CSLB General Building (B) — All Questions

A box contains six 12 AWG conductors, one internal cable clamp and one duplex receptacle, all 12 AWG. What minimum box volume is required?

• a.20.25 cubic inches✓
• b.13.5 cubic inches
• c.18.0 cubic inches
• d.22.5 cubic inches

Count six conductors, one allowance for all internal clamps and two allowances for the device yoke, giving 9 volume allowances. Each 12 AWG allowance is 2.25 cubic inches, so 9 x 2.25 = 20.25 cubic inches. Counting only the conductors gives 13.5 cubic inches, and forgetting that a yoke counts as two conductors gives 18.0 cubic inches.2023 NEC §314.16(B)

A device box has three 14-2 NM cables with equipment grounding conductors entering through internal clamps, and one single-pole switch is installed. What minimum box volume is required?

• a.20.0 cubic inches✓
• b.18.0 cubic inches
• c.16.0 cubic inches
• d.22.5 cubic inches

Six insulated conductors count individually, all equipment grounding conductors together count as one, all internal clamps together count as one, and the switch yoke counts as two, for 10 allowances. At 2.00 cubic inches for 14 AWG, 10 x 2.00 = 20.0 cubic inches. The 18.0 answer misses one allowance, 16.0 omits both the clamp and grounding allowances, and 22.5 uses the 12 AWG allowance by mistake.2023 NEC §314.16(B)

What is the minimum trade size of EMT required for nine 12 AWG THHN conductors?

• a.One-half inch✓
• b.Three-quarter inch
• c.One inch
• d.One and one-quarter inch

Annex C, Table C1 shows that one-half inch EMT accepts nine 12 AWG THHN conductors, exactly meeting the requirement. Three-quarter inch EMT holds sixteen and one inch holds twenty-six, so both are larger than the minimum. Annex C may be used directly whenever all conductors are the same size and insulation type.2023 NEC Annex C, Table C1

When more than two conductors are installed in a raceway, what is the maximum permitted percentage of the raceway cross-sectional area they may occupy?

• a.53 percent
• b.31 percent
• c.40 percent✓
• d.60 percent

Chapter 9, Table 1 allows 53 percent fill for one conductor, 31 percent for exactly two conductors and 40 percent for three or more. The 60 percent value applies only to a nipple not exceeding 24 inches in length between boxes or enclosures.2023 NEC Chapter 9, Table 1

A short raceway nipple no longer than 24 inches connects two enclosures. What fill percentage is permitted?

• a.31 percent
• b.40 percent
• c.53 percent
• d.60 percent✓

Notes to Chapter 9, Table 1 permit a nipple not exceeding 24 inches in length to be filled to 60 percent of its total cross-sectional area, because heat buildup and pulling friction are both minimal over such a short run. The 40, 53 and 31 percent values are the normal fills for three or more, one, and two conductors respectively.2023 NEC Chapter 9, Table 1, Note 4

Four 3/0 AWG THWN conductors, each 0.2679 square inch in area, are pulled into rigid metal conduit. What is the minimum trade size?

• a.2 inch✓
• b.1 and 1/2 inch
• c.2 and 1/2 inch
• d.1 and 1/4 inch

Total conductor area is 4 x 0.2679 = 1.0716 square inches, and with more than two conductors only 40 percent of the raceway may be filled. One and one-half inch RMC allows only about 0.81 square inch at 40 percent, which is too little, while 2 inch RMC allows about 1.34 square inches and is adequate. Two and one-half inch is larger than the calculated minimum.2023 NEC Chapter 9, Table 4

What is the minimum cover for a direct-buried UF cable installed in a residential yard on a 120-volt, 20-ampere circuit that is NOT GFCI protected?

• a.18 inches
• b.24 inches✓
• c.12 inches
• d.6 inches

Direct-buried cables and conductors under all locations not otherwise covered require 24 inches of cover. The 12-inch reduction applies only to residential branch circuits rated 120 volts or less, 20 amperes or less, and provided with GFCI protection, so removing the GFCI removes the reduction. The 6-inch and 18-inch values belong to metal and nonmetallic raceways respectively.2023 NEC Table 300.5

What is the minimum burial cover for rigid metal conduit installed underground in a location not otherwise specified?

• a.18 inches
• b.12 inches
• c.6 inches✓
• d.24 inches

Rigid metal conduit and intermediate metal conduit are permitted at 6 inches of cover because the metal wall provides its own physical protection. Nonmetallic raceways listed for direct burial require 18 inches, direct-buried cable requires 24 inches, and 12 inches applies to GFCI-protected residential branch circuits.2023 NEC Table 300.5

What is the minimum burial cover for a nonmetallic raceway listed for direct burial without concrete encasement, installed under a lawn?

• a.18 inches✓
• b.6 inches
• c.24 inches
• d.12 inches

Listed nonmetallic raceways buried without concrete encasement require 18 inches of cover in locations not otherwise specified. Metal conduit needs only 6 inches, direct-buried cable needs 24 inches, and 12 inches applies to GFCI-protected 120-volt residential branch circuits.2023 NEC Table 300.5

A GFCI-protected 120-volt, 20-ampere residential branch circuit is direct buried in a yard. What is the minimum cover?

• a.18 inches
• b.6 inches
• c.12 inches✓
• d.24 inches

Residential branch circuits rated 120 volts or less and 20 amperes or less that have GFCI protection may be buried with only 12 inches of cover, because a ground fault from a dig-in will clear immediately. Without GFCI protection the general 24-inch requirement applies, and the 6- and 18-inch values belong to metal and nonmetallic raceways.2023 NEC Table 300.5

How must electrical metallic tubing be secured and supported on a normal horizontal run?

• a.Secured within 3 feet of each box and supported at least every 10 feet✓
• b.Secured within 12 inches of each box and supported every 4 and 1/2 feet
• c.Secured within 3 feet of each box and supported every 6 feet
• d.Support is required only every 10 feet with no requirement near boxes

EMT must be securely fastened within 3 feet of every box, cabinet or termination and supported at intervals not exceeding 10 feet. The 12-inch and 4 and 1/2-foot figures belong to Type NM and Type AC cable, and the 6-foot interval is the MC cable support spacing.2023 NEC §358.30(A)

How must Type NM cable be supported where it enters a box equipped with cable clamps?

• a.Secured within 8 inches of the box and supported every 6 feet
• b.Secured within 12 inches of the box and supported at least every 4 and 1/2 feet✓
• c.Secured within 3 feet of the box and supported every 10 feet
• d.Secured within 12 inches of the box and supported every 6 feet

Type NM cable is secured within 12 inches of each box, cabinet or fitting and supported at intervals not exceeding 4 and 1/2 feet. The 8-inch figure applies to a single-gang nonmetallic box without clamps, the 3-foot and 10-foot values are EMT, and the 6-foot interval belongs to MC cable.2023 NEC §334.30

At what maximum interval must Type MC cable be supported and secured?

• a.Every 3 feet, and within 12 inches of every termination
• b.Every 4 and 1/2 feet, and within 12 inches of every termination
• c.Every 10 feet, and within 3 feet of every termination
• d.Every 6 feet, and within 12 inches of every termination✓

Type MC cable is secured at intervals not exceeding 6 feet and within 12 inches of every box, cabinet or fitting where the cable terminates. The 4 and 1/2-foot interval belongs to Types NM and AC, and the 10-foot interval belongs to EMT and other rigid raceways.2023 NEC §330.30

At what maximum interval must Type AC cable be supported?

• a.Every 6 feet
• b.Every 4 and 1/2 feet✓
• c.Every 10 feet
• d.Every 3 feet

Type AC armored cable is supported at intervals not exceeding 4 and 1/2 feet and secured within 12 inches of each termination. The 6-foot figure is for Type MC cable and 10 feet is for EMT, so mixing the cable types is the usual source of error here.2023 NEC §320.30

What is the maximum support spacing for a 1-inch trade size rigid PVC conduit?

• a.6 feet
• b.5 feet
• c.3 feet✓
• d.10 feet

PVC expands and sags with temperature, so support spacing depends on trade size: one-half through 1 inch is supported every 3 feet, 1 and 1/4 through 2 inch every 5 feet, and larger sizes at progressively longer intervals. The 10-foot spacing belongs to EMT and rigid metal conduit, which are far stiffer.2023 NEC §352.30(B)

What is the maximum total amount of bend permitted in one run of EMT between pull points?

• a.270 degrees
• b.180 degrees
• c.360 degrees✓
• d.540 degrees

No more than the equivalent of four quarter bends, or 360 degrees total, is permitted between pull points such as conduit bodies and boxes, because friction rises sharply with each bend. The same 360-degree limit appears in the articles for rigid metal conduit and PVC, so it is worth memorizing once.2023 NEC §358.26

A cable passes through a bored hole in a wood stud. If the edge of the hole is less than 1 and 1/4 inches from the nearest edge of the stud, what is required?

• a.The cable must be rerouted through a notch instead
• b.A steel plate or bushing at least 1/16 inch thick installed to protect the cable✓
• c.A listed nonmetallic sleeve of any thickness
• d.Nothing additional, provided the cable is Type MC

When the required 1 and 1/4-inch setback cannot be maintained, a steel plate, sleeve or bushing at least 1/16 inch thick must cover the area of the wire so a drywall screw or nail cannot reach it. Notching is more damaging to the stud and creates the same exposure, and nonmetallic sleeves do not satisfy this rule.2023 NEC §300.4(A)(1)

A pull box is used for a straight pull, and the largest raceway entering it is 3 inch trade size. What is the minimum required length of the box in the direction of the pull?

• a.18 inches
• b.24 inches✓
• c.12 inches
• d.36 inches

For straight pulls, the box length must be at least eight times the trade size of the largest raceway: 8 x 3 = 24 inches. The 18-inch answer uses a factor of six, which applies to angle and U pulls, and 12 inches uses a factor of four that appears nowhere in the rule.2023 NEC §314.28(A)(1)

An angle pull box has one 2-inch raceway and one 1-inch raceway entering the same wall, with conductors turning 90 degrees. What is the minimum distance from that wall to the opposite wall?

• a.24 inches
• b.12 inches
• c.16 inches
• d.13 inches✓

For angle pulls the distance is six times the trade size of the largest raceway plus the sum of the diameters of the other raceways on the same wall: (6 x 2) + 1 = 13 inches. The 12-inch answer forgets to add the additional raceway, and 24 inches applies the straight-pull factor of eight.2023 NEC §314.28(A)(2)

How must liquidtight flexible metal conduit be secured on a normal run?

• a.Within 12 inches of each box and at intervals not exceeding 6 feet
• b.Within 3 feet of each box and at intervals not exceeding 10 feet
• c.Within 12 inches of each box or fitting and at intervals not exceeding 4 and 1/2 feet✓
• d.Support is not required for lengths of 6 feet or less in any application

LFMC is secured within 12 inches of each box, cabinet or fitting and supported at intervals not exceeding 4 and 1/2 feet. Certain short lengths used for flexibility or for connections to luminaires are exempt, but that exemption is narrow and does not apply to ordinary runs, and the 10-foot spacing belongs to rigid raceways.2023 NEC §350.30(A)

How many 12 AWG conductors may be installed in a 4-11/16 inch by 2-1/8 inch square box with a volume of 42.0 cubic inches, assuming no clamps, devices or fittings?

• a.21
• b.20
• c.16
• d.18✓

Each 12 AWG conductor requires 2.25 cubic inches, so 42.0 / 2.25 = 18.67, and the count must be rounded down to 18 whole conductors. The 21-conductor answer uses the 14 AWG allowance of 2.00 cubic inches, and 20 comes from rounding up rather than down.2023 NEC §314.16(A)

Direct-buried conductors emerging from grade must be protected by an approved enclosure or raceway from below grade to what height?

• a.8 feet above finished grade✓
• b.6 feet above finished grade
• c.10 feet above finished grade
• d.4 feet above finished grade

Protection must extend from below grade to at least 8 feet above finished grade, and the underground portion must reach at least 18 inches below grade. Six feet leaves the conductors within easy reach of damage, and neither 4 nor 10 feet is the code value.2023 NEC §300.5(D)(1)

What is the maximum fill percentage when exactly two conductors are installed in a raceway?

• a.40 percent
• b.31 percent✓
• c.53 percent
• d.60 percent

Two conductors are limited to 31 percent fill, a lower figure than the 40 percent allowed for three or more, because two round conductors of similar size can jam in a bend and damage insulation during the pull. One conductor may fill 53 percent, and 60 percent applies only to a nipple 24 inches or shorter.2023 NEC Chapter 9, Table 1

What is the minimum trade size of EMT required for twenty-four 12 AWG THHN conductors?

• a.One inch✓
• b.Three-quarter inch
• c.One and one-quarter inch
• d.One and one-half inch

Annex C, Table C1 shows one inch EMT accepts twenty-six 12 AWG THHN conductors, so twenty-four fit. Three-quarter inch holds only sixteen and is too small, while one and one-quarter inch holds far more than needed. Remember that twenty-four current-carrying conductors would also trigger a 45 percent ampacity adjustment.2023 NEC Annex C, Table C1

Conductors installed in an underground raceway in a wet location must have which characteristic?

• a.A nylon jacket, which by itself qualifies the conductor for wet locations
• b.Any thermoplastic insulation, since the raceway keeps water out
• c.Insulation rated 90 degrees C, regardless of wet-location listing
• d.Insulation listed for use in wet locations, such as THWN or THWN-2✓

Raceways in underground and other wet locations are considered wet inside, so the conductors must carry a wet-location listing such as THWN, THWN-2 or XHHW. The W in the type designation is what matters; plain THHN without the dual THWN-2 marking is a dry- and damp-location conductor, and a temperature rating or nylon jacket alone does not confer a wet-location listing.2023 NEC §310.10(C)