Tennessee LLE Limited Licensed Electrician

Key Concepts

Approval and listing (NEC Article 110, Part I) - Conductors and equipment required or permitted by the Code "shall be acceptable only if approved" (110.2). "Approved" is defined in Article 100 as "Acceptable to the authority having jurisdiction." - The AHJ is "an organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure" (Article 100). - Listed or labeled equipment "shall be installed and used in accordance with any instructions included in the listing or labeling" (110.3(B)). Judging equipment considers suitability, mechanical strength, wire-bending and connection space, insulation, heating effects, arcing effects, and classification (110.3(A)). - Reconditioned equipment must be marked with the name, trademark, or other descriptive marking identifying the reconditioning organization, along with the date of reconditioning, and identified as "reconditioned"…

Tennessee | NEC 2017

Key Concepts

Working space (NEC 110.26, Part II — 1000 Volts, Nominal, or Less) - Depth must not be less than Table 110.26(A)(1), measured from exposed live parts, or from the enclosure/opening if live parts are enclosed [110.26(A)(1)]. Conditions: 1 = live parts one side, no live or grounded parts opposite (or both sides guarded by insulating materials); 2 = live parts one side, grounded parts opposite — concrete, brick, or tile walls are considered grounded; 3 = exposed live parts both sides. - Width = width of the equipment or 762 mm (30 in.), whichever is greater, and must permit at least a 90-degree opening of doors or hinged panels [110.26(A)(2)]. - Height = clear from grade/floor/platform to 2.0 m (6½ ft) or the height of the equipment, whichever is greater; associated equipment above…

NEC 2017

Key Concepts

Number and routing of services (Art. 230, Part I) - A building or structure shall be supplied by only one service unless permitted in 230.2(A) through (D) — 230.2. - Additional services are permitted for special conditions: fire pumps, emergency systems, legally required standby, optional standby, parallel power production, and systems for multiple sources for enhanced reliability — 230.2(A)(1) through (6). - Additional services are permitted where capacity requirements are in excess of 2000 amperes at a supply voltage of 1000 volts or less — 230.2(C)(1). - Service conductors supplying a building or other structure shall not pass through the interior of another building or other structure — 230.3. - Conductors are considered outside a building when installed under not less than 2 in. (50 mm) of concrete beneath the building, in a raceway encased…

Key Concepts

• Scope of Article 240. Parts I through VII give general requirements for overcurrent protection and overcurrent protective devices not more than 1000 volts, nominal; Part VIII covers supervised industrial installations at not more than 1000 volts, nominal; Part IX covers over 1000 volts, nominal. (NEC 2017, 240.1)
• Supervised industrial installation (for Part VIII) requires all of: qualified persons monitor and service the system; the premises wiring system has 2500 kVA or greater of load used in industrial process(es), manufacturing activities, or both, calculated per Article 220; and at least one service or feeder more than 150 volts to ground and more than 300 volts phase-to-phase. Offices, warehouses, garages, machine shops and recreational facilities not integral to the plant are excluded. (240.2)
• Conductor protection. Conductors, other than flexible cords, flexible cables, and fixture wires, are…

Key Concepts

• Purpose of system grounding — Grounded systems shall be connected to earth in a manner that limits the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and stabilizes the voltage to earth during normal operation (250.4(A)(1)).
• Earth is never a fault path — The earth shall not be considered an effective ground-fault current path for grounded systems (250.4(A)(5)) or an effective fault-current path for ungrounded systems (250.4(B)(4)).
• Objectionable current — Grounding shall be installed and arranged to prevent objectionable current (250.6(A)). Temporary currents from abnormal conditions, such as ground faults, are not classified as objectionable (250.6(C)).
• Connections — Permitted: listed pressure connectors, terminal bars, pressure connectors listed as grounding and bonding equipment, exothermic welding, machine screws engaging not less than two threads, listed assemblies, other listed means (250.8(A)). **Connection…

Key Concepts

• Parallel conductors. Aluminum, copper-clad aluminum, or copper conductors for each phase, polarity, neutral, or grounded circuit may be connected in parallel (joined at both ends) only in sizes 1/0 AWG and larger [NEC 2017, 310.10(H)(1)]. Paralleled conductors must be the same length, same material, same circular mil size, same insulation type, and terminated in the same manner [310.10(H)(2)].
• Wet-location insulations. Types listed for wet locations include MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THWN, THWN-2, XHHW, XHHW-2, and ZW [310.10(C)]. THHN is rated dry and damp only.
• Over 2000 volts. Solid dielectric insulated conductors operated above 2000 volts in permanent installations shall have ozone-resistant insulation and shall be shielded [310.10(E)].
• Ampacity baseline. Table 310.15(B)(16) is based on an ambient temperature of 30°C (86°F); correction factors apply where the ambient is other than 30°C…

Based on NEC 2017 (Tennessee)

Key Concepts

Securing and supporting intervals (memorize by raceway type):

• EMT (358.30(A)): securely fastened at intervals not to exceed 3 m (10 ft), and each run securely fastened within 900 mm (3 ft) of each outlet box, junction box, device box, cabinet, conduit body, or other tubing termination. Exception No. 1 allows fastening of unbroken lengths to increase to 1.5 m (5 ft) where structural members do not readily permit fastening within 3 ft.
• PVC (352.30(A)): securely fastened within 900 mm (3 ft) of each outlet box, junction box, device box, conduit body, or other conduit termination. Supports per Table 352.30.
• FMC (348.30(A)) and LFMC (350.30(A)): securely fastened within 300 mm (12 in.) of each box, cabinet, conduit body, or other conduit termination, and supported/secured at intervals **not to exceed 1.4…

Key Concepts

Classification (Article 500) - "Class II locations are those that are hazardous because of the presence of combustible dust" — 500.5(C). Class II is subdivided into Division 1 and Division 2. - Class III locations are hazardous because of easily ignitible fibers or materials producing combustible flyings not likely to be in suspension in ignitible quantities — 500.5(D). Unlike Class I (Groups A, B, C, D) and Class II (Groups E, F, G), Class III has no material group designations — 500.6. - Informational Note to 500.5(C)(1): "Dusts containing magnesium or aluminum are particularly hazardous" (Group E), requiring extreme precaution. - Refrigerant machinery rooms with ammonia refrigeration may be unclassified where adequate mechanical ventilation operates continuously or is initiated by detection at a concentration not exceeding 150 ppm — 500.5(A).

Key Concepts

Overhead separations — communications and coax (Art. 800/820/840). - Where communications wires/cables share a pole with electric light or power conductors, where practicable the communications wires and cables shall be located below the power conductors — 800.44(A)(1). Same rule for coax, 820.44(A)(1), and for outside plant optical fiber, 840.44(A)(1). - Communications wires/cables shall not be attached to a cross-arm carrying light or power conductors — 800.44(A)(2); 820.44(A)(2). Climbing space must comply with 225.14(D) — 800.44(A)(3). - Supply service drops of 0 to 750 volts above and parallel to communications service drops: minimum separation 300 mm (12 in.) at any point in the span, including at the building attachment, with not less than 1.0 m (40 in.) at the pole — 800.44(A)(4); same 12 in./40 in. pair in 840.44(A)(4) and 770.44(A)(4). - Coax lead-in/overhead-drop cables must be kept…

Key Concepts

Electric signs and outline lighting (Article 600)

• A disconnect located at the point of entry shall open all ungrounded conductors where the feeder/branch circuit enters the enclosure of the sign or pole — NEC 2017, 600.6(A)(1). Each sign, outline lighting system, feeder or branch circuit shall be controlled by an externally operable switch or circuit breaker that opens all ungrounded conductors and controls no other load (600.6). Exceptions: no disconnect required for an exit directional sign inside a building, or for cord-connected signs with an attachment plug.
• Branch-circuit ratings: neon tubing installations — not in excess of 30 amperes (600.5(B)(1)); all other signs and outline lighting systems — not to exceed 20 amperes (600.5(B)(2)). Sign circuits are considered continuous loads. The required sign outlet is supplied by a branch circuit rated at least 20 amperes…