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

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)