrared detector?
You are looking for temperature rise or hot spots.
29
Where would you most likely use a gas detector meter?
Manholes, transformer vaults, subsurface structures, and splicing boxes.
30
What is the rating of the two high-impedance units that you use with the high-voltage phase
tester?
61/2 megohms each.
31
What happens if you keep the high-voltage phase tester connected to a live circuit for a long
period of time?
The resistors overheat.
32
What are the possible uses of the multicombination meter?
High-resistance voltmeter, ammeter and milliammeter, low-resistance voltmeter and millivoltmeter, and a
potentiometer voltmeter
33
Explain what the hot stick tester actually detects.
Moisture.
34
When you connect it to a ground, for what does the vibroground check?
It checks for ground resistance between the earth and the ground electrode.
35
How is a static ground defined?
It is a connection made between a piece of equipment and earth for the purpose of draining off static
electricity charges before a sparking potential is reached.
36
According to AFI 32–1065, what is the maximum acceptable ohmic reading for a static ground?
10,000 ohms.
37
What is meant by equipment grounding?
It pertains to the interconnecting and connection to earth of all noncurrent carrying metal parts on an
electrical wiring system, including equipment connected to the system.
38
What action must an equipment ground be capable of performing?
Carrying the maximum ground fault current possible without causing a fire or explosive hazard.
39
Explain the purpose of an electrical system ground.
To stabilize voltage to ground and give a low-impedance path for fault currents.
40
State the purpose of a lightning ground.
To safely dissipate lightning strokes into the earth.
41
Explain the good and poor points about the earth’s ability as a conductor.
The earth is considered a good conductor because there is so much of it; it is considered a bad conductor
because its resistivity is 10 billion times that of copper.
42
Which electrode earth shell has the highest resistance? Why?
The shell nearest the electrode has the highest resistance because it has the smallest circumferential area.
43
At what distance from a ground electrode to remote earth is resistance of approximately 68
percent encountered?
One foot.
44
When would you not use a pure copper ground rod?
Mechanical strength of copper is inadequate.
45
For what reason should stainless steel ground rods not be used?
They are too expensive.
46
Why should water mains not be used to ground connections?
There is a possibility water line maintenance or other work might result in accidental disconnection of the
grounding conductor to the equipment and create a hazardous condition.
47
Why is ground resistance more stable at a greater depth?
The soil is not affected as much by seasonal changes.
48
List four methods of obtaining better grounds.
(1) Deeper rod penetration.
(2) parallel ground rods.
(3) Soil replacement.
(4) Concrete encapsulation.
49
What is the makeup of the soil replacement mixture used to lower resistance of a ground rod?
Mix together 75 percent gypsum, 20 percent bentonite, and 5 percent sodium sulfate.
50
What usually causes grounding problems?
They are due mostly to violations of article 250 of the NEC.
51
Where are you required to ground the neutral conductor?
The source side of the service entrance disconnect.
52
What term can be used when referring to the neutral conductor?
The neutral conductor may be referred to as the grounded conductor.
53
What term can be used when referring to the bare or green insulated conductor?
This conductor is also known as the grounding conductor.
54
Which two areas of grounding are you referring to when you use the term grounding?
System grounding and equipment grounding.
55
Define the term system ground.
It is a connection to ground from one of the conductors of an electric circuit, normally the neutral
conductor.
56
Define the term equipment ground.
It is a connection to ground from noncurrent carrying metallic parts of the installation such as conduit and
equipment cases.
57
With what type of distribution system (wye or delta) should you use a grounded neutral
connection?
Wye.
58
Where should you ground the neutral for electrical power sources?
At the transformer secondaries and at the generators.
59
How often should the primary common neutral be grounded throughout the circuit?
At intervals not to exceed 1/4 mile.
60
Should you connect the primary neutral conductor together with the secondary neutral conductor?
Yes, if the neutral conductor is effectively grounded.
61
What are you limiting when you ground the secondary side of a wye-connected transformer?
Transient overvoltages.
62
Should the equipment ground and the system ground be tied together?
Yes, normally the two are interconnected at some point.
63
Is it good practice to drive a ground rod directly against a pole for grounding purposes? Why?
No. The soil around the rod may have become loose while setting the pole, resulting in higher resistivity.
Furthermore, the pole tends to cut off a large portion of the conduction path of the cylinder of earth which
surrounds the rod.
64
How far below the ground surface should you drive the top of a ground rod?
Two feet.
65
What is the requirement for a facility ground?
The facility’s wiring system must have a grounding electrode at each service.
66
Is it acceptable to use aluminum ground rods or aluminum ground plates?
No, per AFI 32–1065.
67
Does the Air Force permit the use of stainless steel ground rods?
No, per AFI 32–1065.
68
Name the two requirements for grounding computers.
The grounding for the power distribution system must follow NEC safety requirements. Also, the computer
equipment and enclosures must connect to a reference grounding system.
69
What is the purpose of the computer reference ground?
To eliminate high-frequency noise.
70
Where is the computer ground bonded?
To the electrical ground
71
Define a separately derived system.
It is a premises wiring system where power is derived from a generator, transformer, or a converter, and has
no direct electrical connection, including the neutral, to supply conductors originating in another system.
72
How would you make sure that a generator is a true separately derived system?
By ensuring the neutral conductor is not connected to the commercial power during, before or after a
transfer is made.
73
Why should you use an isolated ground on a receptacle when powering electronic equipment?
To reduce noise or static.
74
When you are installing a receptacle into a box, what conductors should not come in contact with
each other?
None of the conductors should come in contact with each other.
75
How long is a ground rod expected to last?
More than 20 years
76
What must be grounded on an isolation transformer?
The shield and core must be grounded to the transformer enclosure
77
Why should all conduit connections have tight fittings?
Because a major portion of the ground fault current returns over the conduit.
78
What term describes a situation where the yellow-green grounding conductor of an IG receptacle
is not connected?
Open ground circuit
79
What happens if you switch the neutral and ground connections?
The error can cause excessive current flow on the grounding conductor
80
Define ionization.
Ionization is the process of separating air molecules into positive ions and negative electrons
81
Explain why lightning discharges don’t always bring electrons to Earth
Because so-called positive ground-to-cloud strokes consist of low power energy transmissions from Earth
to small negative charge pockets in a thunder cloud.
82
What happens to the air once it is ionized?
The air becomes a good conductor and allows the cloud electrons to pierce the faulted insulation and
descend the newly created ionized air path between cloud and Earth.
83
What occurs once the stepped leader from a thundercloud and the ionized streamer from the Earth
join?
Electrons pour from the lightning discharge channel creating a brilliant lightning stroke.
84
What can happen if lightning protection systems are grounded poorly?
A high voltage is impressed between the down conductor and earth, resulting in a possible explosion or
damage to system.
85
Lightning strikes three to 20 miles away are capable of doing what to ungrounded equipment?
Inducing up to 60,000 volts on to the equipment.
86
Materials used to provide lightning protection conform to what code and or standards?
NFPA codes 70 and 780 as well as UL standards 96 and 96A.
87
What type of materials will normally be specified for use below finished grade?
Normally, copper materials.
88
What requirements must be met when compression-type connectors are used in lightning
protection systems?
UL listed compression-type connectors may be used where such connectors are equivalent to the welded
type.
89
How deep should the main counterpoise be installed?
At least two feet below finished grade and will extend beyond the building perimeter not less than three nor
more than eight feet.
90
How deep are ground rods driven when they are connected to the main counterpoise?
At least 6 inches below normal ground water table level, where earth is available for driving
91
Explain how lightning follows a path to ground.
Lightning takes the path of lowest impedance to ground.
92
What types of materials are used for buildings under 75 feet in height?
Class 1 materials.
93
Air terminals should be installed within how many inches of each ridge? How many feet between
intervals?
24 inches. Less than 25 feet apart.
94
What is the minimum bend radius of a conductor in a lightning protection system?
Minimum of an 8-inch radius.
95
Lightning protection systems must conform to which NFPA standard?
NFPA No. 780.
96
What is the maximum distance from the grounding system that conductive objects must be
interconnected in order to provide a common ground potential?
25 feet
97
What size ground rods are used in lightning protection systems?
They will be not less than 10 feet in length or less than 3/4-inch diameter pipe or equivalent solid rod
98
How close to the perimeter of the building foundation are ground rods driven?
Three to eight feet beyond perimeter of the building foundation.
99
How deep are ground rods driven, as a minimum, in a lightning protection system?
Rods are driven so that the tops are at least 6 inches below finished grade.
100
What size conductor is used for the counterpoise?
It consists of one or more closed loops or grid arrangement of No. 1/0 AWG bare copper conductors
installed around facility perimeter.
101
How deep must the counterpoise be buried?
Not less than 2 feet below earth surface.
102
What size conductor is used in a radial system of grounding?
No. 1/0 AWG copper conductors.
103
In which direction from the grounding connection must the radials extend?
Extend away from each ground rod or grounding connection.
104
What is the objective of static electricity protection?
To provide a means whereby static electricity charges, separated by whatever cause, may recombine
harmlessly before sparking charges are attained.
105
How are electrostatic electricity charges generated?
By friction or contact between dissimilar conductive, semiconductive, or nonconductive moving objects,
materials, liquids, or air particles.
106
What minimum sparking voltage at sea level is generally accepted for the shortest measurable
length of gap?
Approximately 350 volts for the shortest measurable length of gap.
107
What is the usual way to dissipate or reduce unwanted electrical charges in hazardous areas?
By providing a continuous electrical path to ground
108
Since the grounding path’s resistance can be relatively high, what is the most important aspect of
a static grounding system?
Mechanical strength and reliability of conductors and connectors.
109
What is bonding?
The process of connecting two or more conductive objects together by means of a conductor.
110
What must you do before securing any bond?
Remove any paint, oil, dirt, or rust so you have an electrically clean contact surface.
111
Where are the grounding conductors that are provided for connection to grounding electrodes
located?
Opposite corners of any building.
112
Under what condition can steel framing members of the building be used as part of the static
grounding conductor system?
Steel framing members of the building and metal sides electrically bonded and not used for lightning
protection may be part of the static grounding conductor system.
113
What size and type of ground conductor is used on fuel storage tanks?
1/4- to 3/8-inch galvanized guy wires.
114
How many ground rods do you need on a fuel storage tank with a 450-foot circumference?
Five ground rods.
115
When does a metal fence require no additional grounding?
If it is electrically continuous with metal posts extending at least two feet into the ground.
116
When are rail spurs bonded and grounded?
Rails extending within 100 feet of a facility that is used for storing, manufacturing, processing, or handling
explosives or flammable liquids.
117
When you use cathodic protection on a hydrant fueling system, what must you do to isolate the
ground from the cathodic protection system?
The outlet must be electrically isolated from the piping system at the first pair of flanges below the outlet.
118
What type of ground rod do you use on a hydrant fueling system?
A galvanized steel ground rod.
119
What is the minimum size ground rod for a truck fill stand?
A minimum of 5/8 inch in diameter and 8 feet long.
120
What size and type of conductor can you use to interconnect a truck fill stand and the ground rod?
No. 4 AWG stranded copper. When a replacement is necessary or new ground system is installed, use 3/32-
inch stainless steel wire rope that has a nylon cover.
121
What kind of conductor do you use to interconnect the grounding assembly and the static ground
rod on a truck fill stand?
A 1/0 AWG or larger copper wire.
122
Who visually inspects ground connection points in a POL area?
Liquid fuel maintenance personnel.
123
How often are insulated rail joints inspected?
Monthly
124
How often are static ground rods tested?
Only when installed or physically damaged
125
What parts of buildings must have lightning protection?
Chimneys, ventilators, tower domes, ridges, and other high points that project above the buildings’
surroundings
126
Name the main parts of a lightning protection system.
Air terminals, a system of ground terminals, with a conductor system connecting the two.
127
When does a metal building not need a lightning protection system installed?
When buildings are made of metal parts at least 3/16 inch thick and electrically continuous.
128
How far must an air terminal extend above the object it is to protect?
A minimum of 10 inches; 24 inches for explosive facilities.
129
What is the maximum distance between down conductors?
100 ft
130
Why are ground wells needed and what is used to create the well?
To aid in the testing of ground systems; a pipe or concrete lining.
131
What type of lightning protection system is required for new explosive storage facilities with a
perimeter over 300 feet?
A mast system or an overhead wire system.
132
Describe an overhead wire system.
A lightning protection system that consists of grounded, elevated horizontal metallic wires stretched
between masts surrounding the facility.
133
If air terminals are placed on large flat roofs, what modifications do you make to their
installation?
Increase their height to four feet above structural parts, ridges, or the roof’s edge, and you can increase the
spacing between terminals to 25 feet.
134
What are the minimum number of down conductors required on an explosive storage facility and
where are they located?
Not less than two down conductors located as widely separated as practicable, preferably at diagonally
opposite corners.
135
What size wire do ground loop conductors use? At what depth are ground loop conductors
buried?
1/0 AWG; at least two feet below the earth’s surface.
136
Where are static busbars installed?
On the interior wall of a facility.
137
Describe the test electrode used to test conductive floors.
Each electrode must weigh five pounds and have a dry, flat circular surface area 21/2 inches in diameter.
138
Name the three main functions of communication facility grounding systems.
Personal safety, equipment protection, and noise reduction.
139
What minimum size ground rods are used in communication facility areas?
10 feet long and 3/4 inch in diameter.
140
Where are plate electrodes used?
In small areas where grids and ground rods are impractical
141
Name two types of horizontal conductor ground system configurations.
Any two of the following: Ground loop, star ground, rebars, metal water pipe, or metal fence posts.
142
Conductors used to interconnect earth electrodes must meet what requirement?
Must be at least 1/0 AWG stranded copper and continuous (splice free or welded).
143
What zone of protection ratio do communication facilities require?
1:1 ratio.
144
What is the minimum height of the poles that support overhead ground wires protecting a
communication facility?
They must be sufficient to provide a clearance of at least 6 feet between the overhead wire and the highest
part of the building.
145
How do power distribution arresters differ from their communication circuit arrester
counterparts?
Lightning arresters used in power distribution systems are physically larger and have higher energy
handling capabilities than those used in communication circuits.
146
Where are secondary arresters usually placed?
In power distribution cabinets.
147
What grounding protection is required for all towers and radio facilities?
A ground loop consisting of ground rods interconnected with a minimum 1/0 AWG bare copper cable.
148
On large towers, what is the maximum distance between down conductors at the tower base?
100 feet.
149
What type of lightning arresters do you use to protect antennas?
Horn-gap or gas-gap.
150
What are you checking for when performing the visual and electrical inspection of ground
systems?
Integrity of the system.
151
What must be done before you make any tests or repairs on a ground system in an explosive
storage facility?
Have the using agency remove all exposed explosives that may ignite.
152
List four items inspected during a visual check of a grounding system.
Any four of the below:
(1) The system is in good repair.
(2) There are no loose connections.
(3) Corrosion or vibration has not weakened any part of the system.
(4) All down conductors and terminals are intact.
(5) All conductors and components are securely fastened.
(6) There have been no alterations to the protected structure that would require additional protection.
(7) Any visual indication of damage to surge suppressio
153
What agency is responsible for conducting each of the checks below?
(a) Visual.
(b) Resistance.
(c) Continuity.
(1) The using shop.
(2) Base Civil Engineering electrical shop.
(3) The user or electric shop personnel.
154
What type of ground record should each facility have?
A sketch of the grounding system and documentation of all inspections and tests.
155
Describe how a continuity check is performed on a separately mounted lightning protection
system.
Connect one lead of a digital ohmmeter to the highest point on the pole or at the overhead shield wire
connection. Connect the other lead to the ground rod at the base of the pole. If the resistance is not
practically zero, check for deficiencies and make repairs. Visually inspect overhead wires with binoculars.
156
Describe the procedure for testing static busbars.
Connect one lead of a digital ohmmeter to a ground rod of the facility ground system. Connect the other
lead (in turn) to all the free ends of the busbar
157
What is the resistance check requirement for a communication facility?
It requires a quarterly resistance check for 1 year after initial ground installation, 10 ohms maximum. After
the first year, the requirement is every 21 months.
158
What is the visual and testing requirement for a weapon storage facilities lightning protection
system?
A visual inspection every seven months, continuity and resistance checks every 14 months, 10 ohms
maximum.
