Texas Journeyman Electrician NEC Knowledge Portion

Hard conversion (the NEC default per 90.9(B), except as provided in 90.9(C)) changes dimensions or properties into new sizes, while soft conversion is a direct mathematical conversion that does not change actual dimensions and is permitted where the actual measured size differs from the nominal size and trade size designators are used.

A 12 AWG THWN copper conductor has a 25-ampere ampacity in the 75°C column at 30°C ambient, whereas the commonly cited 20 amperes is the maximum overcurrent protection allowed for 12 AWG, not its table ampacity.

For transformers rated 1000 volts or less with primary current of 9 amperes or more, Table 450.3(B) limits primary overcurrent protection to 125% of rated current when only primary protection is used, but permits up to 250% when both primary and secondary protection are provided.

Per 700.12(C) the emergency power source must supply the total load for not less than 2 hours unless used for emergency illumination under 700.12(C)(4) or unit equipment under 700.12(H); the 1½-hour minimum (with voltage not below 87½% of nominal) applies specifically to storage batteries and UPS supplying emergency illumination.

Table 300.5(A) requires 600 mm (24 in.) cover in all locations not otherwise specified, but allows 450 mm (18 in.) for one- and two-family dwelling driveways and outdoor parking areas used only for dwelling-related purposes, and 300 mm (12 in.) for residential branch circuits rated 120 volts or less with GFCI protection and maximum 20-ampere overcurrent protection.

Per 90.3 Chapters 1, 2, 3, and 4 apply generally to all electrical installations; Chapters 5, 6, and 7 apply to special occupancies, equipment, or conditions and may supplement or modify Chapters 1 through 7; Chapter 8 covers communications systems and is not subject to Chapters 1 through 7 except where specifically referenced in Chapter 8; Chapter 9 consists of tables applicable as referenced.

Conductors between controller and motor must be not less than 72% of motor FLC for wye-start/delta-run per 430.22(C) (58% × 1.25), versus not less than 62.5% for part-winding connected motors per 430.22(D) (50% × 1.25).

A single continuous-duty motor's branch-circuit conductors must be at least 125% of that motor's full-load current, while feeder conductors supplying several motors must be at least 125% of the highest rated motor's FLC plus the sum of the full-load currents of all other motors.

EGCs in flexible cords may be sized the same as the circuit conductors in the cord — as small as 18 AWG copper for certain cord types in Table 400.4 — because 250.122(F) permits sizing per 400.23, whereas Table 250.122 otherwise requires a 14 AWG minimum.

Rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, and electrical metallic tubing are exempt from steel plate protection at notches (300.4(A)(2) Ex. 1) and when run parallel to framing members within 32 mm (1-1/4 in.) of the edge (300.4(D) Ex. 1), while nonmetallic-sheathed cable, Type MC cable, and flexible metal conduit are not exempt.

The higher ampacity may be applied to a whole circuit only if the lower-ampacity portion does not exceed the lesser of 3.0 m (10 ft) or 10 percent of the total circuit, whereas the separate 600 mm (24 in.) rule exempts short raceways from adjustment factors entirely.

The MCC marking per 110.21 must be plainly visible after installation and include the common power bus current rating and the MCC short-circuit rating, while the available fault current and the date of its calculation are documented and made available rather than required as nameplate marking.

Per 220.14(I) each single or each multiple receptacle on one yoke is calculated at not less than 180 volt-amperes; the 90 volt-ampere value applies only to a single piece of equipment consisting of a multiple receptacle comprised of four or more receptacles.