Idaho Limited Electrical Photovoltaic Installer

Exam topic: 2017 National Electrical Code, NFPA – Introduction (Article 90)

Key Concepts

Purpose (90.1) - 90.1(A): The purpose of the Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. It is not a design specification or an instruction manual for untrained persons. - 90.1(B) Adequacy: Compliance plus proper maintenance results 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. - 90.1(C): Code requirements address the fundamental principles of protection for safety in Section 131 of IEC 60364-1, Electrical Installations of Buildings.

Key Concepts

Article 100 definitions (the highest-value memorization). - Ampacity — the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating (NEC 2017, Page 9, Article 100). - Continuous Load — a load where the maximum current is expected to continue for 3 hours or more (Article 100, Page 8). - Authority Having Jurisdiction (AHJ) — an organization, office, or individual responsible for enforcing a code or standard, or for approving equipment, materials, an installation, or a procedure (Article 100). - Conductor, Insulated — a conductor encased within material of composition and thickness recognized by the Code as electrical insulation; a covered conductor's encasement is not recognized as insulation (Article 100). - Bonding Jumper, Main — the connection between the grounded circuit conductor and the equipment grounding conductor…

Key Concepts

Overcurrent protection (Article 240) - Small-conductor limits, 240.4(D): 18 AWG Cu — 7 A (with conditions); 16 AWG Cu — 10 A (with conditions); 14 AWG Cu — 15 A [240.4(D)(3)]; 12 AWG Al/CCA — 15 A; 12 AWG Cu — 20 A; 10 AWG Al/CCA — 25 A; 10 AWG Cu — 30 A. - 240.4(B): the next higher standard OCPD rating above conductor ampacity is permitted only if all three conditions are met, including that the next higher standard rating selected does not exceed 800 amperes, and the conductors are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads. - 240.4(C): where the device is rated over 800 amperes, conductor ampacity shall be equal to or greater than the device rating per 240.6. - 240.4(F): single-phase (other than 2-wire)…

Key Concepts

Raceway bends, size, securing and support

• Bends in one run: There shall not be more than the equivalent of four quarter bends (360 degrees total) between pull points, for example, conduit bodies and boxes — RMC 344.26, IMC 342.26, PVC 352.26, FMC 348.26, LFMC 350.26, EMT 358.26.
• RMC size: RMC smaller than metric designator 16 (trade size ½) shall not be used (344.20(A)); RMC larger than metric designator 155 (trade size 6) shall not be used (344.20(B)).
• RMC/IMC support: Supported at intervals not exceeding 3 m (10 ft), or per Table 344.30(B)(2) for straight runs made up with threaded couplings — ½–¾ = 10 ft; trade size 1 (metric 27) = 3.7 m (12 ft); 1¼–1½ = 14 ft; 2–2½ = 16 ft; 3 and larger = 20 ft (344.30(B), 342.30(B)(2)). Both must be…

Key Concepts

Transformer overcurrent protection (450.3, 450.4) - Transformers 1000 V or less are protected per Table 450.3(B); over 1000 V per Table 450.3(A) [450.3(A), (B)]. - Table 450.3(B), primary only protection: currents of 9 A or more — not more than 125%; currents less than 9 A — 167%; currents less than 2 A — 300%; no secondary protection required. - Table 450.3(B), primary and secondary protection: primary not more than 250%, secondary 125% for currents of 9 A or more (167% for currents less than 9 A). - Autotransformers 1000 V or less: an individual overcurrent device in series with each ungrounded input conductor, rated or set at not more than 125% of rated full-load input current. Exception: where rated input current is less than 9 A, not more than 167% [450.4(A)]. - Grounding autotransformers: overcurrent protection…

Key Concepts

Classification of locations - Class I locations are those in which 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 II covers combustible dust [502.1]; Class III covers ignitible fibers/flyings [503.1]. - Article 505 is the zone system (Class I, Zone 0, 1, 2) as an alternative to divisions for flammable gases, vapors, or liquids [505.1]. Article 506 is the zone system (Zone 20, 21, 22) for combustible dusts or ignitible fibers/flyings [506.1]. - Zone material groups [506.6]: Group IIIC = conductive combustible dusts; Group IIIB = non-conductive combustible dusts; Group IIIA = ignitible fibers and flyings. - Protection-technique suffixes: Intrinsic safety is designated "ia" for Zone 0, "ib" for Zone 1, "ic" for Zone 2 [505.8(D); 505.2…

Key Concepts

Definitions (690.2). A photovoltaic source circuit is the circuits between modules and from modules to the common connection point(s) of the dc system. A DC-to-DC converter is installed in the PV source or PV output circuit and provides an output dc voltage and current at a higher or lower value than the input. A functional grounded PV system has an electrical reference to ground that is not solidly grounded. A solar cell is the basic PV device that generates electricity when exposed to light. Generating Capacity is the sum of the parallel-connected inverter rated maximum continuous output power at 40°C in kW (690.2; 691.2).

Key Concepts

Article 705 — Interconnected sources - Scope: Article 705 covers installation of one or more electric power production sources operating in parallel with a primary source(s) of electricity (705.1). - Equipment approval: All equipment shall be approved for the intended use; interactive inverters, engine generators, energy storage equipment and wind turbines intended to operate in parallel shall be listed and/or field labeled for interconnection service (705.6). Installation shall be performed only by qualified persons (705.8). - Output characteristics: Output of a generator or other power production source operating in parallel shall be compatible with the voltage, wave shape, and frequency of the system it connects to (705.14). - Disconnecting means, sources: Means shall be provided to disconnect all ungrounded conductors of an electric power production source from all other conductors (705.20) — this is the back-feed protection…

Key Concepts

Table 1 — Percent of cross section for conductors and cables. The permitted fill depends only on the number of conductors/cables in the raceway (NEC 2017, Chapter 9, Table 1): - 1 conductor — 53% - 2 conductors — 31% - Over 2 conductors — 40%

The two-conductor case permits the smallest percentage of the raceway's cross-sectional area. For a raceway containing conductors of different sizes or different insulation types (more than 2 wires), use the 40% column (NEC 2017, Chapter 9, Table 1).

Note (3) — count everything. Equipment grounding or bonding conductors, where installed, shall be included when calculating conduit or tubing fill, and the actual dimensions of the equipment grounding or bonding conductor (insulated or bare) shall be used (Notes to Tables, Note 3; the practice item cites "NEC 2017, Chapter 9, Notes to…

Key Concepts

• Motor current values come from the tables, not the nameplate. For general motor applications, the values in Table 430.247 through Table 430.250 shall be used to determine conductor ampacity and the ampere ratings of switches and branch-circuit short-circuit and ground-fault protection, instead of the actual current marked on the motor nameplate (430.6(A)(1)). Separate motor overload protection, however, is based on the motor nameplate current rating (430.6(A)(2)).
• Single motor conductors: conductors supplying a single motor used 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) (430.22, 430.22(A)).
• Wye-start, delta-run: line-side conductors not less than 125 percent; conductors between the controller and the motor not less than 72 percent of full-load current (430.22(C)). Part-winding: controller-to-motor conductors not less than **62.5…