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' (required/prohibited actions), while permissive rules use 'shall be permitted' or 'shall not be required' (optional actions).
Article 90.5(A)NEC Chapters 1–7vsNEC Chapter 8 (Communications Systems)
Chapters 1–7 apply generally or to special conditions, while Chapter 8 is NOT subject to Chapters 1–7 requirements except where specifically referenced in Chapter 8.
NEC 90.3SI UnitsvsInch-Pound Units
Per NEC 90.9(D), compliance with numbers shown in either the SI system or the inch-pound system constitutes compliance with the Code; both are equally valid.
Article 90.9(D)Direct Burial Cable (underground)vsRigid Metal Conduit / IMC (underground)
Direct burial cable requires a minimum cover of 600 mm (24 in.) in general locations, whereas rigid metal conduit or IMC requires only 150 mm (6 in.).
NEC Table 300.5(A)Bored Hole Protection (wood members)vsNotch Protection (wood members)
Bored holes must keep cable edges at least 32 mm (1-1/4 in.) from the wood edge, while cables in notches must be covered by a steel plate at least 1.6 mm (1/16 in.) thick.
NEC 300.4(A)(1)Series Circuit CurrentvsSeries Circuit Resistance
In a series circuit, current is the same in every part (IT = I1 = I2 = I3), whereas total resistance is the sum of all individual resistances (RT = R1 + R2 + R3).
Series Circuits120/240 V Single-Phase Three-Wire Systemvs120/208 V Three-Phase Four-Wire Wye System
The single-phase system uses black and red for ungrounded conductors with white/gray neutral, while the three-phase wye system uses A=black, B=red, C=blue for ungrounded conductors.
Ugly's Electrical References, Common Electrical Distribution SystemsDelta High-Leg (B phase) to NeutralvsStandard Phase to Neutral (120/240 V delta)
In a 120/240 V three-phase four-wire delta system, the B phase (orange high leg) measures 208 V to neutral, while standard phases measure 120 V to neutral.
Ugly's Electrical References, Common Electrical Distribution SystemsContinuous Load Feeder SizingvsNoncontinuous Load Feeder Sizing
Feeder conductors must be sized at 125% of continuous loads, whereas noncontinuous loads are added at 100% to determine minimum conductor ampacity.
NEC 215.2(A)(1)Vertically Operated Switch Handle (Up)vsVertically Operated Switch Handle (Down)
Per NEC 404.7, the up position of a vertically operated switch handle is the closed (on) position, implying the down position is the open (off) position.
NEC 404.7NEC PurposevsNEC as Design Specification
The NEC's purpose is the practical safeguarding of persons and property from electrical hazards; it is explicitly NOT intended as a design specification or instruction manual for untrained persons.
Article 90.2(A)Elevator Raceway Fill (Article 620)vsStandard Raceway Fill (Chapter 9, Table 1)
Elevator installations allow a maximum of 50% raceway fill for individual conductors under Article 620.33, which differs from the standard fill percentages in Chapter 9, Table 1.
Article 620.33Key Terms
NEC Purpose (Article 90.1(A)) Article 90.2(A)
The practical safeguarding of persons and property from hazards arising from the use of electricity; the Code is not a design specification or instruction manual for untrained persons.
Mandatory Rule (Article 90.5(A)) Article 90.5(A)
An NEC rule that specifically requires or prohibits an action, identified by the terms 'shall' or 'shall not'.
Permissive Rule (NEC 90.5(B)) NEC 90.5(A) and 90.5(B)
An NEC rule that identifies an action that is allowed but not required, identified by the terms 'shall be permitted' or 'shall not be required'.
Authority Having Jurisdiction / AHJ (Article 90.4) Article 90.4(B)
The body responsible for making NEC rule interpretations, approving equipment and materials, and granting special permissions.
NEC Exclusions (Article 90.2(B)) Article 90.2(D)
Installations NOT covered by the NEC include ships, watercraft (other than floating buildings), railway rolling stock, aircraft, and automotive vehicles (other than mobile homes and RVs).
NEC Code Structure (NEC 90.3) NEC 90.3
The NEC is divided into an introduction and nine chapters; Chapters 1–4 apply generally, Chapters 5–7 apply to special conditions, Chapter 8 covers communications (independent of Chapters 1–7), and Chapter 9 consists of tables.
SI / Inch-Pound Compliance (Article 90.9(D)) Article 90.9(D)
Compliance with measurements shown in either the SI system or the inch-pound system constitutes compliance with the NEC.
Minimum Service Rating – One-Family Dwelling (NEC 230.79(C)) NEC 230.79(C)
A one-family dwelling must have a service disconnecting means rated not less than 100 amperes, 3-wire.
Overhead Service Conductor Clearance – Public Streets (NEC 230.24(B)) NEC 230.24(B)
Overhead service conductors not exceeding 1000 V must maintain a minimum clearance of 5.5 m (18 ft) over public streets, alleys, and areas subject to truck traffic.
Ampacity Adjustment Factor – 7 to 9 Conductors (NEC Table 310.15(C)(1)) NEC Table 310.15(C)(1)
When 7–9 current-carrying conductors are bundled in a raceway or cable, conductor ampacity must be derated to 70% of the standard table values.
Table 310.16 Ambient Temperature Basis (NEC 310.16) NEC 310.16
Ampacity values in Table 310.16 are based on a 30°C (86°F) ambient temperature; correction factors must be applied for higher temperatures.
AC Conductors in Ferrous Metal Enclosures (NEC 300.20(A)) NEC 300.20(A)
All phase conductors, grounded conductors, and equipment grounding conductors carrying AC must be grouped together in ferrous metal enclosures to prevent induction heating.
Ohm's Law Ohm's Law Formulas
The mathematical relationship between voltage (E), current (I), and resistance (R): I = E ÷ R, E = I × R, R = E ÷ I.
Power Formula (Watt's Law) Ohm's Law Power Formulas
Power in watts equals voltage multiplied by current (P = E × I); rearranged: I = P ÷ E or E = P ÷ I.
High Leg (B Phase) in Delta System Ugly's Electrical References, Common Electrical Distribution Systems
In a 120/240 V three-phase four-wire delta system, the B phase (orange conductor) is the high leg measuring 208 V to the grounded neutral.
Minimum Copper Conductor Size (NEC 310.3(A)) NEC 310.3(A)
The minimum conductor size for general wiring rated up to 2000 V is 14 AWG copper or 12 AWG aluminum/copper-clad aluminum.
Formulas to Know
Ohm's Law – Current
I (amperes) = E (volts) ÷ R (ohms)Ohm's Law – Voltage
E (volts) = I (amperes) × R (ohms)Ohm's Law – Resistance
R (ohms) = E (volts) ÷ I (amperes)Power Formula – Power
P (watts) = E (volts) × I (amperes)Power Formula – Current from Watts
I (amperes) = P (watts) ÷ E (volts)Series Circuit – Total Resistance
RT = R1 + R2 + R3 + ...Series Circuit – Current (same throughout)
IT = I1 = I2 = I3Feeder Minimum Ampacity (Continuous + Noncontinuous Loads)
Min. Ampacity = (Noncontinuous Load × 1.00) + (Continuous Load × 1.25)