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

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

Per 334.80, the ampacity of Type NM (nonmetallic-sheathed) cable is based on which temperature column of Table 310.16?

• a.Any column, at the installer's choice
• b.90°C
• c.60°C✓
• d.75°C

Section 334.80 requires NM cable ampacity to be taken from the 60°C column, even though the conductors themselves are 90°C rated. The 90°C rating may be used only for derating calculations, not as the base ampacity.2023 NEC §334.80

For Type NM cable, the 90°C rating of its conductors may be used for what purpose?

• a.Only for adjustment and correction (derating) calculations✓
• b.It may not be used at all
• c.For establishing the final ampacity
• d.For the load calculation

Per 334.80, the 90°C column may be used as the starting point when applying ambient and conductor-count factors, but the final NM ampacity is still governed by the 60°C column. It cannot set the final ampacity directly.2023 NEC §334.80

A 12-2 Type NM cable (two 12 AWG conductors plus ground) is used for a general branch circuit. Using the required NM temperature column, what is the ampacity of its 12 AWG conductors?

• a.20 A✓
• b.25 A
• c.15 A
• d.30 A

NM ampacity uses the 60°C column, where 12 AWG copper is 20 A. 25 A is the 75°C value and 30 A is the 90°C value, neither of which applies as the base for NM; 15 A is the 14 AWG (60°C) value.2023 NEC §334.80

Per 334.30, Type NM cable must be secured and supported at intervals not exceeding what distance along the run?

• a.4-1/2 ft (1.4 m)✓
• b.6 ft (1.8 m)
• c.3 ft (900 mm)
• d.10 ft (3.0 m)

Section 334.30 requires NM cable to be secured at intervals not exceeding 4-1/2 ft, and within 12 in of every box or fitting. 6 ft is the MC interval, while 3 ft and 10 ft are not NM support values.2023 NEC §334.30

Per 334.12, which of the following installations is NOT permitted for Type NM cable?

• a.Embedded in poured concrete✓
• b.Dry interior stud wall of a dwelling
• c.Concealed in a dry attic
• d.Exposed in a dry, protected location

Section 334.12 prohibits NM cable from being embedded in poured concrete, aggregate, or plaster, and from wet or damp locations. Dry interior walls, dry attics, and protected exposed dry runs are all permitted uses under 334.10.2023 NEC §334.12

Per 330.30, Type MC cable must be supported and secured at intervals not exceeding what distance?

• a.4-1/2 ft (1.4 m)
• b.3 ft (900 mm)
• c.6 ft (1.8 m)✓
• d.10 ft (3.0 m)

Section 330.30 requires MC cable to be secured at intervals not exceeding 6 ft, and within 12 in of a box where practicable. 4-1/2 ft is the NM/AC interval; 3 ft and 10 ft are not MC support values.2023 NEC §330.30

Which statement about Type MC cable ampacity is correct?

• a.MC is always taken at the 90°C column regardless of terminations
• b.MC ampacity may be based on the 75°C or 90°C rating of its conductors, subject to terminations✓
• c.MC is always limited to the 75°C column
• d.Like NM, MC ampacity is limited to the 60°C column

Per 330.80, MC cable ampacity follows 310.15 based on the conductor temperature rating (commonly 90°C for derating), then limited by the termination temperature per 110.14(C). Unlike NM, it is not capped at 60°C, but it is also not simply taken at 90°C at the terminals.2023 NEC §330.80

Under what condition may Type MC cable be installed in a wet location?

• a.Only when it is listed and identified for wet locations with a suitable moisture-impervious jacket✓
• b.Only where installed underground
• c.Never, MC is dry-location only
• d.Always, MC is unrestricted

Per 330.10, MC cable may be used in wet locations only where the metallic covering is impervious to moisture (or a jacket is provided) and the cable is listed/identified for the use. It is not unrestricted, and wet-location use is not limited to underground runs.2023 NEC §330.10

Per 320.40, what must be installed at each termination of Type AC (armored) cable to protect the conductors from the cut edge of the metal armor?

• a.An anti-short insulating bushing ("red head")✓
• b.A grounding bushing
• c.A cable connector only
• d.A locknut

Section 320.40 requires an insulating anti-short bushing, commonly called a red head, at each armored-cable termination to protect the conductor insulation from the sharp armor. A locknut or connector alone does not protect against the cut armor edge, and a grounding bushing serves a different purpose.2023 NEC §320.40

Per 320.30, Type AC cable must be secured and supported at intervals not exceeding what distance?

• a.3 ft (900 mm)
• b.6 ft (1.8 m)
• c.4-1/2 ft (1.4 m)✓
• d.10 ft (3.0 m)

Section 320.30 requires AC cable to be secured at intervals not exceeding 4-1/2 ft, and within 12 in of every box or fitting. 6 ft is the MC interval; 3 ft and 10 ft are not AC support values.2023 NEC §320.30

Which cable relies on its metal armor together with an internal aluminum bonding strip to serve as the equipment grounding path?

• a.Type NM
• b.Type MC
• c.Type AC✓
• d.Type UF

Per 320.100, Type AC cable includes an internal bonding strip that, combined with the armor, forms an effective ground-fault return path. Type MC generally includes a separate equipment grounding conductor, while NM and UF use an insulated or bare EGC, not the armor.2023 NEC §320.100

The NEC informational note recommends that voltage drop on a branch circuit not exceed what percentage of the circuit voltage?

• a.3%✓
• b.2%
• c.5%
• d.10%

The informational note to 210.19(A) recommends a maximum 3% voltage drop on a branch circuit for reasonable efficiency. 5% is the combined feeder-plus-branch recommendation, and 2% or 10% are not the branch-circuit figure.2023 NEC §210.19(A), Informational Note

For the combined feeder plus branch circuit, the NEC informational note recommends total voltage drop not exceed what percentage?

• a.5%✓
• b.2%
• c.8%
• d.3%

The informational notes recommend not more than 3% on the feeder and not more than 5% combined for feeder plus branch. 3% alone is the branch-circuit figure, and 2% or 8% are not the recommended totals.2023 NEC §215.2(A)(1), Informational Note

A 120 V single-phase circuit uses 12 AWG copper (6,530 cmil) carrying 20 A over a one-way length of 100 ft. Using VD = 2 × K × I × L ÷ cmil with K = 12.9, what is the approximate voltage drop?

• a.5.0 V (about 4.2%)
• b.3.9 V (about 3.3%)
• c.2.0 V (about 1.7%)
• d.7.9 V (about 6.6%)✓

VD = 2 × 12.9 × 20 × 100 ÷ 6,530 = 51,600 ÷ 6,530 ≈ 7.9 V, which is 7.9/120 ≈ 6.6%. The lower values would require either a shorter run or a larger conductor.

The circuit in the previous scenario has a voltage drop of about 6.6%, well above the recommended 3% for a branch circuit. What is the most appropriate corrective action?

• a.Leave it; 6.6% is acceptable
• b.Add a second ground rod
• c.Increase the breaker size to 30 A
• d.Increase the conductor size to reduce voltage drop✓

Increasing the conductor cross-sectional area (more circular mils) lowers the voltage drop, since VD is inversely proportional to cmil. Raising the breaker size does not reduce voltage drop (and may violate conductor ampacity), and grounding changes do not affect voltage drop.

A 240 V single-phase circuit uses 10 AWG copper (10,380 cmil) carrying 24 A over a one-way length of 150 ft, with K = 12.9. What is the approximate voltage drop and percentage?

• a.2.2 V, about 0.9%
• b.17.9 V, about 7.5%
• c.8.9 V, about 3.7%✓
• d.4.5 V, about 1.9%

VD = 2 × 12.9 × 24 × 150 ÷ 10,380 = 92,880 ÷ 10,380 ≈ 8.9 V, which is 8.9/240 ≈ 3.7%. The other options misplace the length, current, or divide by the wrong circular-mil value.

In the voltage-drop formula for a balanced 3-phase circuit, which multiplier replaces the factor of 2 used in single-phase calculations?

• a.2
• b.3
• c.1
• d.1.732✓

Three-phase voltage drop uses 1.732 (the square root of 3) in place of the single-phase factor of 2. Using 2 would be the single-phase form, and 1 or 3 are incorrect multipliers.

To reduce voltage drop on a long branch-circuit run without changing the load, what is the most effective method?

• a.Lower the conductor insulation temperature rating
• b.Add additional terminations along the run
• c.Increase the conductor cross-sectional area (more circular mils)✓
• d.Increase the overcurrent device rating

Voltage drop is inversely proportional to conductor circular mils, so using a larger conductor is the direct remedy. Increasing the breaker or changing insulation rating does not lower voltage drop, and extra terminations only add resistance and points of failure.

If the one-way length of a circuit run is doubled while current and conductor size stay the same, what happens to the voltage drop?

• a.It is halved
• b.It quadruples
• c.It stays the same
• d.It doubles✓

Voltage drop is directly proportional to conductor length, so doubling the length doubles the voltage drop. It does not stay constant or quadruple, and it certainly does not decrease.

Per 200.6(A), a grounded (neutral) conductor 6 AWG or smaller must be identified by which of the following?

• a.Red insulation
• b.Orange insulation
• c.Green insulation
• d.A continuous white or gray outer finish (or three white/gray stripes)✓

Section 200.6(A) requires 6 AWG and smaller grounded conductors to be white or gray, or to have three continuous white/gray stripes. Green is reserved for grounding, and red or orange are used for ungrounded (hot) conductors.2023 NEC §200.6(A)

Per 250.119, an equipment grounding conductor may be identified by which of the following?

• a.Gray insulation
• b.Blue insulation
• c.White insulation
• d.Green, green with yellow stripe, or bare✓

Section 250.119 permits equipment grounding conductors to be green, green with one or more yellow stripes, or bare. White and gray are reserved for grounded (neutral) conductors, and blue is used as an ungrounded conductor color.2023 NEC §250.119

Per 110.15, on a 4-wire delta-connected 120/240 V system, the high-leg (the conductor with the higher voltage to ground) must be identified by what color?

• a.Blue
• b.Orange✓
• c.Green
• d.White

Section 110.15 requires the high-leg conductor (about 208 V to ground) to be durably marked orange or by other effective means. White is for the neutral and green for grounding, and blue is a normal ungrounded color that would not warn of the high leg.2023 NEC §110.15

Which set of colors is NOT permitted for ungrounded (hot) conductors, because these colors are reserved for other uses?

• a.White, gray, and green✓
• b.Black and red
• c.Orange and yellow
• d.Blue and brown

White and gray are reserved for grounded (neutral) conductors and green (or green/yellow) for grounding, so none may be used for ungrounded conductors. Black, red, blue, brown, orange, and yellow are all acceptable ungrounded colors.2023 NEC §200.6

Per 210.5(C), where a building is supplied by more than one nominal voltage system, how must the ungrounded branch-circuit conductors be treated?

• a.They may be left unmarked
• b.Each system's ungrounded conductors must be identified (e.g., by color), with the means posted at each panelboard✓
• c.All systems may share the same color
• d.All must be black

Section 210.5(C) requires ungrounded conductors of each system to be identified by phase or line and system, with the identification method documented and readily available (posted) at each branch-circuit panelboard. Leaving them unmarked or using one color for all systems defeats the safety intent.2023 NEC §210.5(C)

Per 200.6(B), how may a grounded (neutral) conductor larger than 6 AWG be identified?

• a.It must be manufactured with white insulation only
• b.By orange insulation
• c.By wrapping green tape at each end
• d.By white/gray insulation, or by distinctive white/gray markings (such as tape) at each termination and accessible point✓

Section 200.6(B) allows grounded conductors larger than 6 AWG to be white or gray, or to be marked with distinctive white or gray encircling identification at terminations and where accessible. Green is for grounding and orange indicates a high leg, so neither identifies a neutral.2023 NEC §200.6(B)

Using NEC Table 430.250, what is the full-load current (FLC) of a 10 HP, three-phase, 460-volt squirrel-cage motor?

• a.11 A
• b.14 A✓
• c.21 A
• d.28 A

NEC Table 430.250 lists 14 A for a 10 HP 460 V three-phase motor; these table values (not nameplate amps) are used for conductor and overcurrent sizing. 28 A is the 230 V value, 21 A is a 15 HP motor, and 11 A is 7.5 HP at 460 V.2023 NEC Table 430.250

Per NEC Table 430.248, what is the full-load current of a 5 HP, single-phase, 230-volt motor?

• a.17 A
• b.40 A
• c.56 A
• d.28 A✓

Table 430.248 gives 28 A for a 5 HP single-phase 230 V motor. 56 A is the 115 V value for the same HP, 17 A is a 3 HP 230 V single-phase motor, and 40 A is a 7.5 HP 230 V motor.2023 NEC Table 430.248

A single continuous-duty 25 HP, 460 V, three-phase motor has an FLC of 34 A (Table 430.250). What minimum conductor ampacity is required for its branch circuit?

• a.34 A
• b.42.5 A✓
• c.46.75 A
• d.38.25 A

NEC 430.22 requires branch-circuit conductors for a single continuous-duty motor to be sized at 125% of FLC: 34 A x 1.25 = 42.5 A. 34 A ignores the 125% factor, 38.25 A uses 112.5%, and 46.75 A uses 137.5%.2023 NEC §430.22

A motor's nameplate shows a full-load current of 40 A and a service factor of 1.15. Under NEC 430.32(A)(1), what is the maximum overload device rating at 125% of nameplate FLA?

• a.40 A
• b.44 A
• c.50 A✓
• d.46 A

For a motor with a marked service factor of 1.15 or greater, 430.32(A)(1) permits overload protection up to 125% of the nameplate FLA: 40 x 1.25 = 50 A. 44 A is 110%, 46 A is 115% (used only for other motors), and 40 A applies no multiplier.2023 NEC §430.32

For a 20 HP, 460 V, three-phase motor (FLC 27 A), what is the maximum inverse-time circuit breaker rating for branch-circuit short-circuit and ground-fault protection, using the 250% value of Table 430.52?

• a.54 A
• b.67.5 A✓
• c.47.25 A
• d.81 A

Table 430.52 allows an inverse-time breaker at 250% of FLC: 27 x 2.50 = 67.5 A (then the next-standard-size rule of 430.52(C)(1) Ex. may apply). 47.25 A is 175% (dual-element fuse), 81 A is 300% (nontime-delay fuse), and 54 A is 200%.2023 NEC §430.52

Using the same 20 HP, 460 V motor (FLC 27 A), what is the maximum dual-element (time-delay) fuse permitted by Table 430.52 for branch-circuit short-circuit and ground-fault protection?

• a.67.5 A
• b.47.25 A✓
• c.33.75 A
• d.81 A

Table 430.52 permits a dual-element time-delay fuse at 175% of FLC: 27 x 1.75 = 47.25 A. 67.5 A is 250% (inverse-time breaker), 81 A is 300% (nontime-delay fuse), and 33.75 A is 125%.2023 NEC §430.52

A 5 HP, 230 V, three-phase motor has an FLC of 15.2 A. What is the maximum nontime-delay fuse permitted by Table 430.52 for branch-circuit protection?

• a.26.6 A
• b.45.6 A✓
• c.38 A
• d.121.6 A

A nontime-delay fuse may be sized up to 300% of FLC: 15.2 x 3.00 = 45.6 A. 26.6 A is 175% (dual-element fuse), 38 A is 250% (inverse-time breaker), and 121.6 A is 800% (instantaneous-trip breaker).2023 NEC §430.52

For the same 5 HP, 230 V motor (FLC 15.2 A), what is the maximum instantaneous-trip circuit breaker setting permitted by Table 430.52?

• a.38 A
• b.76 A
• c.121.6 A✓
• d.45.6 A

Table 430.52 permits an instantaneous-trip breaker up to 800% of FLC for most motors: 15.2 x 8 = 121.6 A. 45.6 A is 300%, 38 A is 250%, and 76 A is 500%.2023 NEC §430.52

When sizing branch-circuit conductors and short-circuit/ground-fault protection for a standard motor, which current value does the NEC require you to use?

• a.The service-factor amperes
• b.The nameplate full-load amperes
• c.The locked-rotor current
• d.The full-load current from Tables 430.247 through 430.250✓

NEC 430.6(A)(1) requires the table FLC values (430.247-430.250) for conductor and branch-circuit protection sizing. The nameplate FLA is used only for overload (running) protection, while locked-rotor and service-factor amps serve other purposes.2023 NEC §430.6

Which motor current rating is used to select the running overload (overcurrent) protection device?

• a.The locked-rotor current from Table 430.251
• b.The motor nameplate full-load amperes✓
• c.The Table 430.250 full-load current
• d.250% of the full-load current

NEC 430.6(A)(2) and 430.32 base overload protection on the motor's nameplate full-load amperes, because overloads protect the actual motor. The table FLC is used for conductors and short-circuit protection, not overload sizing.2023 NEC §430.32