CSLB Trade — Electrical (C-10) — All Questions

Bends in electrical metallic tubing (EMT) must be made so that which of the following is true?

• a.The radius is as tight as possible
• b.The tubing is heated first
• c.At least six bends are used
• d.The tubing is not damaged and its internal diameter is not effectively reduced✓

Section 358.24 requires EMT bends to be made so the tubing is not damaged and the internal diameter is not effectively reduced, using at least the radius shown in Chapter 9, Table 2. Kinking or flattening the tubing violates this. Heating EMT, forcing the tightest radius, or a fixed number of bends are not the standard.2023 NEC §358.24

Direct-buried conductors or cables emerging from grade must be protected by enclosures or raceways from the required cover depth up to what height above finished grade?

• a.5 ft
• b.6 ft
• c.8 ft✓
• d.3 ft

Section 300.5(D)(1) requires direct-buried conductors and cables emerging from grade to be protected by enclosures or raceways from the required burial depth to at least 8 ft above finished grade. Lower heights of 3, 5, and 6 ft leave the emerging conductors exposed to physical damage.2023 NEC §300.5(D)(1)

Rigid polyvinyl chloride conduit (PVC) is permitted to be used in which of the following locations?

• a.Only where exposed to sunlight
• b.Only inside metal enclosures
• c.Only in dry indoor locations
• d.Wet locations and direct burial where listed✓

Section 352.10 permits rigid PVC conduit in wet locations, corrosive environments, concealed work, and direct burial where properly listed and assembled. Restricting it to dry indoor use, sunlight-only, or inside metal enclosures misstates its permitted uses. PVC is widely used underground for branch-circuit feeders.2023 NEC §352.10

Electrical metallic tubing (EMT) is generally not permitted to be used in which condition?

• a.Concealed in walls
• b.Exposed on masonry
• c.Where subject to severe physical damage✓
• d.In dry indoor locations

Section 358.12 prohibits EMT where subject to severe physical damage. EMT is permitted concealed in walls, in dry locations, and exposed on masonry when properly supported and protected. Only the severe-physical-damage condition is a listed prohibition among these choices.2023 NEC §358.12

Liquidtight flexible metal conduit (LFMC) is especially suited for which of the following uses?

• a.Connections to equipment where flexibility and protection from liquids are needed✓
• b.As a general lighting raceway in dry ceilings only
• c.Only for direct burial without fittings
• d.Only for service-entrance conductors

Section 350.10 permits LFMC where flexibility or protection from liquids, vapors, or solids is required, such as connections to motors and outdoor equipment. It is not limited to dry ceilings, is not intended specifically for service-entrance conductors, and requires listed fittings rather than bare direct burial.2023 NEC §350.10

Rigid metal conduit (RMC) is permitted to be used under which of the following conditions?

• a.In all atmospheric conditions and occupancies✓
• b.Only in dwellings
• c.Only where concealed
• d.Only in dry locations

Section 344.10 permits RMC in all atmospheric conditions and occupancies, with appropriate corrosion protection where needed. It is one of the most robust raceways. Limiting it to dry, concealed, or dwelling-only uses understates the broad permission the code grants RMC.2023 NEC §344.10

Cables or raceways installed under metal-corrugated sheet roof decking must be kept at least what distance from the lowest surface of the roof decking to the top of the raceway or cable?

• a.2 in
• b.1 in
• c.3/4 in
• d.1-1/2 in✓

Section 300.4(E) requires cables and raceways under metal-corrugated sheet roof decking to be kept at least 1-1/2 in from the lowest surface of the decking, protecting the wiring from roofing screws. The smaller 3/4-in and 1-in distances are insufficient, and 2 in is more than the code minimum.2023 NEC §300.4(E)

What is the minimum working-space depth for electrical equipment operating at 151 to 600 volts to ground under Condition 2 (exposed live parts on one side and grounded parts on the other)?

• a.3.5 ft✓
• b.4 ft
• c.3 ft
• d.2.5 ft

Table 110.26(A)(1) requires 3.5 ft of working clearance for 151-600 V to ground under Condition 2. Condition 1 at that voltage is 3 ft and Condition 3 is 4 ft. 2.5 ft is below any required minimum in this range.2023 NEC §110.26(A)(1)

In a commercial (other than dwelling) building, a 125-volt, 20-ampere receptacle installed in a bathroom must have what protection?

• a.Surge only
• b.AFCI only
• c.No protection
• d.GFCI✓

Section 210.8(B) requires GFCI protection for 125-V through 250-V receptacles in non-dwelling bathrooms, kitchens, rooftops, and similar locations. AFCI is not the specified requirement here; 'no protection' and surge-only leave the shock hazard unaddressed.2023 NEC §210.8(B)

Under 240.4(D), what is the maximum overcurrent protection permitted for a 14 AWG copper branch-circuit conductor, absent a specific exception?

• a.15 A✓
• b.25 A
• c.30 A
• d.20 A

Section 240.4(D)(3) limits 14 AWG copper conductors to a maximum overcurrent device of 15 A. This is why 14 AWG is used on 15-A branch circuits. 20, 25, and 30 A all exceed the small-conductor protection limit for 14 AWG copper.2023 NEC §240.4(D)

Under 240.4(D), what is the maximum overcurrent protection permitted for a 12 AWG copper branch-circuit conductor, absent a specific exception?

• a.30 A
• b.20 A✓
• c.25 A
• d.40 A

Section 240.4(D)(5) limits 12 AWG copper conductors to a maximum overcurrent device of 20 A, which is why 12 AWG is standard for 20-A branch circuits. 25, 30, and 40 A all exceed the small-conductor protection limit for 12 AWG copper.2023 NEC §240.4(D)

The rating of a branch circuit supplying two or more outlets is determined by what?

• a.The largest conductor
• b.The voltage only
• c.The ampere rating of the overcurrent device protecting the circuit✓
• d.The receptacle count

Section 210.3 states that a branch circuit's rating is determined by the maximum permitted ampere rating of the overcurrent device protecting the circuit, using standard sizes such as 15, 20, 30, 40, and 50 A. The conductor size, number of receptacles, or voltage alone do not define the branch-circuit rating.2023 NEC §210.18

The working space required in front of electrical equipment must be kept clear and, in general, may be used for what purpose?

• a.No storage; it must remain clear for access✓
• b.Temporary parts staging
• c.Storage of conduit
• d.Mounting a subpanel

Section 110.26(B) requires the working space to be kept clear and prohibits using it for storage; when energized equipment needs servicing, the space must be clear. Using it for conduit storage, parts staging, or mounting another panel would obstruct required access to live parts.2023 NEC §110.26(B)

Couplings and connectors used with electrical metallic tubing (EMT) in a wet location must be what?

• a.Painted
• b.Set-screw type
• c.Listed for use in wet locations✓
• d.Threaded

Section 358.42 requires EMT couplings and connectors used in wet locations to be listed for wet locations, commonly the raintight compression type. Plain set-screw fittings are not raintight, threading does not apply to EMT couplings, and paint does not make a fitting suitable for wet locations.2023 NEC §358.42

An outlet box used as the sole support for a ceiling-suspended (paddle) fan must be what?

• a.A handy box
• b.Any 4-inch square box
• c.Listed and marked for that purpose✓
• d.A plastic device box

Section 314.27(C) requires an outlet box used as the sole support of a ceiling-suspended paddle fan to be listed and marked for that application, and to support the fan weight. A standard 4-in square box, a plastic device box, or a handy box not so listed cannot serve as the sole fan support.2023 NEC §314.27(C)

A 4" x 1-1/2" square box has a volume of 21.0 in³. With no clamps, devices, or other allowances, what is the maximum number of 14 AWG conductors permitted in the box?

• a.8
• b.11
• c.10✓
• d.9

Each 14 AWG conductor requires a 2.00 in³ volume allowance from Table 314.16(B). 21.0 ÷ 2.00 = 10.5, and you round down to 10 conductors. Rounding up to 11 would exceed the box volume, and 9 or 8 understates the count.2023 NEC §314.16(B)

Using the same 21.0 in³ box with no other fill allowances, what is the maximum number of 12 AWG conductors permitted?

• a.9✓
• b.10
• c.7
• d.8

Each 12 AWG conductor requires 2.25 in³ per Table 314.16(B). 21.0 ÷ 2.25 = 9.33, rounded down to 9 conductors. 10 would exceed the volume, and 8 or 7 undercounts.2023 NEC §314.16(B)

Per Table 314.16(B), what is the free-space volume allowance required for a single 12 AWG conductor?

• a.2.00 in³
• b.3.00 in³
• c.2.50 in³
• d.2.25 in³✓

Table 314.16(B) assigns 2.25 in³ per 12 AWG conductor. 2.00 in³ is the value for 14 AWG, 2.50 in³ is for 10 AWG, and 3.00 in³ is for 8 AWG.2023 NEC §314.16(B)

In a box-fill calculation, a single device (a receptacle or switch mounted on a yoke or strap) counts as how many conductor volume allowances?

• a.3
• b.1
• c.2✓
• d.0

Per 314.16(B)(4), each yoke or strap containing one or more devices counts as two volume allowances, based on the largest conductor connected to the device. Counting it as 1 or 0 understates the fill; a standard single device is not 3.2023 NEC §314.16(B)(4)

A box contains three internal cable clamps. In the box-fill calculation, how many volume allowances do the clamps require in total?

• a.0 (clamps are exempt)
• b.3 (one per clamp)
• c.1 (a single allowance)✓
• d.6 (two per clamp)

Per 314.16(B)(2), where one or more internal clamps are present, a single volume allowance is required based on the largest conductor in the box — not one per clamp. So three clamps still count as only one allowance.2023 NEC §314.16(B)(2)

A box has four 12 AWG equipment grounding conductors entering it. How are they counted in the box-fill calculation?

• a.Each counts individually (four allowances)
• b.They are never counted
• c.They count as two allowances
• d.All together count as a single volume allowance✓

Per 314.16(B)(5), all equipment grounding conductors together count as a single volume allowance, based on the largest EGC present. Counting them individually overstates the fill, and they are not exempt from the calculation.2023 NEC §314.16(B)(5)

A box contains five 12 AWG current-carrying conductors, one 12 AWG equipment grounding conductor, one internal cable clamp, and one switch on a yoke (all conductors 12 AWG). What total box volume is required?

• a.22.50 in³
• b.18.00 in³
• c.20.25 in³✓
• d.15.75 in³

At 2.25 in³ each: five conductors = 11.25, EGCs (as one) = 2.25, clamp (as one) = 2.25, and the yoke = 2 × 2.25 = 4.50. Total = 11.25 + 2.25 + 2.25 + 4.50 = 20.25 in³. The other values omit one or more required allowances.2023 NEC §314.16(B)

A single unbroken conductor passes straight through a box without being spliced or terminated. For box fill, it is counted as how many conductors?

• a.One-half
• b.One✓
• c.Two
• d.Zero

Per 314.16(B)(1), each conductor that runs through the box without splice or termination is counted once. It is not exempt (zero) and not doubled; a conductor is only counted twice when it is looped unbroken with a length of at least twice the minimum required for free conductors.2023 NEC §314.16(B)(1)

How are conductors that both originate and terminate within the box (such as short pigtails or jumpers) treated in a box-fill calculation?

• a.They are not counted✓
• b.They count as clamp allowances
• c.They count as one each
• d.They count as two each

Per 314.16(B)(1), a conductor that originates and terminates within the box, such as a pigtail, is not counted in the box fill. Only conductors that enter and are not spliced (or that terminate on a device) get an allowance.2023 NEC §314.16(B)(1)

Per Chapter 9, Table 1, what is the maximum permitted conduit fill percentage when three or more conductors are installed in a raceway?

• a.60%
• b.53%
• c.31%
• d.40%✓

Chapter 9, Table 1 limits fill to 40% for three or more conductors. 53% is the limit for a single conductor, 31% is for exactly two conductors, and 60% is not a code fill value.2023 NEC Chapter 9, Table 1

Per Chapter 9, Table 1, what is the maximum permitted fill percentage when exactly two conductors are installed in a conduit?

• a.31%✓
• b.25%
• c.53%
• d.40%

Table 1 sets a 31% fill limit for exactly two conductors, reflecting the jamming ratio concern. 40% applies to three or more, 53% to a single conductor, and 25% is not used.2023 NEC Chapter 9, Table 1

Per Chapter 9, Table 1, what is the maximum permitted fill percentage when only one conductor is installed in a conduit?

• a.31%
• b.60%
• c.53%✓
• d.40%

A single conductor may fill up to 53% of the conduit's internal area per Table 1. 31% is for two conductors, 40% for three or more, and 60% is not a code value.2023 NEC Chapter 9, Table 1

Per Annex C, Table C.1, what is the maximum number of 12 AWG THHN conductors permitted in 1/2" EMT?

• a.7
• b.12
• c.9✓
• d.5

Table C.1 lists 9 for 12 AWG THHN in 1/2" EMT. 12 is the count for 14 AWG, 5 is for 10 AWG, and 7 is not a listed value.2023 NEC Annex C, Table C.1

Per Annex C, Table C.1, what is the maximum number of 14 AWG THHN conductors permitted in 1/2" EMT?

• a.12✓
• b.15
• c.9
• d.10

Table C.1 lists 12 for 14 AWG THHN in 1/2" EMT. 9 is the count for 12 AWG, and 10 or 15 are not listed values for this size.2023 NEC Annex C, Table C.1

Per Annex C, Table C.1, what is the maximum number of 12 AWG THHN conductors permitted in 3/4" EMT?

• a.16✓
• b.9
• c.12
• d.22

Table C.1 lists 16 for 12 AWG THHN in 3/4" EMT. 22 is the count for 14 AWG in 3/4" EMT, and 9 is the count for 12 AWG in the smaller 1/2" EMT.2023 NEC Annex C, Table C.1

Per Annex C, Table C.1, what is the maximum number of 10 AWG THHN conductors permitted in 1/2" EMT?

• a.9
• b.7
• c.5✓
• d.3

Table C.1 lists 5 for 10 AWG THHN in 1/2" EMT. 9 is the value for 12 AWG, 3 is the value for 8 AWG, and 7 is not listed for this size.2023 NEC Annex C, Table C.1

The internal cross-sectional area of 1/2" EMT is 0.304 in³ per Table 4. For three or more conductors, what usable fill area (40%) is available?

• a.0.161 in²
• b.0.122 in²✓
• c.0.094 in²
• d.0.304 in²

0.304 × 0.40 = 0.122 in². The 31% (two-conductor) area would be 0.094 in² and the 53% (single-conductor) area would be 0.161 in²; 0.304 is the full 100% area.2023 NEC Chapter 9, Table 4

The internal area of 3/4" EMT is 0.533 in² per Table 4. What is the 40% usable fill area for three or more conductors?

• a.0.213 in²✓
• b.0.165 in²
• c.0.283 in²
• d.0.122 in²

0.533 × 0.40 = 0.213 in². The 31% area is 0.165 in² and the 53% area is 0.283 in²; 0.122 in² is the 40% area of the smaller 1/2" EMT.2023 NEC Chapter 9, Table 4

Given a 40% usable fill area of 0.213 in² (3/4" EMT) and a 12 AWG THHN cross-sectional area of 0.0133 in² (Table 5), how many 12 AWG THHN conductors fit?

• a.22
• b.16✓
• c.9
• d.12

0.213 ÷ 0.0133 = 16.0, so 16 conductors fit — matching Annex C. 9 corresponds to 1/2" EMT, 22 is the 14 AWG count for 3/4", and 12 is not correct here.2023 NEC Chapter 9, Table 4

Six current-carrying 12 AWG THHN conductors (90°C, 30 A base) share a raceway. Applying only the adjustment factor for 4–6 conductors, what is the adjusted ampacity?

• a.21 A
• b.30 A
• c.24 A✓
• d.27 A

The adjustment factor for 4–6 current-carrying conductors is 80%. 30 A × 0.80 = 24 A. 70% (21 A) applies to 7–9 conductors, and 30 A ignores the required adjustment.2023 NEC §310.15(C)(1)

Per Table 310.15(C)(1), what adjustment (derating) factor applies when there are 7 to 9 current-carrying conductors in a raceway?

• a.80%
• b.70%✓
• c.50%
• d.60%

The table assigns 70% for 7–9 current-carrying conductors. 80% is for 4–6, 50% is for 10–20, and 60% is not a listed factor.2023 NEC §310.15(C)(1)

Per Table 310.15(C)(1), what adjustment factor applies when there are 4 to 6 current-carrying conductors in a raceway?

• a.60%
• b.50%
• c.70%
• d.80%✓

The table assigns 80% for 4–6 current-carrying conductors. 70% is for 7–9, 50% is for 10–20, and 60% is not a listed factor.2023 NEC §310.15(C)(1)

Per Table 310.15(C)(1), what adjustment factor applies when there are 10 to 20 current-carrying conductors in a raceway?

• a.45%
• b.80%
• c.50%✓
• d.70%

The table assigns 50% for 10–20 current-carrying conductors. 80% is for 4–6, 70% is for 7–9, and 45% is for 21–30 conductors.2023 NEC §310.15(C)(1)

In a 3-wire, single-phase circuit (two hots and a neutral), how is the neutral treated when counting current-carrying conductors for adjustment?

• a.Counted as one-half a conductor
• b.Counted only if it is 12 AWG
• c.Not counted, since it carries only unbalanced current✓
• d.Always counted as current-carrying

Per 310.15(E), the neutral of a 3-wire single-phase circuit carries only the unbalanced current and is not counted as a current-carrying conductor. It would be counted only in a 4-wire wye supplying significant nonlinear (harmonic) load.2023 NEC §310.15(E)

In a 4-wire, 3-phase wye circuit supplying nonlinear (harmonic-producing) loads, how is the neutral treated for conductor-count adjustment?

• a.It is counted as one-half
• b.It counts only if it is bare
• c.It is counted as a current-carrying conductor✓
• d.It is never counted

Per 310.15(E), where the major portion of the load is nonlinear, harmonic currents load the neutral, so it must be counted as a current-carrying conductor. This differs from a balanced wye neutral, which normally is not counted.2023 NEC §310.15(E)

Is an equipment grounding conductor (EGC) ever counted as a current-carrying conductor when applying conductor-count adjustment factors?

• a.Only when it is 12 AWG
• b.No, it is never counted✓
• c.Only when it is bare
• d.Yes, always

Per 310.15(E), a grounding or bonding conductor is not counted as a current-carrying conductor because it carries current only under fault conditions. Its size and whether it is bare do not change this.2023 NEC §310.15(E)

An 8 AWG THHN copper conductor (55 A at the 90°C column) is installed where the ambient temperature is 46–50°C. Using the 90°C correction factor of 0.82, what is the corrected ampacity?

• a.50 A
• b.41 A
• c.55 A
• d.45 A✓

55 A × 0.82 = 45.1 A, rounded to 45 A. Using no correction (55 A) ignores the elevated ambient, and the other values apply the wrong factor.2023 NEC §310.15(B)

Six current-carrying 10 AWG THHN copper conductors (40 A at 90°C) run in a raceway at 40°C ambient. Applying the 0.91 ambient correction and the 0.80 conductor-count adjustment, what is the resulting ampacity?

• a.29 A✓
• b.35 A
• c.40 A
• d.32 A

40 A × 0.91 × 0.80 = 29.1 A, or about 29 A. Both factors must be applied from the 90°C base; using only one factor overstates the result.2023 NEC §310.15

For a branch circuit rated 100 A or less, which temperature column must be used for conductor ampacity at the terminations unless the equipment or terminals are listed for a higher temperature?

• a.Any column may be used
• b.90°C
• c.60°C✓
• d.75°C

Per 110.14(C)(1), for circuits 100 A or less the 60°C column applies unless the equipment/terminals are listed for 75°C (or higher). The 90°C column is never the termination limit, and you cannot freely choose the column.2023 NEC §110.14(C)

A 90°C-rated conductor is terminated on equipment whose lugs are listed for 75°C. Which temperature column limits the conductor's final ampacity at that termination?

• a.55°C
• b.60°C
• c.75°C✓
• d.90°C

Per 110.14(C), the final ampacity cannot exceed the lowest-rated termination — here 75°C. The 90°C rating may be used only for derating math, and 60°C would apply only if the terminals were rated for 60°C.2023 NEC §110.14(C)

Under what circumstance may the 90°C ampacity column of Table 310.16 be used?

• a.Only for applying adjustment and correction (derating) factors✓
• b.It may never be used
• c.For the branch-circuit load calculation
• d.For final conductor sizing at the terminals

The 90°C column serves only as the starting point for adjustment and correction factors, provided the conductor is 90°C rated. The final ampacity is still limited by the termination temperature per 110.14(C), so it cannot set the final size directly.2023 NEC §110.14(C)

Per Table 310.16, what is the ampacity of an 8 AWG copper THHN conductor in the 90°C column?

• a.50 A
• b.55 A✓
• c.40 A
• d.45 A

Table 310.16 lists 55 A for 8 AWG copper at 90°C. 40 A is the 60°C value and 50 A is the 75°C value for 8 AWG copper; 45 A is not a listed value for this size.2023 NEC §310.16

Per Table 310.16, what is the ampacity of a 12 AWG copper conductor in the 75°C column (before any small-conductor overcurrent limit)?

• a.20 A
• b.25 A✓
• c.35 A
• d.30 A

Table 310.16 lists 25 A for 12 AWG copper at 75°C. 20 A is the 60°C value (and also the 240.4(D) OCPD limit), while 30 A is the 90°C value; 35 A is for 10 AWG.2023 NEC §310.16

Per Table 310.16, what is the ampacity of a 10 AWG copper conductor in the 60°C column?

• a.40 A
• b.35 A
• c.25 A
• d.30 A✓

Table 310.16 lists 30 A for 10 AWG copper at 60°C. 35 A is the 75°C value and 40 A is the 90°C value for 10 AWG copper; 25 A is the 12 AWG (75°C) value.2023 NEC §310.16

Per Table 310.16, what is the ampacity of a 6 AWG copper conductor in the 75°C column?

• a.65 A✓
• b.85 A
• c.75 A
• d.55 A

Table 310.16 lists 65 A for 6 AWG copper at 75°C. 55 A is the 60°C value and 75 A is the 90°C value for 6 AWG copper; 85 A is the 75°C value for 4 AWG.2023 NEC §310.16