CALFORNIA C10 ELECTRICAL CORE EXAMS SET 2025/2026
QUESTIONS WITH ANSWERS RATED A+
✔✔How shall busbars be mounted in a panelboard?
A-Snug, but not tight.
B-Loose
C-Rigidly
D-Horizontal to the floor. - ✔✔The Correct Answer Is C
Insulated or bare busbars shall be rigidly mounted.
✔✔The maximum rating of overcurrent devices protecting panelboard instrument
circuits is _____.
A-10 amperes
B-20 amperes
C-15 amperes
D-30 amperes - ✔✔The Correct Answer Is C
Instrument circuits such as pilot lights and potential transformers shall be supplied by a
circuit that is protected by standard overcurrent devices rated 15 amperes or less. NEC
Section 408.32.
✔✔What is the minimum wire bending space allowed in a panelboard being fed with
paralleled pairs of 2/0 conductors entering the enclosure through the wall opposite the
terminals?
A-6 inches
B-7 inches
C-8 inches
D-9 inches - ✔✔The Correct Answer Is A
NEC Table 312.6(B)
✔✔What is the minium length required of a junction box in a straight pull?
A-Eight times the cross sectional area of the conductor.
B-Four times the cross sectional area of the largest conductor.
C-Eight times the trade diameter of the largest raceway.
D-Six times the trade diameter of the largest raceway. - ✔✔The Correct Answer Is C
In straight pulls, the length of the junction box must be at least eight times the diameter
of the largest raceway.
✔✔Knife switches rated over 1200 amperes at 250 volts or less, and at over 600
amperes at 251 to 600 volts, shall be opened only under what condition?
A-When switches are fully loaded.
B-When switches are isolated.
C-In case of fire.
D-Under no load. - ✔✔The Correct Answer Is D
Knife switches as specified in this question must not be opened under load. Therefore, if
a knife switch is providing a disconnecting means for a feeder serving, say, six motor
,controllers, each motor must be shut off before opening the knife switch, or else enough
motors must be shut off to obtain conditions below 1200 amperes at 250 volts or below
600 amperes at from 251 to 600 volts. NEC Section 404.13(A)
✔✔Panelboards must be mounted in _____.
A-cabinets
B-enclosures designed for the purpose
C-cutout boxes
D-Any of these. - ✔✔The Correct Answer Is D
NEC Section 408.18 allows panelboards to be enclosed in either cabinets, cutout
boxes, or enclosures designed for the purpose.
✔✔What type of front must be used for panelboard enclosures?
A-Live front
B-Dead front
C-Gray-colored front
D-Gray-colored front with yellow - ✔✔The Correct Answer Is B
NEC Section 408.18 requires all panelboard enclosures to be of the dead front type.
✔✔Metal panelboard cabinets and their related frames must be _____.
A-isolated from each other
B-separately bonded
C-in physical contact with each other
D-None of the above. - ✔✔The Correct Answer Is C
NEC Section 408.20 requires panelboard cabinets and their related frames, if of metal,
to be in physical contact with each other and grounded in accordance with NEC Article
250.
✔✔The working clearance between live parts for a system operating at 480 volts with
exposed live parts on one side and no live or grounded parts on the other side of the
working space must be a minimum of _____.
A-3 feet
B-3-1/2 feet
C-4 feet
D-5 feet - ✔✔The Correct Answer Is A
NEC Table 110.26(A) lists this situation as Condition 1 and calls for 3 feet working
clearance.
✔✔What size and type of continuous conductor is required for a bonding conductor
between equipment grounding terminal busses of normal and essential branch-circuit
panelboards in health care facilities?
A-No. 10 AWG insulated aluminum
B-No. 12 AWG insulated copper
C-No. 10 AWG insulated copper
D-No. 12 AWG insulated aluminum - ✔✔The Correct Answer Is C
, Such panelboards serving the same individual patient area must be bonded together
with an insulated continuous copper conductor not smaller than No.10 AWG.
✔✔What is the allowable ampacity for a 1/0 THHN conductor in a conduit with 5 other
current carrying conductors?
A-170 amps
B-150 amps
C-136 amps
D-200 amps - ✔✔The Correct Answer Is C
NEC Table 310.16 lists the ampacity for a 1/0 THHN conductor at 170 amps. However,
Article 310.15 requires conductors to be derated when more than 3 current carrying
conductors are in the same cable or raceway. A 1/0 THHN conductor at 80 percent
would be rated at 136 amperes.
✔✔The highest current rating of an Edison-base plug fuse is _____.
A-30 amperes
B-60 amperes
C-100 amperes
D-200 amperes - ✔✔The Correct Answer Is A
Plug fuses of the Edison-base type shall be classified at not over 125 volts and 30
amperes. NEC Section 240.51(A)
✔✔Edison-base plug fuses may be used only in _____.
A-new work
B-existing installations under specified conditions
C-motor control panels
D-motor circuits - ✔✔The Correct Answer Is B
Plug fuses of the Edison-base type shall be used only for replacements in existing
installations where there is no evidence of overfusing or tampering. NEC Section 240.51
✔✔When a circuit breaker trips, its operating handle will be in which of the following
positions?
A-Closed (energized) position.
B-Open position.
C-Half-way between the ON and OFF positions.
D-No change. - ✔✔The Correct Answer Is C
The conventional circuit-breaker handle has four possible positions: on, off, trip, and
reset. When tripped, the handle jumps to the middle position.
✔✔Plug fuses of 15 ampere and lower rating must be identified by what type of window
configuration?
A-Round
B-Hexagonal
C-Square
D-Octagonal - ✔✔The Correct Answer Is B
QUESTIONS WITH ANSWERS RATED A+
✔✔How shall busbars be mounted in a panelboard?
A-Snug, but not tight.
B-Loose
C-Rigidly
D-Horizontal to the floor. - ✔✔The Correct Answer Is C
Insulated or bare busbars shall be rigidly mounted.
✔✔The maximum rating of overcurrent devices protecting panelboard instrument
circuits is _____.
A-10 amperes
B-20 amperes
C-15 amperes
D-30 amperes - ✔✔The Correct Answer Is C
Instrument circuits such as pilot lights and potential transformers shall be supplied by a
circuit that is protected by standard overcurrent devices rated 15 amperes or less. NEC
Section 408.32.
✔✔What is the minimum wire bending space allowed in a panelboard being fed with
paralleled pairs of 2/0 conductors entering the enclosure through the wall opposite the
terminals?
A-6 inches
B-7 inches
C-8 inches
D-9 inches - ✔✔The Correct Answer Is A
NEC Table 312.6(B)
✔✔What is the minium length required of a junction box in a straight pull?
A-Eight times the cross sectional area of the conductor.
B-Four times the cross sectional area of the largest conductor.
C-Eight times the trade diameter of the largest raceway.
D-Six times the trade diameter of the largest raceway. - ✔✔The Correct Answer Is C
In straight pulls, the length of the junction box must be at least eight times the diameter
of the largest raceway.
✔✔Knife switches rated over 1200 amperes at 250 volts or less, and at over 600
amperes at 251 to 600 volts, shall be opened only under what condition?
A-When switches are fully loaded.
B-When switches are isolated.
C-In case of fire.
D-Under no load. - ✔✔The Correct Answer Is D
Knife switches as specified in this question must not be opened under load. Therefore, if
a knife switch is providing a disconnecting means for a feeder serving, say, six motor
,controllers, each motor must be shut off before opening the knife switch, or else enough
motors must be shut off to obtain conditions below 1200 amperes at 250 volts or below
600 amperes at from 251 to 600 volts. NEC Section 404.13(A)
✔✔Panelboards must be mounted in _____.
A-cabinets
B-enclosures designed for the purpose
C-cutout boxes
D-Any of these. - ✔✔The Correct Answer Is D
NEC Section 408.18 allows panelboards to be enclosed in either cabinets, cutout
boxes, or enclosures designed for the purpose.
✔✔What type of front must be used for panelboard enclosures?
A-Live front
B-Dead front
C-Gray-colored front
D-Gray-colored front with yellow - ✔✔The Correct Answer Is B
NEC Section 408.18 requires all panelboard enclosures to be of the dead front type.
✔✔Metal panelboard cabinets and their related frames must be _____.
A-isolated from each other
B-separately bonded
C-in physical contact with each other
D-None of the above. - ✔✔The Correct Answer Is C
NEC Section 408.20 requires panelboard cabinets and their related frames, if of metal,
to be in physical contact with each other and grounded in accordance with NEC Article
250.
✔✔The working clearance between live parts for a system operating at 480 volts with
exposed live parts on one side and no live or grounded parts on the other side of the
working space must be a minimum of _____.
A-3 feet
B-3-1/2 feet
C-4 feet
D-5 feet - ✔✔The Correct Answer Is A
NEC Table 110.26(A) lists this situation as Condition 1 and calls for 3 feet working
clearance.
✔✔What size and type of continuous conductor is required for a bonding conductor
between equipment grounding terminal busses of normal and essential branch-circuit
panelboards in health care facilities?
A-No. 10 AWG insulated aluminum
B-No. 12 AWG insulated copper
C-No. 10 AWG insulated copper
D-No. 12 AWG insulated aluminum - ✔✔The Correct Answer Is C
, Such panelboards serving the same individual patient area must be bonded together
with an insulated continuous copper conductor not smaller than No.10 AWG.
✔✔What is the allowable ampacity for a 1/0 THHN conductor in a conduit with 5 other
current carrying conductors?
A-170 amps
B-150 amps
C-136 amps
D-200 amps - ✔✔The Correct Answer Is C
NEC Table 310.16 lists the ampacity for a 1/0 THHN conductor at 170 amps. However,
Article 310.15 requires conductors to be derated when more than 3 current carrying
conductors are in the same cable or raceway. A 1/0 THHN conductor at 80 percent
would be rated at 136 amperes.
✔✔The highest current rating of an Edison-base plug fuse is _____.
A-30 amperes
B-60 amperes
C-100 amperes
D-200 amperes - ✔✔The Correct Answer Is A
Plug fuses of the Edison-base type shall be classified at not over 125 volts and 30
amperes. NEC Section 240.51(A)
✔✔Edison-base plug fuses may be used only in _____.
A-new work
B-existing installations under specified conditions
C-motor control panels
D-motor circuits - ✔✔The Correct Answer Is B
Plug fuses of the Edison-base type shall be used only for replacements in existing
installations where there is no evidence of overfusing or tampering. NEC Section 240.51
✔✔When a circuit breaker trips, its operating handle will be in which of the following
positions?
A-Closed (energized) position.
B-Open position.
C-Half-way between the ON and OFF positions.
D-No change. - ✔✔The Correct Answer Is C
The conventional circuit-breaker handle has four possible positions: on, off, trip, and
reset. When tripped, the handle jumps to the middle position.
✔✔Plug fuses of 15 ampere and lower rating must be identified by what type of window
configuration?
A-Round
B-Hexagonal
C-Square
D-Octagonal - ✔✔The Correct Answer Is B
