Electrical Flashcards
T/F: The grounded conductor and the grounding conductor are one and the same conductor and perform the same function.
False
Why are all the noncurrent-carrying metal parts bonded together in a wiring system?
A) to make the system sturdy
B) to stabilize the voltage
C) to provide a low-resistance path to ground
C) to provide a low-resistance path to ground
What NEC® article covers grounding and bonding?
Article 250
In a three-phase system, if Phase A conductor contacts Phase B conductor, is it a short circuit or a ground fault?
Short circuit
If a circuit breaker ahead of a fault trips at 100 amperes of current, what is the maximum value of fault current that may flow through a fault?
A) Cannot determine from this info
B) unlimited
C) 100A
100A
If a hot conductor contacts the metal enclosure of a panel, is this considered a ground fault or a short circuit?
ground fault
What do we have if the neutral conductor contacts a metal receptacle box? ground fault or short circuit
ground fault
T/F
System grounding connects the metal parts of the system, like the boxes and motor frame, to the electrical system’s neutral conductor.
False
Which one of the following systems does not have to be grounded?
A) 24V control circuit
B) 120V household circuit
C) 480V motor power
A) 24V control circuit
To be effective, grounding systems must _____.
A.
step down the voltage on the primary
B.
protect the system from lightning
C.
monitor the current
B. protect the system from lightning
Which of the following cannot be used as a grounding electrode?
A. Conductive water pipe B. Ring made of wire C. 10' black iron gas pipe
C. 10’ black iron gas pipe
Where would you find the requirements for sizing a grounding electrode conductor?
A. NEC Article 505 B. NEC Section 250.50 C. NEC Table 250.66
C. NEC Table 250.66
Which of the following materials cannot be used as a grounding electrode conductor?
A. Stranded galvanized steel B. Stranded aluminum C. Solid copper D. Stranded copper-clad aluminum
A. stranded galvanized steel
T/F: A metal underground tank or metal well casing can be used as a grounding electrode.
True
Equipment grounding connects to which of the following?
A. Enclosures B. Current-carrying conductors C. Neutral conductor
Enclosures
What is the EGC designed to carry? Question content area bottom Part 1 A. Line voltage B. Unbalanced current C. Fault current
c. fault current
What factor determines the size of the EGC? Question content area bottom Part 1 A. Number of duplex outlets in the circuit B. Size of the fuse in the circuit C. Ambient temperature D. Size of the "hot" conductor
size of the overcurrent protection
Which one of the following methods should not be used to ground a metal residential receptacle box?
Question content area bottom
Part 1
A.
A grounding screw secured to the box and designed for this purpose
B.
A grounding clip attached to the box
C.
Wrapping the bare ground around the screw that holds the receptacle
C
If multiple conduits enter an enclosure and the rules say that these conduits must be bonded, must you install a separate bonding jumper from each of them to the grounding terminals at the enclosure? Question content area bottom Part 1 A. No B. Yes, if more than three conduits C. Yes
No
The maximum length of the conductor allowed when running a bonding conductor outside a raceway is \_\_\_\_\_. Question content area bottom Part 1 A. 5 feet B. 10 feet C. 6 feet D. not specified in the NECSuperscript ®
6’
The purpose of an effective grounding path is to conduct any \_\_\_\_\_ that might occur in the system. Question content area bottom Part 1 A. fault current B. overcurrent C. unbalanced current
fault current
Which of the following circuits must be grounded? Question content area bottom Part 1 A. Secondary circuits in lighting systems B. Circuits for electrolytic cells C. Circuits for cranes that operate over combustible fibers. D. Separately derived systems
D. separately derived systems
Where must the EGC originate in a separately derived system that originates in a transformer? Question content area bottom Part 1 A. At the primary B. At the power company C. At the secondary
A. at the primary
When running power from one building to another, must you always run both the EGC and the grounded conductor to the second building? Question content area bottom Part 1 A. Only in certain conditions B. Never C. Yes
only in certain conditions
how long do rebars have to be to be used as ground
20’ long, and encased in concrete, and some other conditions
the metal frame of a building can be used as ground when buried at least how many ft
10’
Rod, pipe, and plate electrodes must have a resistance to ground of less than X ohms
25 ohms or less
A ground ring shall not use less than X gauge copper
2AWG
Grounding clamp connection must be made within how many feet from the point where the pipe enters the building
within 5’ of the pipe entering the building
grounding electrodes (ground rods) to be spaced at least X ft apart
at least 6’ apart
what materials can ground rods be made of…
stainless steel, iron, steel, copper plated
NOT aluminum
What table is used to size the grounding electrode conductor?
NEC Table 250.66
What table is used to determine the size of the service-entrance conductor? (determined from ampacity)
NEC Table 310.16
Table 310.16 shows that the service conductor size (copper wire at 75 degrees C) for a 150A service is 1/0 AWG. Which of the three AWG copper electrode conductor sizes below would be used with this service?
No 4
No 6
No 8
??
Which table is: Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment
NEC Table 250.122
Assuming 75 degree copper conductors, a 200A commercial service would require what size service conductor
1/0
2/0
3/0
4/0
3/0
Can a standard ohmmeter be used to effectively measure the resistance of a grounding system? Question content area bottom Part 1 Yes No
NO
Resistance to earth of a grounding electrode is commonly measured using the \_\_\_\_\_ method. Question content area bottom Part 1 A. zero sum B. potential difference C. fall-of-potential D. current-zeroing
fall of potential
Which of the following items is not a component of the resistance of a grounding system?
Question content area bottom
Part 1
A.
Resistance of the earth around the electrode
B.
Resistance of the conductor connecting the ground electrode
C.
Impedance of any transformers in the system
D.
Resistance between the ground electrode and the soil
C
Can a three-point resistance test be performed when only one electrode is installed? Question content area bottom Part 1 A. Yes, if the electrode is moved to three separate locations B. Yes C. No
NO
What is the LEAST height above areas accessible to vehicles that electric signs should be when NOT protected from physical damage? Question content area bottom Part 1 A. 16 feet B. 18 feet C. 14 feet D. 12 feet
C. 14’
What is the LEAST amount of free conductor, measured from the point in the box where it emerges from its raceway, that shall be left at each junction box or outlet box for splices or connection to devices? Question content area bottom Part 1 A. 6 inches B. 8 inches C. 12 inches D. 4 inches
6”
Unless the luminaire is identified as Type IC for insulation contact, thermal insulation should not be installed above a recessed luminaire or within how many inches of the recessed luminaire's enclosure? Question content area bottom Part 1 A. 3 inches B. 2 inches C. 1 inches D. 1/2 inch
3”
When connecting to luminaires, trade size 3/8 in. flexible metal conduit (FMC) is permitted to enclose tap conductors, provided the length of the FMC does NOT exceed \_\_\_\_\_. Question content area bottom Part 1 A. 4 feet B. 3 feet C. 8 feet D. 6 feet
D. 6’
Where a lighting track is installed with two (2), four (4) ft. sections, mounted end-to-end, how many supports are required? Question content area bottom Part 1 A. four B. two C. five D. three
D. 3
The EGC for a flexible metal conduit connection to a motor supplied with a 20A circuit is
A. 8 AWG copper
B. 10 AWG copper
C. 12 AWG copper
D. 14 AWG copper
check 250.122
c. 12AWG
Touch voltage extends to a distance of approximately \_\_\_\_\_ A. 1' B. 2' C. 3' D. 4'
??
Ground rod is called
Grounding electrode
Ground wire is called
Grounding electrode conductor
In regard to an isolated grounding type receptacle, the reason the insulated isolated grounding conductor is purposely NOT bonded to the outlet box is _____.
A. the reduction of electrical noise B. preventing the circuit breaker from tripping in the event of a ground-fault C. ensuring the circuit breaker will trip in the event of a ground-fault D. the reduction of voltage-drop
A.
the reduction of electrical noise
What is the LEAST depth of contact with the earth needed for a structural support member of a building or structure to be permitted to be used as a grounding electrode regardless of concrete encasing? Question content area bottom Part 1 A. 6 feet B. 10 feet C. 8 feet D. 20 feet
B.
10 feet
Where used outside of a building, aluminum or copper-clad aluminum grounding electrode conductors shall NOT be terminated WITHIN \_\_\_\_\_. Question content area bottom Part 1 A. 18 inches of the earth B. 3 feet of the earth C. 24 inches of the building D. 6 feet of the building
A.
18 inches of the earth
see 250.64(A)(3)
When two (2) ground rods are used to form the entire grounding electrode system of a building, the grounding conductor that bonds the two rods together shall NOT be required to be larger than size \_\_\_\_\_ copper, regardless of the size of the service-entrance conductors. Question content area bottom Part 1 A. 8 AWG B. 4 AWG C. 2 AWG D. 6 AWG
D.
6 AWG
see 250.66(A)
Bonding Jumpers are covered in NEC Table…..
Table 250.102(C)(1)
If you are bonding multiple disconnects, with a SEC of 1000 kcmil, the size of the bonding jumper is ___
2/0 copper
When an equipment bonding jumper is installed outside a raceway, the length is limited to not more than how many feet?
6’
The two types of grounding are __
system grounding and equipment grounding
Systems less than 50V are required to be grounded if the supply voltage to the transformer exceeds ___ to ground
150V
Circuits that cannot be grounded include certain circuits for cranes, electrolytic cells, secondary circuits on lighting systems, and isolated power systems in
healthcare facilities
Grounding methods include an underground water pipe in direct contact with the earth for more than ___
10’
The size of the GEC is based on the ___
service entrance conductor
The size of the EGC is based on the
breaker that feeds that circuit
The size of the bonding jumper on the supply side is based on the size of the ___ in each raceway
service conductors
The two main purposes of a neutral in a grounded system are to
- permit utilization of line-to-neutral voltage
2. create a low impedance return path for fault current to facilitate operation of the overcurrent device
Equipment grounding refers to connecting the normally non-current carrying metal parts of equipment to the system grounded conductor and/or ____
the grounding electrode conductor
which type of system is required to be grounded?
a. systems less than 50V supplied by grounded transformers
b. circuits for cranes that operate over combustible fibers in Class III locations
c. AC systems over 1kV that supply mobile or portable equipment?
d. circuits for electrolytic cells
c. ac systems over 1000V
A transformer-supplied system operating at less than 50V if the supply voltage to the transformer exceeds ___
150V to ground
A ground ring of 20’ of No 2 bare copper must be buried no less than ___
2.5’ below grade
To be effective, a grounding system must limit the voltage on the electrical system and protect it from ___
voltage surges
Service conductors are sized using Table…
310.16
The minimum length allowed for driven ground rods under normal conditions is ____
8’ minimum
The metallic noncurrent-carrying parts of an electrical system are bonded together to ensure ___
the proper operation of overcurrent devices in the event of a ground fault, and to prevent differences of potential btw different components
The size of the equipment grounding conductor is based on the
breaker
The main bonding jumper is sized based on the size of the _____.
a) service conductors
b) feeder conductors
c) largest motor load
d) largest overcurrent protective device
a) service conductors
The key to successfully clearing ground fault currents is _____.
a) maximizing impedance
b) electrical continuity
c) providing multiple electrical paths
d) utilizing threaded couplings
According to the NEC ® , the path to ground from circuits, equipment, and metal enclosures
must _____.
a) have sufficiently high impedance to facilitate the operation of protective devices
b) provide a permanent and continuous path sized to safely conduct potential fault current
c) rely on the earth as an effective ground fault current path
d) be capable of safely carrying twice the maximum current of the system
The bonding jumper for multiple disconnecting means is located _____.
a) between the feeder panel and the equipment
b) between the equipment and the equipment grounding bus
c) on the supply side of the service disconnect
d) between the equipment and the ground bar
A generator system that supplies power where the neutral is not connected to the utility
system, such as for carnivals, is known as a(n) _____.
a) separately derived system
b) autotransformer
c) utility secondary
d) premises-powered system
Which of the following is TRUE of the neutral in a grounded system?
a) It prohibits utilization of power at line-to-neutral voltage.
b) It prevents the current-carrying conductor from carrying an unbalanced load.
c) It provides a low-impedance return path for the flow of fault current to the source.
d) It supersedes the operation of overcurrent devices.
Which of the following is TRUE when installing grounding at more than one building?
a) The equipment grounding conductor is sized based on the overcurrent device protecting
the first building.
b) The grounded circuit conductor and the equipment grounding conductor must both be
extended to the second building.
c) Only the equipment grounding conductor is extended to the second building.
d) The second building never requires its own grounding electrode.
A transformer bonding jumper is routed with the feeder conductors from the transformer to
the equipment grounding bar in the panel and is known as a(n) _____.
a) grounding electrode conductor
b) supply-side bonding jumper
c) equipment grounding conductor
d) equipment bonding jumper
A ground tester can be used to measure the value of a grounding electrode’s _____.
a) voltage
b) current
c) resistance
d) capacitance
How many ungrounded conductors must be taken from the first structure to where the service
is located in the second structure when running 120V between buildings?
a) 1
b) 2
c) 3
d) 4
The fall-of-potential method is used to measure _____.
a) earth resistance
b) step voltage
c) induced currents
d) touch voltage
A ground test utilizing an auxiliary current electrode and an auxiliary potential electrode is known as the \_\_\_\_\_. a) one-point test b) three-point test c) five-point test d) seven-point test
When a new grounding system has been installed, it is advisable to conduct baseline three- point tests every \_\_\_\_\_. a) month for the first year b) season for the first year c) six months for the first year d) year
Worn motor bearings are most likely to result in a
a. temporary overload
b. sustained overload
c. short circuuit
d. ground fault
sustained overload
Where in the NEC do you find circuit breaker applications?
NEC 240.85
Define current rating vs interrupting capacity rating
ya do that
Every circuit breaker must have its interrupting rating shown on the breaker, unless rated for ___
5000A
When a common molded-case circuit breaker trips, in what position will the operating handle be?
halfway between on and off
What is the highest voltage rating for circuit breakers used on DC systems that UL recognizes?
600V
Where is the ampere rating located on the circuit breaker?
on the handle
What is normally the highest short circuit current in residential applications?
10,000A
When does the NEC allow you to use Edison-base fuses?
for replacements in existing installations
Overloads are often caused by _____.
a) wires crossing
b) motors starting
c) a wire touching a metal frame
d) a bare conductor contacting a metal tool
a wire touching a metal frame
Which of the following is TRUE regarding overload current?
a) Overload current is confined to normal conductive paths.
b) An overload is the same as a short circuit.
c) An overload is an unintended current path.
d) Protective devices must respond to all overloads.
protective devices must respond to all overloads
The requirements for overcurrent protection can be found in _____.
a) NEC Article 240
b) NEC Article 344
c) NEC Article 440
d) NEC Article 517
NEC article 240
Circuit breakers and fuses operate in a similar manner as a boiler’s _____.
a) expansion tank
b) pressure relief valve
c) heat exchanger
d) burner
pressure relief valve
Which of the following is TRUE with regard to circuit breakers?
a) The interrupting capacity is based on the system load.
b) The interrupting capacity is the same for each voltage level.
c) The interrupting capacity is based on its rated voltage.
d) The interrupting capacity is the same for each frequency.
b. the interrupting capacity is the same for each voltage level
The frame size of a 20A circuit breaker is _____.
a) 20A
b) 50A
c) 75A
d) 100A
100A
The interrupting rating of an FH-type circuit breaker is _____.
a) 5,000A
b) 10,000A
c) 30,000A
d) 65,000A
65000A
Circuits in which the breaker must be highly sensitive to amperage changes should use a(n) \_\_\_\_\_. a) non-automatic circuit breaker b) ambient-compensating circuit breaker c) standard magnetic breaker d) oil circuit breaker
?
A device that trips when a fault current to ground is 6mA or more is designated by UL as \_\_\_\_\_. a) Class A b) Class B c) Class H d) Class R
Class A
The heart is likely to stop when exposed to a current above _____.
a) 5mA
b) 30mA
c) 100mA
d) 200mA
200mA
Which of the following is TRUE regarding a dual-element fuse?
a) It is a single-use only device.
b) It cannot be used in circuits subject to temporary overloads.
c) It contains a fuse link connected in series with an overload element.
d) It should be oversized to prevent nuisance trips.
c. it contains a fuse link connected in series with an overload element
Type S fuses are available in sizes up to _____.
a) 30A
b) 60A
c) 100A
d) 225A
30A
Which of the following types of drawings helps when sizing fuses for a given application?
a) Single-line schematic
b) Large-scale detail
c) Building elevation drawing
d) Floor plan
a single line schematic
Cartridge fuses used for branch circuit protection must be marked with the ampere rating,
interrupting rating (if other than 10,000A), and the _____.
a) date manufactured
b) dimensions
c) expiration
d) voltage rating
voltage rating
The time-current relationship for a number of overcurrent devices connected in series is known as \_\_\_\_\_. a) switching b) looping c) stringing d) coordination
Coordination
Motor nameplates shall include the rated horsepower if ____ HP or more
1/8 HP (430.7)
The ____ branch circuit is that point from the last fuse or circuit breaker in the circuit out to the motor
motor
conductors supplying a single motor shall have an ampacity of ____ % the FLC rating as indicated on the appropriate FLC table
125%
The ___ is the device in a motor circuit which turns the motor ON or OFF
controller (430.2)
A ____ is an assembly of one or more sections with a common power bus and primarily containing motor control units
motor control center
