Tennessee CE Electrical Contractor

Key Concepts

Purpose, scope and arrangement (Article 90) - The purpose of the Code is "the practical safeguarding of persons and property from hazards arising from the use of electricity." It "is not intended as a design specification or an instruction manual for untrained persons" (90.1(A)). - 90.2(A) covers "the installation and removal of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and raceways; and optical fiber cables and raceways" for public and private premises, including buildings, structures, mobile homes, recreational vehicles, and floating buildings. - 90.3: the Code is divided into an introduction and nine chapters; Chapters 1–4 apply generally; Chapters 5, 6, and 7 cover special occupancies, equipment, and conditions; Chapter 8 (communications) is not…

Source: Ugly's Electrical References, "Electrical Symbols," Pages 125–127

Key Concepts

Switch outlet symbols (Page 125). Switch symbols are built on the letter "S" with a subscript identifying the switch type: - S — single-pole switch - S₂ — double-pole switch - S₃ — three-way switch - S₄ — four-way switch - S_D — door switch - S_E — electrolier switch - S_P — switch and pilot lamp - S_K — key-operated switch - S_CB — circuit breaker; S_WCB — weather-proof circuit breaker - S_MC — momentary-contact switch; S_RC — remote-control switch - S_WP — weather-proof switch; S_F — fused switch; S_WPF — weather-proof fused switch

Page 125 also shows the lighting switch and power panel symbols.

Key Concepts

Code arrangement (90.3). The Code is divided into an introduction and nine chapters. Chapters 1, 2, 3, and 4 apply generally. Chapters 5, 6, and 7 apply to special occupancies, special equipment, or other special conditions and may supplement or modify the requirements in Chapters 1 through 7. Chapter 8 covers communications systems and is not subject to the requirements of Chapters 1 through 7 except where specifically referenced in Chapter 8. Chapter 9 consists of tables that are applicable as referenced. Informative annexes are not part of the requirements and are included for informational purposes only (90.5(D)).

Key Concepts

Overcurrent protection of conductors (Article 240) - Small conductors, 240.4(D): 16 AWG copper — max 10 amperes, provided continuous loads do not exceed 8 amperes and proper OCPDs are used [240.4(D)(2)]; 14 AWG copper — max 15 amperes [240.4(D)(3)]; 12 AWG copper — max 20 amperes [240.4(D)(5)]. - 240.4(B): The next higher standard OCPD rating above conductor ampacity is permitted only if all three conditions are met, including that the conductors are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads, and that the next higher standard rating does not exceed 800 amperes. - 240.4(C): Where the OCPD is rated over 800 amperes, conductor ampacity must be **equal to or greater…

Tennessee CE Electrical Contractor — 15 questions (15% of exam)

Key Concepts

Grounded conductor identification (Article 200) - 6 AWG or smaller: continuous white outer finish, continuous gray outer finish, or three continuous white or gray stripes along the entire length on other than green insulation — 200.6(A). - 4 AWG or larger: may be identified at installation by a distinctive white or gray marking at its terminations; the marking shall encircle the conductor or insulation — 200.6(B)(4). - Reidentifying a white/gray conductor in a cable assembly as ungrounded (50 V or more): identification shall encircle the insulation and be a color other than white, gray, or green — 200.7(C)(1). - Terminals for grounded conductors shall be **substantially white…

Key Concepts

Transformers — overcurrent protection (Article 450) - Transformers over 1000 volts: protection per Table 450.3(A) [450.3(A); Page 551]; transformers 1000 volts, nominal, or less: protection per Table 450.3(B) [450.3(B); Page 552]. - Two methods exist for 1000 V or less: primary only protection, or primary and secondary protection. Method 2 requires secondary protection at not more than 125 or 167 percent (depending on secondary current rating), provided primary protection is not more than 250 percent [Table 450.3(B) commentary, Page 552]. - Where secondary protection is required, the secondary device may consist of not more than six circuit breakers or six sets of fuses grouped in one location, and the total of all device ratings shall not exceed…

Key Concepts

• Branch-circuit conductors, single motor, continuous duty: ampacity not less than 125 percent of motor full-load current (FLC) as determined by 430.6(A)(1) — NEC 430.22 (Handbook p. 501).
• Table FLC vs. nameplate: For general motor applications, the values in Tables 430.247–430.250 are used for conductor ampacity, switch ratings, and branch-circuit short-circuit and ground-fault (BCSC/GF) protection, instead of the nameplate current — 430.6(A)(1). Separate motor overload protection is based on the motor nameplate current rating — 430.6(A)(2). Table 430.247 = DC, 430.248 = single-phase AC, 430.249 = two-phase, 430.250 = three-phase.
• Special conductor multipliers (430.22): DC motor from single-phase half-wave rectifier 190%, full-wave rectifier 150% [430.22(A)(1),(2)]; multispeed motor — line side of controller based on the…

Tennessee CE Electrical Contractor

Key Concepts

Article 411 — Low-Voltage Lighting - Article 411 covers lighting systems and components operating at no more than 30 volts ac or 60 volts dc; where wet contact is likely, limits are 15 volts ac or 30 volts dc (411.1). - Output circuits of the power supply shall be rated for 25 amperes maximum under all load conditions (411.3). - Lighting systems shall be installed not less than 3 m (10 ft) horizontally from the nearest edge of the water, unless permitted by Article 680 (411.5(B)). - Secondary circuits shall not be grounded (411.6(A)); the secondary must be insulated from the branch circuit by an isolating transformer (411.6(B)).

Key Concepts

• Class I locations are those in which flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors are or may be present in air in quantities sufficient to produce explosive or ignitible mixtures (Art. 500; Handbook pp. 583–584). Class I, Division 1 = ignitible gas/vapor normally present (500.5(B)(1)).
• Class II locations are hazardous because of combustible dust (500.5(C)), separated into Groups E, F, and G per 500.6(B). Division 1 typically involves a dust cloud present continuously/intermittently under normal operation, or a dust layer likely to exceed 1/8 in. on major horizontal surfaces (Handbook p. 614). Combustible dust is 500 microns or smaller (U.S. No. 35 sieve), per Article 100.
• Class III locations involve ignitible fibers/flyings…

Key Concepts

Electric signs and outline lighting (Article 600)

• Listing: All electric signs, section signs, outline lighting, PV powered signs and retrofit kits must be listed; field-installed skeleton tubing is not required to be listed where installed in conformance with the Code — 600.3(A).
• Sign outlet: Each commercial building and each commercial occupancy accessible to pedestrians must have at least one outlet at each entrance to each tenant space for sign or outline lighting use, supplied by a branch circuit rated at least 20 amperes that supplies no other load. Service hallways or corridors are not considered accessible to pedestrians — 600.5(A).
• Circuit ratings: Sign branch circuits are continuous loads for calculation purposes; **neon tubing installations…

Tennessee CE Electrical Contractor

Key Concepts

Classification of locations - Class II locations are "those that are hazardous because of the presence of combustible dust" — NEC 500.5(C). Subdivided into Division 1 and Division 2 by the likelihood combustible dust is present in hazardous quantities. - Class III locations are hazardous because of easily ignitible fibers or materials producing combustible flyings that are handled, manufactured, or used, but are not likely to be in suspension in air in ignitible quantities — NEC 500.5(D); Article 503.1 scope covers Class III, Division 1 and 2 where fire or explosion hazard may exist due to ignitible fibers/flyings. Typical: textile mills, woodworking plants (503.1 commentary). - Group E dusts (containing magnesium or aluminum)…

Key Concepts

Definitions (29 CFR 1926.32, Page 31) - Competent person — §1926.32(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." - Qualified — §1926.32(m): one who, by recognized degree, certificate, or professional standing, or by extensive knowledge, training, and experience, has successfully demonstrated ability to solve or resolve problems relating to the subject matter, work, or project. - Qualified Person (Ugly's, Page 177, NFPA 70E): one who has demonstrated skills and knowledge related to the construction and operation of electrical equipment and installations and has received safety training to identify…