Texas Master Electrician NEC Knowledge Portion

Key Concepts

• Scope of Article 90 (90.1): Article 90 covers "use and application, arrangement, and enforcement of this Code," the expression of mandatory, permissive, and nonmandatory text, guidance on examination of equipment and wiring planning, and "the use and expression of measurements."
• Purpose (90.2(A) Practical Safeguarding): "The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. This Code is not intended as a design specification or an instruction manual for untrained persons."
• Adequacy (90.2(B) in the 2023 text; cited as 90.2(C) in the 2026 arrangement): Compliance and proper maintenance "result in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use."
• Installations covered (90.2(C)): public and private premises including buildings,…

Key Concepts

Service disconnect location and marking. For one- and two-family dwellings, service disconnects must be installed in a readily accessible outdoor location either on the dwelling unit or within sight of it [230.70(A)(1)]. For all other occupancies, the disconnect goes in a readily accessible location outside the building or inside nearest the point of entrance of the service conductors [230.70(A)(2)]. Disconnects shall not be installed in bathrooms [230.70(A)(3)]. All service disconnects are marked "SERVICE DISCONNECT" [230.70(B)(1)]; one- and two-family dwelling enclosures are additionally marked "EMERGENCY DISCONNECT" on the outside front, red background with white text, letters at least 13 mm (½ in.) high [230.70(B)(2)].

Key Concepts

• Scope. Article 215 covers installation, overcurrent protection, minimum size and ampacity of feeders not over 1000 volts ac or 1500 volts dc, nominal (215.1).
• Minimum size. Feeder conductors shall have an ampacity not less than the larger of 215.2(A)(1) or (A)(2) and shall comply with 110.14(C) (215.2(A)). Under 215.2(A)(1), where a feeder supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum feeder conductor size shall have an ampacity not less than the noncontinuous load plus 125 percent of the continuous load. Under 215.2(A)(2), ampacity must be not less than the maximum load after adjustment or correction factors per 310.14.
• Exceptions to the 125% rule (215.2(A)(1)). Exception No. 1 — assembly, including the feeder overcurrent devices, listed for operation at 100 percent of its rating: continuous plus noncontinuous load. Exception No.…

Key Concepts

Sizing branch-circuit conductors (210.19). Conductors must have an ampacity not less than the larger of: (1) noncontinuous load plus 125 percent of the continuous load, per 310.14, and (2) the maximum load to be served after applying adjustment or correction factors per 310.15 — and they must comply with 110.14(C) for equipment terminations [210.19(A), 210.19(A)(2)].

• Exception to (1): if the assembly, including the branch-circuit OCPDs, is listed for operation at 100 percent of its rating, ampacity may be the sum of continuous plus noncontinuous load [210.19(A)(1), Exception].
• Exception to (1) and (2): where a portion of a branch circuit is connected at both supply and load ends to separately installed pressure connections as covered in 110.14(C)(2), ampacity per 310.15 not less than the sum of continuous plus noncontinuous load is permitted; no portion may extend…

Key Concepts

Scope and voltage limits - Wiring methods specified in Chapter 3 shall be used for 1000 volts ac, 1500 volts dc, nominal, or less where not specifically limited elsewhere in Chapter 3 — 300.2(A). - Metric designators and trade sizes are for identification purposes only and are not actual dimensions — 300.1(C) and Table 300.1(C).

Conductors - Single conductors specified in Table 310.4(1) are permitted only as part of a recognized Chapter 3 wiring method. Exception: individual conductors are permitted where installed as separate overhead conductors in accordance with 225.6 — 300.3(A). - Conductors 8 AWG and larger installed in raceways shall be stranded, unless specifically permitted or required elsewhere to be solid — 310.5(C). - Conductors may be connected in parallel only in sizes 1/0 AWG and larger — 310.10(G)(1). Paralleled conductors must be the same…

Key Concepts

Switches (Article 404) - Switches and circuit breakers used as switches must be operable from a readily accessible place, with the center of the grip of the operating handle, in its highest position, not more than 2.0 m (6 ft 7 in.) above the floor or working platform — 404.8(A). Exceptions: busway installations, devices adjacent to the motor/appliance they supply, and hookstick-operable isolating switches. - A snap switch shall not be grouped or ganged with other snap switches, receptacles, or similar devices unless the voltage between adjacent devices does not exceed 300 volts, or identified, securely installed barriers are provided — 404.8(B). - AC/DC general-use snap switch: inductive loads shall not exceed 50 percent of the switch ampere rating at the applied voltage; resistive loads may go to the full ampere rating — 404.14(B). - **AC general-use…

Key Concepts

Which current do you use? Per 430.6(A)(1), the values in Table 430.247 through Table 430.250 — not the nameplate current — are used to determine conductor ampacity, current ratings of switches, and branch-circuit short-circuit and ground-fault (SC/GF) protection ratings. Per 430.6(A)(2), the nameplate current rating is used for separate motor overload protection (and for low-speed <1200 RPM, high-torque, canned-pump, and multispeed motors).

Branch-circuit conductors (430.22). Conductors supplying a single motor in a continuous duty application shall have an ampacity of not less than 125 percent of the motor full-load current rating as determined by 430.6(A)(1). Special cases: wye-start/delta-run conductors between controller and motor 72 percent (430.22(C)); part-winding connected motor between controller and motor 62.5 percent (430.22(D)); dc motor from single-phase rectified supply, 190 percent (half-wave) or 150 percent (full-wave) (430.22(A)).

Key Concepts

Switches — rating and use (Article 404) - An ac general-use snap switch may control: resistive and inductive loads not exceeding the switch's ampere rating at the applied voltage; tungsten-filament lamp loads not exceeding the rating at 120 volts; electric-discharge lamp loads not exceeding the marked ampere/voltage rating; motor loads not exceeding 80 percent of the ampere rating of the switch at its rated voltage; and electronic ballasts, self-ballasted lamps, CFL and LED loads not exceeding 20 amperes — 404.14(A). - An ac/dc general-use snap switch may control resistive loads up to the switch rating, but inductive loads only up to 50 percent of the rating; switches rated in horsepower are suitable for motor loads within their rating — 404.14(B). - Switches shall be listed and marked with their ratings — 404.14; marked with current, voltage and,…

Key Concepts

Classification of locations (500.5) - Class I locations: flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors are or may be present in the air in quantities sufficient to produce explosive or ignitible mixtures — 500.5(B). - Class I, Division 1: ignitible concentrations can exist under normal operating conditions, or might exist frequently because of repair/maintenance or leakage, or could be released by breakdown/faulty operation with simultaneous equipment failure — 500.5(B)(1). - Class II locations are hazardous because of the presence of combustible dust — 500.5(C). - Areas designated hazardous (classified) or determined to be unclassified must be documented on an area classification drawing and other associated documentation, available to the AHJ and those authorized to design, install, inspect, maintain, or operate equipment — 500.4.

Key Concepts

• Maximum PV dc voltage. PV system dc circuits shall not exceed 1000 volts within or originating from arrays located on or attached to buildings and PV system dc circuits inside buildings; they shall not exceed 600 volts on or in one- and two-family dwellings. Circuits exceeding 1000 volts comply with 690.31(G). (690.7; 690.7(1)(2))
• Voltage calculation for PV source circuits. Maximum dc voltage is the sum of the series-connected module rated open-circuit voltages corrected for the lowest expected ambient temperature, using (1) the module's listed temperature coefficients, (2) Table 690.7(A) for crystalline/multicrystalline silicon, or (3) a documented, stamped design by a licensed professional electrical engineer. (690.7(A))
• Voltage marking. A permanent readily visible label showing the highest maximum dc voltage must be provided at the dc PV system disconnecting means, the PV system electronic power conversion…