Maryland Master Electrician

Key Concepts

Article 100 definitions (NEC 2020, Article 100 — Definitions)

• Ampacity — the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.
• Accessible, Readily — capable of being reached quickly for operation, renewal, or inspections without using tools (other than keys), climbing over or under, removing obstacles, or resorting to portable ladders. The Informational Note confirms use of keys is a common alternative under controlled or supervised conditions.
• In Sight From (Within Sight) — the equipment must be visible AND not more than 15 m (50 ft) distant. Both conditions must be met.
• Conductor, Covered vs. Insulated — covered = encased in material of composition or thickness not recognized by the Code as electrical insulation; insulated = material that is recognized as electrical insulation.
• Copper-Clad Aluminum Conductors — copper metallurgically bonded to an aluminum core, with copper forming a minimum of 10 percent of the cross-sectional area of a solid conductor or each strand.
• **GFCI, Class…

Key Concepts

Article 100 — Definitions - Overcurrent: any current in excess of the rated current of equipment or the ampacity of a conductor; may result from overload, short circuit, or ground fault (Art. 100). - Interrupting Rating: the highest current at rated voltage that a device is identified to interrupt under standard test conditions (Art. 100). - Fault Current: the current delivered at a point on the system during a short-circuit condition (Art. 100).

Article 110 - Equipment intended to interrupt current at fault levels must have an interrupting rating at nominal circuit voltage at least equal to the current available at the line terminals of the equipment (110.9). - On a 4-wire, delta-connected system with the midpoint of one phase winding grounded, only the conductor/busbar with the higher phase voltage to ground is marked orange or by other effective means (110.15). - Service equipment at other than dwelling units: field-mark the available fault current, the date of the calculation, and make it durable for the environment (110.24(A)). - Working space width in…

Maryland Master Electrician | 13 questions (14% of exam)

Key Concepts

Article 300 — General requirements - Single conductors are installed only as part of a recognized wiring method of Chapter 3 — 300.3(A). - AC and DC circuits 1000 volts, nominal, or less may share an enclosure, cable, or raceway if all conductors have an insulation rating at least equal to the maximum circuit voltage applied to any conductor in it — 300.3(C)(1). Excitation, control, relay, and ammeter conductors for an individual motor or starter may share the motor-circuit enclosure — 300.3(C)(2)(b). - Neutrals of circuits supplied from a column-width panelboard may originate in the pull box where an auxiliary gutter runs between them and the pull box includes neutral terminations — 300.3(B)(4). Single-conductor Type MI with a nonmagnetic sheath complies with 332.31 — 300.3(B)(3). - Physical protection: bored holes — edge not less than 32 mm (1¼ in.) from the nearest edge of the wood member, else a steel plate at least 1.6 mm (1/16 in.) thick — 300.4(A)(1); parallel to framing…

NEC 2020, Articles 400–411, 422–427, 430–450, 455–490

Key Concepts

Flexible cords and switches (400–411) - Where current-carrying conductors in a flexible cord or cable exceed three, ampacity is reduced: 7 to 9 conductors → 70 percent of the Table 400.5(A)(1) and 400.5(A)(2) values — Table 400.5(A)(3). - Switches and circuit breakers used as switches: 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). - Knife switches over 1200 amperes at 250 volts or less, and over 1000 amperes at 251 to 1000 volts, are used only as isolating switches and shall not be opened under load — 404.13(A). - Snap switches directly connected to aluminum conductors and rated 20 amperes or less shall be marked CO/ALR — 404.14(C). - Where a panelboard is supplied through a transformer, the required overcurrent protection shall be located on the secondary side; an exception permits primary-side protection only where it complies with 240.21(C)(1) — 408.36(B). - Clothes closets:…

Note: the verified questions and reference material for this topic come entirely from NEC 2020 Articles 500–506 (hazardous classified locations). Build your study around that material.

Key Concepts

Location classification (500.5) - Class I — flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors present in air in quantities sufficient to produce explosive or ignitible mixtures [500.5(B)]. - Class II — hazardous because of the presence of combustible dust [500.5(C)]. A Class II, Division 1 location includes one in which Group E combustible dusts may be present in quantities sufficient to be hazardous in normal or abnormal operating conditions [500.5(C)(1)(3)]. - Class III — hazardous because of easily ignitible fibers or where materials producing combustible flyings are handled, manufactured, or used, but in which such fibers/flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitible mixtures [500.5(D)]. - An area adjacent to a Class I, Division 1 location is Division 2 where ignitible concentrations might occasionally be communicated, unless prevented by adequate positive-pressure ventilation from a source…

Key Concepts

Signs and outline lighting (Article 600)

• Required sign outlet: Each commercial building and each commercial occupancy accessible to pedestrians shall have at least one outlet in an accessible location at each entrance to each tenant space, supplied by a branch circuit rated at least 20 amperes that supplies no other load — 600.5(A). Not required at entrances for deliveries, service corridors, or service hallways used only by service personnel or employees.
• Branch-circuit ratings: Neon tubing installations — not rated in excess of 30 amperes — 600.5(C)(1); all other signs and outline lighting — rated not to exceed 20 amperes — 600.5(C)(2). Sign branch circuits are continuous loads.
• Control switch rating: Switches, flashers, and similar devices controlling transformers and electronic power supplies shall be rated for controlling inductive loads or have a current rating not less than twice the current rating of the transformer or electronic power supply — 600.6(B).
• Transformers/electronic power supplies: Secondary-circuit voltage shall not exceed 15,000 volts, nominal, under any load condition, and voltage to ground…

Key Concepts

Emergency systems (Article 700) - Emergency lighting, emergency power, or both shall be available within the time required for the application but not to exceed 10 seconds after failure of the normal supply (700.12). Generator sets requiring more than 10 seconds to develop power are permitted if an auxiliary power supply energizes the emergency system until the generator picks up the load (700.12(D)(4)). - Where internal combustion engines are the prime mover, an on-site fuel supply shall be sufficient for not less than 2 hours' operation (700.12(D)(2)(a)). Fuel cell systems (700.12(G)) and dc microgrid systems (700.12(H)) must supply the total load for not less than 2 hours of full-demand operation. - Fire protection applies in these occupancies: assembly occupancies for not less than 1000 persons; buildings above 23 m (75 ft) in height; educational occupancies with more than 300 occupants (700.10(D)(1)). - Feeder-circuit wiring must meet one of: in spaces fully protected by an approved automatic fire protection system; a listed electrical circuit protective system with a minimum 2-hour fire rating; a…

Key Concepts

Dwelling service sizing. For a 120/240-volt, single-phase service supplying the entire load of a one-family dwelling, 310.12(A) (310.15(B)(7) in NEC 2017) permits service conductors with an ampacity of not less than 83 percent of the service rating; Table 310.12(A) lists the sizes directly. Standard overcurrent ratings come from 240.6(A), and where a calculated load falls between standard ratings, the next higher standard size is used (as in Annex D, Example D3).

Continuous loads. Feeder minimum ampacity = noncontinuous + 125% of continuous (215.2(A)(1)(a) in NEC 2020; 215.4(A)(1) in NEC 2026). The same rule applies to service-entrance conductors per 230.42(A)(1).

Non-dwelling loads. Unit lighting loads come from Table 220.12 (NEC 2020); retail is 1.9 VA/ft². Receptacle outlets are calculated at not less than 180 VA for each single or multiple receptacle on one yoke (220.14(I)). Demand factors: Table 220.44 (non-dwelling receptacles, first 10 kVA at 100%, remainder at 50%); Table 220.56 (kitchen equipment, 6 and over = 65%, but never less than the sum of the largest two loads).