Idaho Master Electrician Exam

Key Concepts

Ohm's Law & Power Formulas

The four fundamental quantities — Voltage (E/V), Current (I), Resistance (R), and Power (P) — are related by: - E = I × R (and all transpositions) - P = E × I (and all transpositions) - P = I² × R and P = E²/R

Series Circuit Rules

• Total resistance: R_total = R₁ + R₂ + R₃...
• Current is the same through every component
• Voltage drops add up to equal source voltage (Kirchhoff's Voltage Law)
• Power: P_total = P₁ + P₂ + P₃...

NEC Scope — Covered vs. Not Covered (Article 90.2)

Covered (90.2(C)): Public and private buildings, mobile homes, RVs, floating buildings, yards, parking lots, carnivals, industrial substations, marina shore power, and utility-owned office/warehouse buildings not integral to a generating plant.

Key Concepts

Article 215 – Feeders - Feeder conductors must have ampacity ≥ noncontinuous load + 125% of continuous load (215.2(A)(1)) - Feeder OCPDs must be rated ≥ noncontinuous load + 125% continuous load (215.3) - Exception: 100%-rated assemblies may use sum of continuous + noncontinuous without the 125% multiplier - Feeder grounded conductor ≥ size required by 250.122 (equipment grounding conductor table)

Article 230 – Services - Service entrance conductors must be sized for the calculated load; service disconnect must be ≤ 6 disconnects in one location - Ground-fault protection required on solidly grounded wye systems >150V-to-ground, ≤1000V phase-to-phase, for disconnects rated ≥1000A (230.95) - Service conductors are considered outside the building until they enter through an exterior wall or raceway

Key Concepts

Article 300.4 — Physical Damage Protection - Bored holes through wood members: edge of hole must be ≥ 1¼ in. from the nearest edge of the wood member. - If that distance can't be maintained, install a steel plate ≥ 1/16 in. thick to protect the wiring. - Exception: Steel plates are not required for RMC, IMC, rigid PVC conduit, RTRC, or EMT. - Cables in notches in wood must be protected by a ≥ 1/16 in. steel plate installed before the building finish is applied.

Article 300.5 — Underground Installation Cover Depths - Minimum cover depths vary by wiring method and location. Key values to memorize: - Direct burial conductors (residential 120V, 20A GFCI): 12 in. - RMC or IMC: 6 in. - GFCI-protected or GFCI + physical damage protected (residential): 12 in. - General direct burial (not GFCI): 24 in. - Under a building slab: 0 in. (no minimum cover required)

Key Concepts

Article 400 — Flexible Cords - Flexible cords are not permitted as a substitute for permanent wiring, run through walls/ceilings/floors, or concealed behind building surfaces (400.12). - Permitted uses include pendants, wiring of luminaires, portable equipment connections, and elevator wiring. - Type S, SO, SOW = 600V, extra-hard usage, damp/wet locations. Type SJ, SJO = 300V, hard usage. Type C (lamp cord) = dry locations only, not hard usage. - Ampacity is determined by Table 400.5(A)(1) — e.g., 18 AWG = 10A, 16 AWG = 13A, 14 AWG = 18A (for 2-conductor cords).

Article 402 — Fixture Wire - Minimum size: 18 AWG. Voltage limit: 600V or less for most types. - Types TF, TFF, XF, XFF, ZF are common fixture wire designations. - Fixture wire is not a substitute for branch-circuit conductors and is limited in use to wiring within luminaire fixtures or connecting luminaires to branch circuits.

(11 questions, 11% of exam — NEC 2023)

Key Concepts

Hazardous Location Classification (Article 500)

Class I — Flammable gases or vapors (gas stations, paint spray booths) Class II — Combustible dusts (grain elevators, flour mills, coal handling) Class III — Ignitible fibers/flyings (textile mills, sawmills) — not suspended in air like Class II

Division 1 — Hazardous concentrations exist under normal operating conditions Division 2 — Hazardous concentrations exist only under abnormal conditions (failure, accident, etc.)

• Each room/section/area is classified individually per 500.5(A)
• Area classification must be documented on a classification drawing and available to the AHJ per 500.4
• Equipment must be identified for the specific Class, Division, and Group

Sealing Requirements (Articles 501–503)

Articles 445, 600, 610, 620, 670 | 6 Questions (6%)

Key Concepts

Article 600 — Electric Signs & Outline Lighting

• Listing required (600.3): All fixed, mobile, or portable signs must be listed and labeled. Exception: field-installed skeleton tubing and outline lighting using listed luminaires wired per Chapter 3.
• Branch circuit requirement (600.5(A)): Every commercial building with pedestrian access must have at least one 20A branch circuit at each tenant space entrance, supplying no other load, for sign use.
• Branch circuit ratings (600.5(C)): Neon signs — max 30A. All other signs — max 20A. Treat sign loads as continuous loads.
• Disconnecting means (600.6): Each sign must have an externally operable switch or circuit breaker opening all ungrounded conductors, controlling no other load. Must be within sight of the sign or lockable in the open position. Exceptions: exit directional signs inside a building; cord-and-plug connected signs.

Key Concepts

Hazardous Location Classification (Article 500)

Classes define the type of hazardous material: - Class I – Flammable gases or vapors (e.g., gasoline, propane) - Class II – Combustible dusts (e.g., grain, coal, metal dust) - Class III – Ignitible fibers/flyings (e.g., sawdust, textile fibers)

Divisions define the likelihood of the hazard being present: - Division 1 – Hazardous conditions exist under normal operating conditions - Division 2 – Hazardous conditions exist only under abnormal conditions (e.g., equipment failure)

Protection Techniques: - Explosionproof (Class I only) – Enclosure contains an explosion and prevents ignition of surrounding atmosphere (500.7(A)) - Dust-ignitionproof (Class II) – Excludes dusts and won't ignite surrounding dust (502.10) - Intrinsically safe – Circuit energy too low to ignite hazardous atmosphere under normal or fault conditions (500.7(E)) - Purged/Pressurized – Maintains positive pressure with clean air/inert gas to prevent ignition (500.7(D))

Key Concepts

Article 800 – General Scope Article 800 establishes general requirements for all communications systems. Only NEC Chapters 1–7 sections explicitly referenced in Chapter 8 apply to Chapter 8 installations (800.3). This is a critical scope rule.

Cable Types & Listing Requirements by Location Communications cables must be listed for their specific environment: - Plenum (CMP) – highest rating; required in spaces used for environmental air handling (plenums per 300.22(C)) - Riser (CMR) – required in vertical runs through floor-to-floor shafts - General-purpose (CM) – for general horizontal runs - Limited-use (CMX) – lowest rating; restricted to residential and raceway use - Cable substitution hierarchy flows downward: CMP can substitute for CMR, CM, or CMX; CMX cannot substitute upward. - Plenum cable ties and nonmetallic accessories in plenums must be listed for low smoke and heat release (800.24).