South Carolina Electrician

Key Concepts

Ohm's Law & DC Circuits The foundation of all circuit calculations. V = IR, where voltage (V) is in volts, current (I) is in amperes, and resistance (R) is in ohms. Power: P = VI = I²R = V²/R. In series circuits, resistance adds directly. In parallel circuits, total resistance is found by reciprocal sum (1/R_total = 1/R1 + 1/R2 + ...).

AC Circuit Theory - Impedance (Z): Total opposition to AC current; Z = √(R² + X²), measured in ohms - Inductive Reactance: X_L = 2πfL (opposes increases in current; voltage leads current by 90°) - Capacitive Reactance: X_C = 1/(2πfC) (voltage lags current by 90°) - Power Factor (PF): PF = cos θ = True…

Key Concepts

Branch Circuit Ratings & Voltage Limitations (Article 210) - Standard branch circuit ratings: 15, 20, 30, 40, and 50 amperes - Receptacle loads must not exceed 80% of branch circuit rating for continuous loads - Maximum voltage for residential branch circuits: 120V for luminaires and receptacles in dwelling units; 240V permitted for fixed appliances - A single receptacle on an individual branch circuit must be rated equal to the circuit ampacity

GFCI Protection Requirements (210.8) - Required in: bathrooms, garages, outdoors, crawl spaces, unfinished basements, kitchens (within 6 ft of sink), boathouses, swimming pool areas, rooftops, and all 15/20A 125V receptacles in dwelling units (2020 NEC expanded scope) - AFCI protection (210.12) required for ALL 120V,…

9 questions | 11% of exam | NEC 2020 Reference

Key Concepts

Grounding Electrode System (NEC Article 250, Part III)

• The grounding electrode system must use all available electrodes at a structure: metal underground water pipe (≥10 ft in contact with earth), metal building frame, concrete-encased electrode (Ufer ground — ≥20 ft of ½" rebar or #4 AWG bare copper in concrete), ground ring, rod/pipe/plate electrodes, and other listed electrodes (250.52).
• Concrete-encased electrode is required when a new concrete foundation is poured — it cannot be omitted (250.50).
• A single rod, pipe, or plate electrode must have a resistance to earth ≤25 ohms OR be supplemented by an additional electrode (250.56).
• **Prohibited electrodes…

Key Concepts

Conductor Insulation Types & Temperature Ratings

Know these common insulation types cold: - THHN: 90°C dry locations only — most common in conduit - THWN / THWN-2: 75°C wet, 90°C dry (THWN-2 = 90°C wet/dry) - XHHW: 90°C dry, 75°C wet (cross-linked polyethylene) - XHHW-2: 90°C wet and dry - RHW: 75°C wet/dry, rubber insulation - USE: Underground service entrance, 75°C, suitable for direct burial - UF (Underground Feeder): 60°C, suitable for direct burial and damp/wet locations; factory assembly only - TW: 60°C wet/dry — lowest rating, often a distractor

Even though THHN is rated 90°C, ampacity is typically derated to 75°C when terminating at equipment with 75°C-rated terminals (NEC 110.14(C)).

(9 questions, 11% of exam — NEC 2020)

Key Concepts

Conduit Fill (Chapter 9, Table 1 & Annex C) - 1 conductor: 53% fill; 2 conductors: 31% fill; 3+ conductors: 40% fill - Use Annex C tables to find maximum conductor count by conduit type and size — don't recalculate when the table gives you the answer directly

Box Fill Calculations (Article 314) - Each ungrounded conductor = 1 volume allowance based on largest conductor in box - Each grounded conductor = 1 allowance; all EGCs together = 1 allowance total - Each device (switch/receptacle) = 2 allowances; each internal clamp = 1 allowance; each luminaire stud/hickey = 1 allowance - Volume per conductor size: #14 = 2.00…

Key Concepts

Hazardous Location Classification (Article 500)

Class I — Flammable gases or vapors (e.g., gasoline, hydrogen) Class II — Combustible dusts (e.g., grain, coal, metal dust) Class III — Ignitible fibers/flyings (e.g., textile mills, sawmills)

Division 1 — Hazardous conditions exist under normal operations Division 2 — Hazardous conditions exist only under abnormal conditions (failure, accident)

Zone system (Article 505/506) provides an alternative to Division classification: - Zone 0 = continuous hazard (equivalent to most severe Div. 1) - Zone 1 = likely during normal ops - Zone 2 = not likely during normal ops (equivalent to Div. 2)

Key Concepts

Overcurrent Protection (NEC Article 240)

• Fuses and circuit breakers must be rated to protect the conductor, not just the load.
• Standard fuse/breaker sizes: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400A (NEC 240.6).
• Next-size-up rule (NEC 240.4(B)): If calculated ampacity doesn't match a standard size, you may use the next larger standard OCPD — but only for conductors 800A or less, and only if not already protected by a smaller device.
• Circuit breakers must open all ungrounded conductors simultaneously on multi-wire circuits.

Article 430 (and Article 440 for hermetic compressors) | 7 questions, 9% of exam

Key Concepts

Branch-Circuit Conductor Sizing (430.22) Size conductors at 125% of the motor's full-load current (FLC). Use Table values (430.247–430.250) — NOT the nameplate current — for general motor applications (430.6(A)(1)). Exception: use nameplate FLA for low-speed (<1200 RPM), high-torque, or multispeed motors.

Motor Overload Protection (430.32) - Motors with a marked service factor ≥ 1.15 or marked temperature rise ≤ 40°C: set at 125% of FLC - All other motors: set at 115% of FLC - If the overload device won't allow the motor to start, you may increase up to 140% (SF ≥ 1.15 or ≤ 40°C rise) or 130% (all others)…

Key Concepts

Class 1, 2, and 3 Circuit Classifications (Article 725) - Class 1: Power-limited circuits operating at ≤30V/1000VA, or non-power-limited circuits up to 600V. Class 1 wiring methods follow standard Chapter 3 rules. - Class 2: Power-limited, ≤100VA at ≤30V (or ≤150VA at higher voltages per source limits). Lowest hazard — least restrictive wiring rules after leaving the power supply. - Class 3: Power-limited with higher voltage/power limits than Class 2 (up to 100V). Requires insulation suitable for higher voltage. Conductors must be insulated for the voltage involved. - Cable types: CL2 and CL3 for general use; CL2P/CL3P for plenum; CL2R/CL3R for riser; PLTC (Power-Limited Tray Cable) for cable trays.

(NEC 2020 | Article 410 core; also 210.6, 410.10, 410.16, 410.36, 410.44, 410.62, 410.116, 410.130)

Key Concepts

Luminaire Location Requirements (NEC 410.10)

• Wet locations: Luminaires must be listed and marked "Suitable for Wet Locations."
• Damp locations: Luminaires must be listed and marked "Suitable for Damp Locations" (wet-rated fixtures are also acceptable).
• Corrosive locations: Must use fixtures specifically listed for corrosive environments.
• Bathrooms: Luminaires within a bathtub/shower zone (3 ft horizontal, 8 ft vertical from the top of the tub or shower threshold) must be listed for damp or wet locations as applicable.
• Clothes closets: Only listed surface-mounted or recessed incandescent/LED fixtures with completely enclosed light sources are permitted. Pendant fixtures and bare-lamp…

Key Concepts

Listing & Labeling (600.3) All fixed, mobile, or portable electric signs, section signs, outline lighting, PV-powered signs, and retrofit kits — regardless of voltage — must be listed, labeled, and installed per that listing. Two exceptions: field-installed skeleton tubing does not require listing, and outline lighting does not require system listing when it consists of listed luminaires wired per Chapter 3.

Branch Circuits (600.5) - Every commercial building/occupancy accessible to pedestrians must have at least one outlet at each tenant space entrance for sign use. - That outlet must be on a dedicated branch circuit rated at least 20 amperes that supplies no other load. - Neon sign branch circuits: rated no more than 30 amperes. -…

Key Concepts

Initiating Devices

• Manual fire alarm boxes (pull stations): must be accessible, unobstructed, mounted 42"–54" AFF per NFPA 72
• Heat detectors: Fixed-temperature (activates at set point) vs. rate-of-rise (activates on rapid temp increase); some are combination type
• Smoke detectors: Ionization (fast-flaming fires) vs. photoelectric (slow-smoldering fires)
• Flame detectors: Detect radiant energy (UV/IR); used where smoke/heat detection is impractical
• Supervisory switches: Monitor sprinkler control valves and other suppression system components — NOT initiating fire alarm signals, but supervisory signals

8 questions | 10% of exam | Reference: 29 CFR 1926

Key Concepts

Electrical Hazard Recognition & Guarding (OSHA 1926 Subpart K)

• Live parts operating at 50 volts or more must be guarded against accidental contact.
• Guarding methods: enclosures, barriers, elevation (minimum 8 feet above floor for unguarded live parts), or restricted access locations.
• Conductors and equipment must be approved and used only for their listed purpose.
• Qualified workers must have the training and experience to work on or near energized equipment. Unqualified workers must maintain safe approach distances.