Exam Cheat Sheet · Quick Reference
Idaho Master Electrician Exam
Idaho · PSI Services Contractor
Verified, not estimated. Every figure below is drawn from the official exam structure we maintain — question counts, passing standard and topic weighting. Practice questions are grounded in the source law with statute citations. We omit any figure we can't verify rather than guess at it.
Total questions
100
Passing score
75%
Exam time
270 min
Administered by
PSI Services Contractor
Format
Reference materials allowed
Idaho State Portion 100 questions
General Electrical Knowledge
10 Q · 10%
Ohm's Law formulas and calculations (voltage, current, resistance, power)Series circuit rules and calculationsNEC scope: installations covered and not coveredNEC code arrangement and chapter organizationMandatory vs. permissive vs. explanatory rule languageCommon electrical distribution systems and conductor color codingAuthority having jurisdiction (AHJ) enforcement and special permissionNEC units of measurement (SI and inch-pound systems)
Wiring and Protection
25 Q · 25%
Conductor ampacity tables and correction/adjustment factors (Articles 310.15-310.21)Grounding and bonding requirements including grounding electrode systems and conductors (Article 250)Protection of conductors against overcurrent including fuses and circuit breakers (Article 240)Underground wiring installation requirements and minimum cover depths (Article 300.5)Physical protection of cables and raceways through structural members (Article 300.4)Service entrance conductors, disconnecting means, and overcurrent protection (Article 230)Conductor types, insulation ratings, and permitted uses by location (Article 310.4 and 310.10)Feeder conductor sizing, overcurrent protection, and identification requirements (Article 215)Wiring methods permitted in ducts, plenums, and air-handling spaces (Article 300.22)Electrical continuity and mechanical continuity requirements for raceways and conductors (Articles 300.10–300.13)Equipment grounding conductor types, sizing, and identification (Article 250.118–250.122)Bonding requirements for piping systems, structural metal, and service equipment (Article 250.92–250.104)
+3 more
Wiring Methods and Materials
20 Q · 20%
Box fill calculations and conductor count requirements (Article 314.16)Conductor ampacity tables and temperature ratings (Article 310.14-310.21)Protection of cables and raceways against physical damage (Article 300.4)Underground installation requirements and minimum cover depths (Article 300.5)Support and securing of boxes and enclosures (Article 314.23)Wiring in ducts, plenums, and air-handling spaces (Article 300.22)Pull and junction box sizing for conductors 4 AWG and larger (Article 314.28)General raceway installation requirements including continuity, sealing, and conductor grouping (Article 300.6-300.20)Conductor identification requirements for grounded, equipment grounding, and ungrounded conductors (Article 310.6)Conductor types and insulation applications for dry, damp, and wet locations (Article 310.10)Minimum conductor size and material requirements including aluminum AA-8000 alloy (Article 310.3)Firestopping requirements for electrical penetrations through fire-rated assemblies (Article 300.21)
+2 more
Equipment for General Use
20 Q · 20%
Fixture wire types, temperature ratings, and voltage limitations (Article 402)Receptacle installation, grounding, and replacement requirements (Article 406)Luminaire location requirements for wet, damp, and specific locations (Article 410)Switch ratings, connections, and installation requirements (Article 404)Flexible cord types, permitted and prohibited uses, and ampacity (Article 400)Luminaire support methods and grounding requirements (Article 410)Lighting track installation requirements and restrictions (Article 410 Part XIV)Recessed luminaire clearance, thermal protection, and wiring requirements (Article 410)Motor branch-circuit conductor sizing, overload protection, and disconnecting means (Article 430)Air-conditioning and refrigeration equipment conductor and OCPD sizing (Article 440)Transformer overcurrent protection and installation requirements (Article 450)Generator installation and overcurrent protection (Article 445)
Special Occupancies
11 Q · 11%
Hazardous location classification (Class I, II, III; Division 1 and 2) and area classification requirementsWiring methods and sealing requirements for Class I, II, and III hazardous locationsCommercial garages and motor fuel dispensing facility area classification and wiring requirementsHealth care facility essential electrical systems (Type 1 and Type 2 EES), life safety and critical branch requirementsPatient care space wiring, grounding, bonding, and receptacle requirements in health care facilitiesSwimming pool and spa electrical installation requirements including GFCI protection, bonding, and luminaire placementMobile and manufactured home electrical systems including power supply, branch circuits, grounding, and service equipmentAssembly occupancy wiring methods, temporary wiring, and supply requirements
Special Equipment
6 Q · 6%
Wiring methods and conductor types for cranes and hoists (Article 610)Disconnecting means requirements for cranes, hoists, and elevatorsOvercurrent and overload protection for crane, hoist, and elevator circuitsElevator and escalator branch circuits, feeder sizing, and demand factors (Article 620)Generator installation, marking, overcurrent protection, and disconnecting means (Article 445)Electric signs and outline lighting disconnects, branch circuits, and grounding (Article 600)Industrial machinery nameplate data, supply conductor sizing, and short-circuit current rating (Article 670)Grounding and bonding requirements for cranes, hoists, and elevators
Special Conditions
5 Q · 5%
Hazardous location classification (Class I, II, III and Division 1 and 2)Protection techniques for hazardous locations (explosionproof, dust-ignitionproof, intrinsically safe, purged/pressurized, etc.)Solar PV system circuit requirements (maximum voltage, current calculations, overcurrent protection, and arc-fault protection)Solar PV rapid shutdown requirements and labelingHealth care facility essential electrical systems (Type 1 and Type 2 EES branches)Wiring methods and sealing requirements for Class I hazardous locationsHealth care facility patient care space grounding, bonding, and isolated power systemsPark trailer electrical systems (power supply, branch circuits, grounding, and GFCI requirements)
Communication Systems
3 Q · 3%
Cable types and listing requirements by location (plenum, riser, general-purpose, limited-use)Grounding and bonding of communications cables, primary protectors, and cable shieldsSeparation requirements between communications cables and power/light conductorsPrimary and secondary protector requirements and placementOverhead aerial wiring clearances and installation requirements for communications cablesNetwork-powered broadband communications systems power classifications and cable types (Article 830)Antenna system installation, grounding, and clearance requirements (Article 810)CATV coaxial cable grounding, bonding, and cable substitution requirements (Article 820)
Key Distinctions
Mandatory NEC rulesvsPermissive NEC rules
Mandatory rules use "shall" or "shall not" (90.5(A)), while permissive rules use "shall be permitted" or "shall not be required" (90.5(B)).
NEC 2023 Section 90.5(A) and 90.5(B)NEC Chapters 1 through 7vsNEC Chapter 8 (communications systems)
Chapters 1–4 apply generally and 5–7 to special conditions, but Chapter 8 is not subject to Chapters 1 through 7 except where specifically referenced in Chapter 8.
NEC 2023 Section 90.3NEC purpose (practical safeguarding)vsDesign specification / instruction manual
Per 90.1(A) the Code's purpose is the practical safeguarding of persons and property from electrical hazards; it is NOT intended as a design specification or instruction manual for untrained persons.
NEC 2023 Section 90.1(A)12 AWG copper THWN (75°C)vs12 AWG copper THWN-2 (90°C)
In Table 310.16 (not more than three current-carrying conductors in raceway, 30°C ambient), THWN is 25 amperes while THWN-2 at the 90°C column is 30 amperes.
NEC 2023 Table 310.16Direct-buried cable covervsRMC/IMC cover
In "all locations not specified" in Table 300.5(A), direct-buried cables/conductors need 600 mm (24 in.) of cover while rigid metal or intermediate metal conduit needs only 150 mm (6 in.).
NEC 2023 Table 300.5(A)RMC in "all locations not specified"vsRMC under a one- or two-family dwelling driveway
The 150 mm (6 in.) RMC figure applies only to locations not specified, whereas a dwelling driveway/outdoor parking area is a specified row requiring 450 mm (18 in.); general streets, roads, alleys and parking lots require 600 mm (24 in.) for all wiring methods.
NEC 2023 Table 300.5(A)Standard direct-burial cable (24 in.)vsGFCI-protected residential branch circuit, 120 V or less, max 20 A OCPD (12 in.)
Table 300.5(A) Column 1 requires 600 mm (24 in.) for direct-buried cable, but Column 4 permits a reduced 300 mm (12 in.) cover for GFCI-protected residential branch circuits rated 120 V or less with maximum 20-ampere overcurrent protection in locations not otherwise specified.
NEC 2023 Table 300.5(A)Overhead service clearance over public streets/alleysvsOverhead service clearance over residential property and driveways
Per 230.24(B), conductors not over 1000 V need 5.5 m (18 ft) over public streets, alleys, roads and areas subject to truck traffic, but only 3.7 m (12 ft) over residential property and driveways (and commercial areas not subject to truck traffic) where voltage does not exceed 300 volts to ground.
NEC 2023 Section 230.24(B)Elevator raceway conductor fill (Article 620.33)vsGeneral conduit fill (Chapter 9, Table 1)
Elevator installations permit the sum of conductor cross-sectional areas to reach 50 percent of the raceway interior area, differing from the standard Chapter 9 Table 1 percentages (40 percent for three or more conductors).
NEC 2023 Section 620.33Exactly two conductors in a raceway (31% fill)vsOver two conductors in a raceway (40% fill)
Chapter 9, Table 1 uses the 31 percent column when exactly two conductors are installed and the 40 percent column when there are more than two conductors.
NEC 2023 Chapter 9, Table 1 (percent fill)Minimum conductor size for general wiring up to 2000 VvsMinimum size for overhead service conductors
General wiring minimum is 14 AWG copper (or 12 AWG aluminum/copper-clad aluminum) except as permitted elsewhere, while overhead service conductors shall not be smaller than 8 AWG copper or 6 AWG aluminum/copper-clad aluminum.
NEC 2023 Section 310.3(A)Box-fill allowance for a device yokevsBox-fill allowance for clamps and equipment grounding conductors
314.16(B)(4) requires double volume for each yoke/strap (based on largest conductor connected), while 314.16(B)(2) gives a single allowance for all internal clamps and (B)(5) gives one allowance for up to four EGCs plus 1/4 allowance for each additional EGC.
NEC 2023 Section 314.16(B)(1) through (B)(5)Key Terms
Authority Having Jurisdiction (AHJ) NEC 2023 Section 90.4(B)
Per 90.4, the enforcement authority responsible for interpreting Code rules, deciding on approval of equipment and materials, and granting special permission contemplated by the rules.
Installations not covered by the NEC NEC 2023 Section 90.2(D)
Per Article 90.2, the Code does not cover installations in ships, watercraft other than floating buildings, railway rolling stock, aircraft, or automotive vehicles other than mobile homes and recreational vehicles.
Free conductor length (300.14) NEC 2023 Section 300.14
At least 150 mm (6 in.) of free conductor, measured from where it emerges from the raceway or cable sheath in the box, must be left at each outlet, junction, and switch point for splices or connection of luminaires/devices.
Conductors of the same circuit (300.3(B)) NEC 2023 Section 300.3(B)
All conductors of the same circuit, including the grounded conductor, equipment grounding conductors, and bonding conductors, must be in the same raceway, conduit body, auxiliary gutter, cable tray, cablebus, trench, cable, or cord unless otherwise permitted.
Steel plate protection (300.4) NEC 2023 Section 300.4(A)(2)
Cables or raceways laid in notches in wood members must always be protected by a steel plate (or bushing) at least 1.6 mm (1/16 in.) thick of appropriate length and width; the same 1.6 mm (1/16 in.) plate/bushing is required where the 32 mm (1 1/4 in.) distance from the edge of a bored hole or from the edge of a framing member run parallel cannot be maintained.
Stranded conductor requirement (310.3(C)) NEC 2023 Section 310.3(C)
Conductors 8 AWG and larger installed in raceways shall be stranded unless specifically permitted or required elsewhere in the Code to be solid.
Table 310.16 basis NEC 2023 Section 310.16
Ampacities in Table 310.16 are based on a 30°C (86°F) ambient temperature, with correction factors applied for other ambients.
Vertical raceway conductor support (Table 300.19(A)) NEC 2023 Table 300.19(A)
Copper conductors 18 AWG through 8 AWG and 6 AWG through 1/0 AWG in vertical raceways must be supported at intervals not greater than 30 m (100 ft), including at the top of the rise.
Service disconnecting means rating, one-family dwelling (230.79(C)) NEC 2023 Section 230.79(C)
The service disconnecting means for a one-family dwelling shall be rated not less than 100 amperes, 3-wire.
Service-entrance cable support (230.51(A)) NEC 2023 Section 230.51(A)
Service-entrance cables must be supported by straps or other approved means within 300 mm (12 in.) of every service head, gooseneck, or connection to a raceway or enclosure.
Protection of emerging direct-buried cable (300.5(D)(1)) NEC 2023 Section 300.5(D)(1)
Direct-buried conductors and cables emerging from grade must be protected by enclosures or raceways from the minimum required cover depth to at least 2.5 m (8 ft) above finished grade.
Grounding electrode conductor physical protection (250.64(B)(2)) NEC 2023 Section 250.64(B)(2)
A 6 AWG or larger copper, copper-clad aluminum, or aluminum grounding electrode conductor exposed to physical damage must be protected in RMC, IMC, Schedule 80 PVC, RTRC-XW, EMT, or cable armor.
Multiple rod/pipe/plate electrode spacing (250.53(A)(3)) NEC 2023 Section 250.53(A)(3)
Where multiple rod, pipe, or plate electrodes are installed to meet the supplemental electrode requirement, they shall be not less than 1.8 m (6 ft) apart.
Pull point (358.26) NEC 2023 Section 358.24(B)
A point such as a conduit body between which raceway bends are counted; bends are limited to 360 degrees between pull points, so each section on either side of an added conduit body may have up to 360 degrees.
Array boundary for PV rapid shutdown (690.12(B)) NEC 2023 Section 690.12(B)
The array boundary is defined as 305 mm (1 ft) from the array in all directions; controlled conductors outside that boundary and more than 1 m (3 ft) from the array, or inside a building, must be limited to not more than 30 volts within 30 seconds of rapid shutdown initiation.
Type BLP cable (800.179(A)) NEC 2023 Section 800.179(A)
Network-powered broadband communications low-power plenum cable, listed as suitable for ducts, plenums, and other environmental air spaces with adequate fire-resistant and low-smoke-producing characteristics (BLR = low-power riser, BMR = medium-power riser, BLX = limited use).
Stationary generator listing (445.6) NEC 2023 Section 445.6
Stationary generators shall be listed, except one-of-a-kind or custom-manufactured units, which are permitted to be field labeled.
Series circuit Rule 1 Ugly's Electrical References, 2023 ed., Series Circuits, Page 3 (2020 ed.: Series Circuits)
Total current in a series circuit equals the current in any other part of the circuit (IT = I1 = I2 = I3).
120/240-volt delta high-leg system Ugly's Electrical References, 2023 ed., Common Electrical Distribution Systems, Page 13 (2020 ed.: Common Electrical Distribution Systems)
A system in which 208 volts exists between the orange (B phase) high leg and the white (neutral) conductor.
Conductor color identification (common distribution systems) Ugly's Electrical References, 2023 ed., Common Electrical Distribution Systems, Page 13 (2020 ed.: Common Electrical Distribution Systems)
In a 120/240-volt single-phase three-wire system the grounded neutral is white or gray and the ungrounded conductors are black (line 1) and red (line 2); in a 120/208-volt three-phase four-wire wye the C phase is blue.
Formulas to Know
Ohm's law basic relationships
I = W ÷ V (1500 W ÷ 120 V = 12.5 A); R = V ÷ I (240 V ÷ 8 A = 30 Ω); E = I × R (10 A × 12 Ω = 120 V)Power (watts) from Ohm's law
P = E × I (volts × amperes); P = E² ÷ R (e.g., 240² ÷ 20 Ω = 2880 W)Minimum feeder / service-entrance conductor ampacity with continuous load
Minimum ampacity = noncontinuous load + (125% × continuous load); e.g., 40 A + (1.25 × 80 A) = 140 A; 40 A + (1.25 × 60 A) = 115 A; (100 A × 1.25) + 30 A = 155 A. Applies where the OCPD/assembly is not listed for 100 percent rating.Ampacity of parallel conductor sets
Total ampacity = table ampacity × number of parallel sets; 350 kcmil THHN copper (90°C column, Table 310.16) = 350 A, two sets = 700 AAmpacity adjustment for more than three current-carrying conductors
Multiply table ampacity by the Table 310.15(C)(1) factor; for 7–9 current-carrying conductors use 70 percentConduit fill check (Chapter 9, Table 1)
Allowable area = raceway internal cross-sectional area × 40% (more than two conductors) or × 31% (exactly two); conduit area = πr²; total conductor area = sum of each conductor's area, including the equipment grounding conductor at its actual area (e.g., 4 × 0.0507 + 4 × 0.0133 + 1 × 0.0133 = 0.269 sq in.)Maximum number of same-size conductors in a raceway (Note 7 rounding)
N = (40% area of raceway) ÷ (area per conductor), dropping the fraction when it is below 0.8; e.g., 1½" EMT: 0.814 ÷ 0.0507 = 16.06 → 16; 2½" EMT: 2.343 ÷ 0.0507 = 46.21 → 46Box fill volume allowances (314.16(B))
Total allowances = one per current-carrying conductor + one for all internal clamps + two per device yoke/strap + one for up to four EGCs (plus 1/4 for each EGC beyond four); multiply by per-conductor volume (12 AWG = 2.25 in³, 14 AWG = 2.00 in³). Example: 4 + 1 + 2 + 1 = 8 allowances × 2.25 = 18.0 in³Additional conductors a box can accept
Spare volume = box volume − required fill volume; additional conductors = spare ÷ per-conductor volume, whole numbers only (18.0 − 18.00 = 0 ÷ 2.25 = 0; 25.5 − 24.00 = 1.50 ÷ 2.00 = 0.75 → 0)Dwelling general load calculation (Article 220)
Total VA = (floor area × 3 VA per sq ft) + (1500 VA × number of small-appliance circuits) + (1500 VA × number of laundry circuits); e.g., 2000 sq ft: 6000 + 3000 + 1500 = 10,500 VA; per-unit totals are multiplied by the number of units before demand factors (8100 × 4 = 32,400 VA); dwelling units only: a retail store uses the Table 220.42(A) unit load, 1.9 VA/sq ft, plus 180 VA per receptacle outletMinimum straight-pull box length (314.28(A)(1))
Length = 8 × trade size of largest raceway; 8 × 3 in. = 24 in. (610 mm)