Mississippi Master Electrician

Key Concepts

Code arrangement and enforceability (Article 90). Chapters 1–4 apply generally; Chapters 5, 6, and 7 apply to special occupancies, equipment, or conditions. Chapter 8 (Communications Systems) is not subject to the requirements of Chapters 1 through 7 except where specifically referenced in Chapter 8 (NEC 90.3). Mandatory rules are characterized by "shall" or "shall not" (NEC 90.5(A)); permissive rules use "shall be permitted" or "shall not be required" (NEC 90.5(B)). Informational notes are explanatory only and are not enforceable (NEC 90.5(C)). The NEC does not cover installations in ships, watercraft other than floating buildings, railway rolling stock, aircraft, or automotive vehicles other than mobile homes and recreational vehicles (NEC 90.2(B)(1)).

Service, Feeders, and Branch Circuits (10 questions, 12%)

Key Concepts

Dwelling branch circuits. Two or more 20-ampere small-appliance branch circuits are required for all receptacle outlets specified by 210.52(B) [210.11(C)(1)]. Those circuits serve all wall, floor, and countertop outlets plus refrigeration equipment [210.52(B)(1)], and countertop receptacles must be supplied by not fewer than two small-appliance branch circuits [210.52(B)(3)]. A separate 20-ampere laundry circuit [210.11(C)(2)], bathroom circuit [210.11(C)(3)], and garage circuit [210.11(C)(4)] are also required.

Ratings and conductors. For household electric ranges rated 8¾ kW or more, the minimum branch-circuit rating is 40 amperes [210.19(A)(3)]. Branch circuits larger than 50 amperes shall supply only nonlighting outlet loads [210.23(D)]. Ratings for circuits other than individual branch circuits are 15, 20,…

Key Concepts

• Effective ground-fault current path: The path must create a low-impedance circuit capable of safely carrying the maximum ground-fault current likely to be imposed; "The earth shall not be considered as an effective ground-fault current path" (250.4(A)(5); also 250.4(B)(4) for ungrounded systems).
• Objectionable current: If multiple grounding connections cause objectionable current and 250.4(A)(5) or (B)(4) are still met, permitted alterations are: discontinue one or more but not all connections, change locations, interrupt continuity of the path, or take other approved action (250.6(B)).
• Connections: Permitted means include listed pressure connectors, terminal bars, exothermic welding, and machine screw-type fasteners engaging not less than two threads (250.8(A)). Devices depending solely on solder are prohibited (250.8(B)). Nonconductive coatings (paint,…

Mississippi Master Electrician

Key Concepts

Minimum conductor size and material (310.3) - Minimum size for voltage ratings up to and including 2000 volts: 14 AWG copper or 12 AWG aluminum or copper-clad aluminum, except as permitted elsewhere in the Code — 310.3(A). - Conductors shall be aluminum, copper-clad aluminum, or copper unless otherwise specified. Solid aluminum conductors 8, 10, and 12 AWG shall be made of an AA-8000 series electrical grade aluminum alloy — 310.3(B). - Where installed in raceways, conductors 8 AWG and larger shall be stranded, unless specifically permitted or required elsewhere to be solid — 310.3(C). - Conductors not specifically permitted to be covered or bare shall be insulated — 310.3(D).

Key Concepts

• Box fill (314.16(B)) — Volumes from (B)(1) through (B)(5) are added. Conductor fill uses Table 314.16(B); a 12 AWG conductor requires 2.25 in.³ (36.9 cm³). Internal cable clamps get a single allowance based on the largest conductor in the box (314.16(B)(2)). Each yoke or strap with one or more devices gets a double allowance based on the largest conductor connected to a device on that yoke (314.16(B)(4)). Up to four EGCs get a single allowance, with a ¼ allowance for each additional one (314.16(B)(5)).
• Conduit bodies (314.16(C)(1)) — A conduit body enclosing 6 AWG or smaller must have a cross-sectional area not less than twice that of the largest conduit or tubing it can attach…

Key Concepts

Commercial garages (Article 511) - Parking garages used only for parking or storage shall be permitted to be unclassified — 511.3(A). - A Class I location shall not extend beyond an unpierced wall, roof, or other solid partition that has no openings — 511.3. - Areas adjacent to classified locations where flammable vapors are not likely to be released (stock rooms, switchboard rooms) are unclassified where mechanically ventilated at four or more air changes per hour, designed with positive air pressure, or effectively cut off by walls/partitions — 511.3(E)(1); Table 511.3(C). - In major repair garages, the entire space within any pit, belowgrade work area, or subfloor work area that is not ventilated is Class I, Division…

Key Concepts

Scope of the construction power rules. Subpart V "covers the construction of electric power transmission and distribution lines and equipment," including erection of new lines and the "alteration, conversion, and improvement" of existing ones (§1926.950(a)(1)(i)). An employer complying with §1910.269 "will be considered in compliance with requirements in this subpart that do not reference other subparts of this part" (Note to §1926.950(a)(1)(i)). The subpart "does not apply to electrical safety-related work practices for unqualified employees" (§1926.950(a)(1)(ii)). Line-clearance tree trimming done for an organization that operates the lines, and "work involving electric power generation installations," must comply with §1910.269 (§1926.950(a)(3)(i) and (ii)).

Key Concepts

• Single motor, continuous duty: Conductors must have an ampacity of not less than 125 percent of the motor full-load current rating, as determined by 430.6(A)(1) (NEC 430.22).
• Use table FLC, not nameplate: For conductor ampacity, switch ratings, and branch-circuit short-circuit and ground-fault protection, use the values in Tables 430.247–430.250 instead of the nameplate current (430.6(A)(1)). Exceptions: motors built for low speeds (less than 1200 RPM) or high torques, and multispeed motors, use nameplate current. Separate motor overload protection is based on the motor nameplate current rating (430.6(A)(2)).
• Special configurations (conductors between controller and motor): wye-start, delta-run = 72 percent (58% × 1.25) (430.22(C)); part-winding connected = 62.5 percent (50% × 1.25) (430.22(D)); multispeed motor…

Key Concepts

Article 411 — Low-Voltage Lighting - Scope: lighting systems and associated components operating at no more than 30 volts ac or 60 volts dc; where wet contact is likely, the limits are 15 volts ac or 30 volts dc (411.1). - A low-voltage lighting system consists of an isolating power supply, low-voltage luminaires, and associated equipment all identified for the use, and the output circuits of the power supply shall be rated for 25 amperes maximum under all load conditions (411.3). - Listing: systems must comply with 411.4(A) or (B), and listed systems (or systems assembled from listed parts) shall not be reconditioned (411.4). Assembly of listed parts is permitted using low-voltage luminaires identified for the use,…

Key Concepts

Listing, reconditioning, and inspection - All luminaires, lampholders, and retrofit kits shall be listed (410.6). Luminaires, lampholders, and retrofit kits shall not be reconditioned; a retrofit kit installed per its instructions does not make the luminaire "reconditioned" (410.7). - Luminaires must be installed so connections between luminaire conductors and circuit conductors can be inspected without disconnecting wiring, unless connected by attachment plugs and receptacles (410.8). - Luminaires shall have no live parts normally exposed to contact; exception: cleat-type lampholders at least 2.5 m (8 ft) above the floor may have exposed terminals (410.5).

Key Concepts

Transformer / electronic power supply ratings (600.23) - Secondary-circuit current rating: not more than 300 mA — 600.23(D). - Secondary-circuit voltage: not over 15,000 volts nominal under any load; voltage to ground at any secondary output terminal not over 7500 volts — 600.23(C). - Secondary circuit outputs shall not be connected in parallel or in series — 600.23(E). - Secondary-circuit ground-fault protection is required except for transformers with isolated ungrounded secondaries and max open-circuit voltage of 7500 volts or less, and transformers with integral porcelain or glass secondary housing needing no field wiring — 600.23(B). Units equipped with that protection shall be marked — 600.23(F). - Transformers and electronic power supplies shall be identified for the use…

Key Concepts

Construction-site fire alarm and extinguisher rules (OSHA Subpart F) - An alarm system — "e.g., telephone system, siren, etc." — shall be established by the employer so that employees on the site and the local fire department can be alerted for an emergency (1926.150(e)(1)). The alarm code and reporting instructions shall be conspicuously posted at phones and at employee entrances (1926.150(e)(2)). - A fire extinguisher rated not less than 2A shall be provided for each 3,000 square feet of protected building area, or major fraction thereof; travel distance to the nearest extinguisher shall not exceed 100 feet (1926.150(c)(1)(i)). - One or more extinguishers rated not less than 2A on each floor; in multistory buildings at least one…

Key Concepts

Definitions — §1926.32 (OSHA 1926 CFR 29, Page 31) - Competent person (f): "one who is capable of identifying existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them." The definition requires no degree, years of experience, or training certificate. - Qualified (m): one who, by recognized degree, certificate, or professional standing, or by extensive knowledge, training, and experience, has successfully demonstrated the ability to solve or resolve problems relating to the subject matter, the work, or the project. - Authorized person (d): approved or assigned by the employer for a specific duty or location; designated person…

Mississippi Master Electrician | 6 questions, 8% of exam

Key Concepts

Plug fuses, fuseholders, and adapters (NEC 240.50) - Plug fuses are permitted in circuits not exceeding 125 volts between conductors, and in circuits supplied by a system having a grounded neutral point where the line-to-neutral voltage does not exceed 150 volts [240.50(A)]. - Each fuse, fuseholder, and adapter shall be marked with its ampere rating [240.50(B)]. - Plug fuses of 15-ampere and lower rating shall be identified by a hexagonal configuration of the window, cap, or other prominent part to distinguish them from fuses of higher ampere ratings [240.50(C)]. - Plug fuses, fuseholders, and adapters shall have no exposed energized parts after installation [240.50(D)]. The screw shell of…