CSLB C-10 Electrical Contractor

B. 65 amps (75°C column)

NEC 110.14(C) requires conductor ampacity to be selected based on the lowest temperature rating of any connected termination, equipment, or conductor. Since the terminals are rated 75°C, the conductor must be sized using the 75°C column of Table 310.16, which gives 65A for 6 AWG copper, even though the insulation itself is rated 90°C.

B. 78.2 amperes

NEC 430.110(A) requires the disconnecting means for a motor circuit to have an ampere rating of at least 115% of the motor's full-load current: 68A x 1.15 = 78.2A. A disconnect switch rated at least 80A (next standard switch size) would be selected in practice, but the calculated minimum is 78.2A.

D. 2 inch

Total conductor area = (3 × 0.3237) + 0.0824 = 0.9711 + 0.0824 = 1.0535 in². A 1-1/2-inch EMT allows only 0.814 in² at 40% fill (insufficient). A 2-inch EMT allows 1.342 in² at 40% fill, which comfortably exceeds the 1.0535 in² required, making it the minimum acceptable size.

D. GFCI protection

CEC/NEC 210.8(A)(6) requires GFCI protection for all 125-volt, 15- and 20-ampere receptacles installed to serve kitchen countertop surfaces in dwelling units.

B. 12 inches

NEC 334.30 requires NM cable to be secured within 12 inches of every box, cabinet, or fitting where a cable clamp is used, and at intervals not exceeding 4.5 feet thereafter. This prevents strain on terminations and protects the cable from mechanical damage.

A. 360°

NEC 358.26 limits the total bends in an EMT run between pull points (such as boxes or conduit bodies) to 360 degrees, equivalent to four 90-degree bends, to allow conductors to be pulled without excessive damage.

B. The interlocked metal armor is not watertight or corrosion-resistant for direct burial

Standard Type MC cable has an interlocked metallic armor that is not sealed against moisture and is subject to corrosion, so it is unsuitable for direct burial or wet locations unless specifically listed and jacketed for that use.

D. 15 amperes

125% x 9.4A = 11.75A. Since this does not correspond to a standard overcurrent device size, NEC 450.3(B) and 240.6(A) permit rounding up to the next higher standard rating, which is 15 amperes.

A. 8 AWG

NEC Table 250.122 sizes the equipment grounding conductor based on the rating of the overcurrent device protecting the circuit, not the actual load. For overcurrent protection rated up to 100A, the minimum copper EGC size is 8 AWG.

D. 3/4 inch

NEC Annex C Table C.1 lists the maximum number of conductors permitted in EMT trade sizes. For 10 AWG THWN, 1/2 inch EMT permits only 4 conductors, while 3/4 inch EMT permits 8 conductors. Since 6 conductors exceed the 1/2 inch capacity but fit within 3/4 inch, the minimum trade size is 3/4 inch.

D. Concentric knockouts can leave paint or a poor electrical connection, preventing reliable bonding through the ring alone

Where concentric or eccentric knockouts are punched, the reduced material in the rings may not provide a reliable low-impedance path to ground. NEC 250.92(B) requires bonding jumpers or bonding-type locknuts/bushings in these cases to ensure an effective ground-fault current path at service equipment.

D. A bonding jumper must be installed to bypass the reducing washers

NEC 250.92(B) does not recognize reducing washers, oversized knockouts with locknuts alone, or standard locknuts/bushings as reliable bonding methods at service equipment. When reducing washers are used, a bonding jumper must be installed to ensure a low-impedance path for fault current, since normal threaded connections cannot be relied upon there.

D. Concealed within a masonry wall of a building three stories or less in height

ENT is a flexible, corrugated nonmetallic raceway intended for concealed use in walls, floors, and ceilings of buildings not exceeding three floors above grade. It is not permitted in exposed locations subject to physical damage, direct burial without concrete encasement, or in hazardous locations.

C. 450 amps

When conductors are installed in parallel under NEC 310.10(H), they must be identical in length, material, size, insulation, and termination, and the total ampacity equals the sum of each individual conductor's ampacity. Two 225A conductors in parallel yield 225A + 225A = 450A, which is sufficient to serve the 400A load.

A. 13.5V, exceeds the limit

VD = (1.732 × 12.9 × 50 × 200) / 16,510 ≈ (1.732 × 12.9 = 22.34; 22.34 × 50 = 1,117; 1,117 × 200 = 223,400; 223,400 / 16,510 ≈ 13.5V). Since 13.5V far exceeds the recommended 3% limit of 6.24V (208V × 0.03), the 8 AWG conductors are undersized for this run and a larger conductor is needed.

A. GFCI protection only

NEC 210.8(A)(3) requires GFCI protection for all 125-volt, 15- and 20-ampere receptacles installed outdoors at dwelling units, regardless of height above grade.

B. Rigid metal conduit (RMC) or intermediate metal conduit (IMC) with threaded, explosion-proof sealed fittings

NEC 501.10(A) requires that wiring methods in Class I, Division 1 locations be threaded rigid metal conduit or threaded intermediate metal conduit, with boxes, fittings, and joints made explosion-proof and sealed per 501.15 to prevent ignition of flammable vapors.

A. 15.75 cubic inches

Conductors: 4 × 2.25 = 9.0. Grounding conductors (all count as one, based on largest): 1 × 2.25 = 2.25. Device yoke (counts as two volume allowances, based on largest conductor): 2 × 2.25 = 4.5. Total = 9.0 + 2.25 + 4.5 = 15.75 cubic inches.

C. 15

The sum of cable diameters cannot exceed the tray width: 18 in ÷ 1.2 in per cable = 15 cables. Any additional cable would cause the total diameter sum to exceed the 18-inch tray width, violating the rule for large single-conductor cables in cable tray.

C. Every 10 feet

NEC 358.30 requires EMT to be securely fastened within 3 feet of every outlet box, junction box, cabinet, or termination, and at intervals not exceeding 10 feet along the remaining length of the run.

D. Apply an approved antioxidant compound to the conductor before making the connection

Aluminum conductors form an oxide layer when exposed to air, which increases resistance and heat at terminations. Manufacturers and the NEC recommend applying an approved antioxidant compound during termination on devices listed for aluminum use to maintain a low-resistance, reliable connection.

D. 1/0 AWG copper

NEC Table 250.66 specifies that for copper service-entrance conductors larger than 350 kcmil through 600 kcmil, the minimum copper grounding electrode conductor size is 1/0 AWG. Since 400 kcmil falls within this range, a 1/0 AWG copper GEC is required.

D. Type AC cable

Type AC (armored) cable includes an internal aluminum bonding strip in contact with the spiral steel armor to ensure a low-impedance grounding path, as required by NEC 320.108. MC cable instead typically includes a separate, full-sized insulated or bare equipment grounding conductor rather than relying on a thin bonding strip.

D. Nipples 24 inches or less allow 60% fill with no adjustment factors; conductor area (0.0532 in²) is well under the 0.1824 in² limit, so it complies

NEC Chapter 9, Note 4 to the Tables permits conduit or tubing nipples 24 inches or less in length to be filled to 60% of their cross-sectional area without applying the ampacity adjustment factors of 310.15(C)(1). Here, 60% of 0.304 in² = 0.1824 in², and the four 12 AWG THHN conductors total only 0.0532 in², well within the allowed area.

C. 40 amperes

The 10-foot tap rule requires tap conductor ampacity to be not less than 1/10 of the feeder OCPD rating (400A x 0.10 = 40A) and not less than the rating of the device it supplies (40A panel). Both conditions point to a minimum of 40A, and the 8-foot tap length satisfies the 10-foot maximum requirement.