Maryland Journeyperson Electrician

Key Concepts

Ohm's Law is the backbone of this section. It defines the relationship between voltage (E or V), current (I), and resistance (R): - E = I × R | I = E / R | R = E / I

Power (Watt's Law): - P = E × I | P = I² × R | P = E² / R

Key Definitions to Know: - Voltage (EMF): Electrical pressure that drives current through a circuit (measured in Volts) - Current: Flow of electrons through a conductor (measured in Amperes) - Resistance: Opposition to current flow (measured in Ohms, Ω) - Impedance (Z): Total opposition to current in an AC circuit, including resistance and reactance (measured in Ohms) - Inductance: Property of a conductor that opposes changes in current (measured in Henrys) - Capacitance: Ability to store electrical charge (measured in Farads) - Power Factor (PF): Ratio of true power (watts) to apparent power (VA); PF = kW / kVA

Key Concepts

Article 100 — Definitions Know these cold — they appear in questions across every subtopic: - Ampacity: Max current a conductor can carry continuously under conditions of use without exceeding its temperature rating. - Branch Circuit types: General-purpose (2+ outlets), Appliance (outlets only, no permanent luminaires), Individual (one utilization equipment), Multiwire (2+ ungrounded conductors with a grounded conductor at equal voltage to each). - AFCI: Protects against arc faults by recognizing arcing characteristics and de-energizing the circuit. - Bonding vs. Grounding: Bonding = electrical continuity between metal parts. Grounding = intentional connection to earth. These are NOT interchangeable. - AHJ: Authority Having Jurisdiction — approves equipment, installations, and procedures.

Article 110 — Requirements for Electrical Installations - Working space (110.26): 36 inches deep minimum in front of electrical equipment up to 150V to ground; increases with voltage. 6.5 ft minimum headroom. Width must be at least the width of the equipment or 30 inches, whichever is greater. - Conductor terminations at 75°C rating unless equipment is marked otherwise. - Unused openings in enclosures must be closed.

Key Concepts

Article 300 — General Requirements - All conductors of the same circuit (including grounded and EGC) must be contained in the same raceway, cable, or cord (300.3(B)). This prevents inductive heating from split-phase currents. - Single conductors (Table 310.4(A)) can only be installed as part of a recognized wiring method — not run alone unless permitted (e.g., overhead per 225.6). - AC and DC circuits rated 1000V or less can share the same raceway, but all conductors must be insulated for the highest voltage present (300.3(C)(1)). - Wiring methods in Chapter 3 apply to systems 1000V or less unless a specific section permits higher voltage (300.2(A)). - Physical protection rules (300.4): When cables run within 32mm (1¼ in.) of the edge of a framing member, a steel plate at least 1.6mm (1/16 in.) thick is required. Exceptions: RMC, IMC, RNC, and EMT do not require steel plate protection. - NM cable through metal framing holes requires listed bushings or grommets over all metal edges (300.4(B)(1)).

Key Concepts

Article 400 – Flexible Cords and Flexible Cables - Flexible cords must be suitable for conditions of use and location (400.3). Type and application are governed by Table 400.4. - Ampacities are found in Tables 400.5(A)(1) and 400.5(A)(2) for up to 3 current-carrying conductors. When more than 3 current-carrying conductors are present, apply derating factors from Table 400.5(A)(3). - A neutral carrying only unbalanced current is NOT a current-carrying conductor. However, on a 4-wire, 3-phase wye circuit where more than 50% of the load is nonlinear, the neutral is a current-carrying conductor. - Equipment grounding conductors are never counted as current-carrying conductors. - Standard flexible cord types (S, SJ, SO, ST, etc.) must be surface-marked every 24 inches (610 mm) with type, size, conductor count, and maximum operating temperature.

Article 422 – Appliances - Appliances must be installed per their listing and the NEC. Branch-circuit sizing depends on whether the appliance is motor-operated, resistance-heating, or a combination. - Cord-and-plug-connected appliances must have the cord visible for its entire length and not run through walls, ceilings, or floors.

Key Concepts

Hazardous (Classified) Locations – Articles 500–504

Classification by Class, Division, and Group is the foundation of Article 500.

• Class I – Flammable gases, vapors, or flammable/combustible liquid-produced vapors (Article 501)
• Class II – Combustible dusts (Article 502)
• Class III – Ignitible fibers/flyings (Article 503)

Divisions define the likelihood of hazard being present: - Division 1 – Hazard exists under normal operating conditions - Division 2 – Hazard present only under abnormal conditions (failure, accident)

Documentation (500.4): All hazardous locations must be documented and that documentation must be available to those who design, install, inspect, maintain, or operate equipment at the location.

Article 500.3: All other applicable NEC rules still apply in hazardous locations except as modified by Articles 500–504.

Class I, Division 1 Wiring (501.10): - All boxes and fittings must be approved for Class I, Division 1 - Flexible connections at motor terminals are permitted using: listed flexible fittings, flexible cord per 501.140 with listed cord connectors, or listed Type TCER-HL cable in industrial settings with restricted public access

NEC Articles 600–695 | 2 Questions, ~3% of Exam

Key Concepts

Article 600 — Electric Signs and Outline Lighting

• Listing required (600.3): All fixed, mobile, or portable electric signs, retrofit kits, and outline lighting must be listed and labeled, regardless of voltage. Two exceptions: field-installed skeleton tubing and outline lighting using listed luminaires wired per Chapter 3 do not require system-level listing.
• Markings (600.4): Signs must show manufacturer's name, input voltage, and current rating. Signs with incandescent lampholders must be permanently marked with max wattage per lampholder in letters at least 6 mm (¼ in.) high, visible during relamping.
• Retrofit kits: Modified signs must be marked indicating the illumination system was replaced, including the kit provider's and installer's identifier. LED retrofit signs using existing sockets require a warning label per 110.21(B) that fluorescent lamps must not be reinstalled.
• Disconnect (600.6): A disconnect is required within sight of the sign, or capable of being locked in the open position. Signs in occupancies with neon tubing require the disconnect to allow safe servicing.

Maryland Journeyperson Electrician Exam — NEC Articles 700–830 (9% of Exam)

Key Concepts

Article 700 — Emergency Systems

• Emergency power must be available within 10 seconds of normal supply failure (700.12).
• Storage batteries must supply the total load for a minimum of 1½ hours without voltage dropping below 87½% of normal. Automotive-type batteries are prohibited (700.12(C)).
• Internal combustion engine generators must have an on-site fuel supply sufficient for not less than 2 hours of operation (700.12(D)(2)(a)).
• Prime movers cannot be solely dependent on a public utility gas system or municipal water supply (700.12(D)(2)(c)).
• Generator control wiring between transfer equipment and the emergency generator must be entirely independent of all other wiring. Loss of integrity of the remote start circuit shall start the generator (700.10(D)(4)).

Feeder-Circuit Wiring Protection (700.10(D)(2)) — Must meet one of: 1. Installed in spaces with approved automatic fire protection 2. Protected by a listed electrical circuit protective system with 2-hour fire rating 3. Listed fire-resistive cable system with 2-hour fire rating 4. Listed fire-rated assembly with 2-hour fire rating containing only emergency circuits 5. Encased in a minimum of 50 mm (2 in.) of concrete