Vol 3: Test Equipment, Meters,and Grounding Flashcards
How do analog meters differ from digital meters?
(1) Analog meters use a fixed scale and a needle movement, while digital meters use alphanumeric
displays.
(2) Digital meters typically have more options
What questions should you ask yourself before using a meter? (List as many as you can.)
(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?
In the “coin toss––you lose” scenario, what factors may have contributed to the accident?
(1) Rushing the job.
(2) Inexperience.
(3) Poor training.
(4) Lack of concentration.
(5) Too embarrassed to ask a question.
(6) Unfamiliar equipment.
How is a voltmeter connected to the component or circuit being measured?
Connect the leads of the voltmeter in parallel with the item being measured
What is meant by an “error of parallax”?
When you read a needle movement meter at an angle at other than 900. (Distance between the needle and
the scale causes error).
How can you attain a more accurate reading on an analog voltmeter?
Lower the range progressively until the reading is in the upper 1/3 of the scale
What can be used to bench check components that contain higher voltages than the basic meter is
capable of reading?
A high voltage probe.
What is an important step when using analog ohmmeters that is not necessary with digital meters?
Zeroing the meter.
To what should you never connect an ohmmeter?
An energized voltage source.
For what are megohmmeters used?
Measuring resistance of insulation in millions of ohms
What are the two ways that megohmmeters produce voltage?
A hand-crank that drives a small DC generator, or batteries.
What are the two output voltages associated with megohmmeters?
500 and 1000 volts DC.
What are ammeters designed to measure?
Current flow (amperage).
List the safety precautions when using a clamp-on ammeter?
(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.
Multimeters typically measure which three properties?
Volts, amps, and ohms
Explain how a voltage indicator shows the presence of voltage.
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
Which meter is more accurate: a voltmeter, or a voltage indicator?
A voltmeter is more accurate.
What is the purpose of the phase rotation meter?
This meter determines phase sequence
How are the leads on a rotation meter identified?
The leads are color coded and/or marked A-B-C
What is the normal duration of a test using the recording meter?
24 hours.
If the lines on the recording meter’s graph paper appear smudged, what corrective action should
you take?
Clean the pens.
What do tachometers measure?
The speed of a rotating shaft.
What action should you take before using an unfamiliar meter?
Read the manufacturer’s instructions.
Explain what the MS–1A tester tests.
It tests current-actuated protective devices.
State the voltage requirements necessary for operation of the MS–1A tester.
110/120 volts, 60 cycle.
What is the acceptable tripping tolerance of a circuit breaker when tested?
Plus or minus 15 percent.
Where should you locate the transmitter for the circuit tracer?
Plug the transmitter into the duplex receptacle of the circuit you are tracing.
What are you looking for when you use the infrared detector?
You are looking for temperature rise or hot spots.
Where would you most likely use a gas detector meter?
Manholes, transformer vaults, subsurface structures, and splicing boxes.
What is the rating of the two high-impedance units that you use with the high-voltage phase
tester?
61/2 megohms each.
What happens if you keep the high-voltage phase tester connected to a live circuit for a long
period of time?
The resistors overheat.
What are the possible uses of the multicombination meter?
High-resistance voltmeter, ammeter and milliammeter, low-resistance voltmeter and millivoltmeter, and a
potentiometer voltmeter
Explain what the hot stick tester actually detects.
Moisture.
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.
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.
According to AFI 32–1065, what is the maximum acceptable ohmic reading for a static ground?
10,000 ohms.
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.
What action must an equipment ground be capable of performing?
Carrying the maximum ground fault current possible without causing a fire or explosive hazard.
Explain the purpose of an electrical system ground.
To stabilize voltage to ground and give a low-impedance path for fault currents.
State the purpose of a lightning ground.
To safely dissipate lightning strokes into the earth.
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.
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.
At what distance from a ground electrode to remote earth is resistance of approximately 68
percent encountered?
One foot.
When would you not use a pure copper ground rod?
Mechanical strength of copper is inadequate.
For what reason should stainless steel ground rods not be used?
They are too expensive.
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.
Why is ground resistance more stable at a greater depth?
The soil is not affected as much by seasonal changes.
List four methods of obtaining better grounds.
(1) Deeper rod penetration.
(2) parallel ground rods.
(3) Soil replacement.
(4) Concrete encapsulation.
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.
What usually causes grounding problems?
They are due mostly to violations of article 250 of the NEC.
Where are you required to ground the neutral conductor?
The source side of the service entrance disconnect.
What term can be used when referring to the neutral conductor?
The neutral conductor may be referred to as the grounded conductor.
What term can be used when referring to the bare or green insulated conductor?
This conductor is also known as the grounding conductor.
Which two areas of grounding are you referring to when you use the term grounding?
System grounding and equipment grounding.
Define the term system ground.
It is a connection to ground from one of the conductors of an electric circuit, normally the neutral
conductor.
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.
With what type of distribution system (wye or delta) should you use a grounded neutral
connection?
Wye.
Where should you ground the neutral for electrical power sources?
At the transformer secondaries and at the generators.
How often should the primary common neutral be grounded throughout the circuit?
At intervals not to exceed 1/4 mile.
Should you connect the primary neutral conductor together with the secondary neutral conductor?
Yes, if the neutral conductor is effectively grounded.
What are you limiting when you ground the secondary side of a wye-connected transformer?
Transient overvoltages.
Should the equipment ground and the system ground be tied together?
Yes, normally the two are interconnected at some point.
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.