Exam Cheat Sheet · Quick Reference
Idaho Limited Electrical Refrigeration, Heating & Air Conditioning Installer
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
45
Passing score
70%
Exam time
120 min
Administered by
PSI Services Contractor
Format
Reference materials allowed
Idaho State Portion 45 questions
2017 National Electrical Code, NFPA – Introduction
2 Q · 4%
Purpose and scope of the NEC (practical safeguarding of persons and property)NEC scope: covered and not-covered installations (90.2)Code arrangement and chapter hierarchy (90.3)Authority having jurisdiction (AHJ): enforcement powers and special permissionMandatory vs. permissive rules and explanatory material (shall/shall not vs. shall be permitted)Equipment examination, listing, and approval for safety (90.7)Units of measurement: SI and inch-pound dual system (90.9)Wiring planning for future expansion and circuit enclosure limitations (90.8)
2017 National Electrical Code, NFPA – Chapter 1
3 Q · 7%
Key NEC definitions and terminology (Article 100)Equipment approval, listing, and labeling requirementsElectrical connections, splices, and conductor temperature limitationsWorking space and clearance requirements around electrical equipmentGuarding of live parts and arc-flash hazard warningEquipment marking and identification of disconnecting meansEnclosure type selection for environmental conditionsWiring integrity, conductor materials, and approved wiring methodsArticle 100 - Definitions
2017 National Electrical Code, NFPA – Chapter 2
10 Q · 22%
Grounding and bonding requirements for services and separately derived systemsGrounding electrode system types, installation, and sizingEquipment grounding conductor types, sizing, and identificationBonding of piping systems, structural metal, and service equipmentGFCI and AFCI protection requirements for branch circuitsBranch-circuit load calculations and conductor ampacity requirementsOvercurrent protection devices, ratings, and location requirementsFeeder and service load calculation methods including demand factorsArticle 250 - Grounding and Bonding
2017 National Electrical Code, NFPA – Chapter 3
6 Q · 13%
Conductor ampacity tables and temperature correction/adjustment factors (Article 310)Conductor types, insulation designations, and permitted uses by location (Article 310)Protection of cables and raceways against physical damage through framing members and structural elements (Article 300)Underground wiring installation requirements and minimum burial depths (Article 300)Wiring in ducts, plenums, and air-handling spaces (Article 300)Box and conduit body fill calculations and minimum sizing for outlet, device, pull, and junction boxes (Article 314)Installation requirements for flexible conduit types: FMC, LFMC, and LFNC — uses, securing, and grounding (Articles 348, 350, 356)Installation requirements for rigid and nonmetallic conduit systems: RMC, EMT, and PVC — supports, bends, and grounding (Articles 344, 358, 352)Article 310 - Conductors for General Wiring
2017 National Electrical Code, NFPA – Chapter 4
16 Q · 36%
Motor branch-circuit conductor sizing and ampacity requirements (Article 430, Part II)Motor overload protection selection and settings (Article 430, Part III)Motor branch-circuit short-circuit and ground-fault protective device ratings (Article 430, Part IV)Motor disconnecting means types, ratings, and location requirements (Article 430, Part IX)Motor controller ratings, markings, and design requirements (Article 430, Parts VII–VIII)Air-conditioning and refrigerating equipment branch-circuit conductors, disconnecting means, and overload protection (Article 440)Fixed electric space-heating equipment branch circuits, overcurrent protection, and disconnecting means (Article 424)Appliance branch-circuit ratings, overcurrent protection, and disconnecting means (Article 422)Article 430 - Motors, Motor Circuits, and ControllersArticle 424 - Fixed Electric Space-Heating Equipment
2017 National Electrical Code, NFPA – Chapter 7
7 Q · 16%
Class 1, Class 2, and Class 3 circuit definitions and classificationsPower source requirements for Class 1, Class 2, and Class 3 circuitsOvercurrent protection for Class 1 circuitsWiring methods for Class 1, Class 2, and Class 3 circuitsSeparation requirements between Class 2/Class 3 and power circuitsCable types and listing requirements for Class 2, Class 3, and PLTC cablesInstallation of Class 2 and Class 3 cables in specific locations (plenums, risers, ducts)Circuits and equipment operating at less than 50 voltsArticle 725 - Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits
2017 National Electrical Code, NFPA Calculations
1 Q · 2%
Branch-circuit conductor sizing for motor loads (125% rule, Article 430.22)Motor branch-circuit short-circuit and ground-fault protective device ratings (Table 430.52)Motor overload protection selection and trip current percentages (Article 430.32)Hermetic refrigerant motor-compressor branch-circuit conductor ampacity (Article 440.32)Branch-circuit short-circuit and ground-fault protection for hermetic refrigerant motor-compressors (Article 440.22)Feeder and service load calculations including motor loads (Articles 220.40, 220.50)Conductors supplying multiple motors or combined motor and other loads (Articles 430.24, 440.33)Full-load current values from NEC motor tables (Tables 430.247, 430.248, 430.249, 430.250)Article 430 - Motors, Motor Circuits, and Controllers
Key Distinctions
Motor FLC from NEC Tables 430.247–430.250vsMotor nameplate current rating
Per 430.6(A)(1) the table values are used to size conductors, switches, and branch-circuit short-circuit/ground-fault protection, while the nameplate current is used only for sizing overload protection per 430.6(A)(2).
NEC 2017 Section 430.6(A)(1)Wye-start, delta-run motor conductors (controller to motor)vsPart-winding connected motor conductors (controller to motor)
430.22(C) requires not less than 72 percent of motor FLC (58% × 1.25) for wye-start/delta-run, while 430.22(D) requires not less than 62.5 percent (50% × 1.25) for part-winding motors; 125 percent applies to the line-side conductors in both cases.
NEC 2017 Section 430.22(C)Single-motor branch-circuit conductors (430.22)vsFeeder conductors for several motors (430.24)
Branch-circuit conductors for one continuous-duty motor must be at least 125% of that motor's FLC, while feeder conductors must be at least 125% of the HIGHEST rated motor's FLC plus 100% of the FLC of all other motors (plus non-motor loads).
NEC 2017 Section 430.22NEC 240.4(B) next higher standard OCPD ratingvsNEC 240.4(C) devices rated over 800 amperes
240.4(B) permits the next higher standard rating above conductor ampacity only where the selected rating does not exceed 800 amperes, whereas for devices rated over 800 amperes 240.4(C) requires conductor ampacity equal to or greater than the device rating.
NEC 2017 Section 240.4(B)Conductors requiring printed tag marking (310.120(B)(3))vsConductors requiring durable surface marking (310.120(B)(1))
Type MI cable, switchboard wires, metal-covered single-conductor cables, and Type AC cable are marked by a printed tag on the coil, reel, or carton, while nonmetallic-sheathed cable, service-entrance cable, and tray cable are surface marked.
NEC 2017 Section 310.120(B)(3)Supplementary overcurrent protectionvsRequired branch-circuit overcurrent device
Per 240.10 supplementary overcurrent protection shall not be used as a substitute for, or in place of, the required branch-circuit overcurrent device.
NEC 2017 Section 240.10Thermal relays for short-circuit/ground-fault protectionvsThermal relays for motor branch-circuit overload protection
Per 240.9 thermal relays and similar devices not designed to open short circuits or ground faults shall not protect conductors against short-circuit or ground-fault overcurrent, but they are permitted to protect motor branch-circuit conductors from overload when protected in accordance with 430.40.
NEC 2017 Section 240.9Transformer secondaries protected by the primary OCPDvsTransformer secondaries NOT protected by the primary OCPD
Per 240.4(F), 2-wire single-phase and delta-delta 3-wire secondary conductors are permitted to be protected by the primary-side device, while single-phase other than 2-wire and multiphase other than delta-delta 3-wire secondaries are not considered protected by it.
NEC 2017 Section 240.4(F)Motor overload trip limit — service factor 1.15 or greater / 40°C rise or lessvsMotor overload trip limit — all other motors
Under 430.32(C), when a higher sensing element or setting is used the trip current must not exceed 140 percent of nameplate FLC for motors marked SF 1.15 or greater or 40°C rise or less, versus 130 percent for all other motors (170 percent is a thermal-protector ultimate trip limit under 430.32(A)(2)).
NEC 2017 Section 430.32(C)Instantaneous trip breaker — Design B energy-efficient squirrel cage motorvsInstantaneous trip breaker — other AC polyphase motors
Table 430.52 permits a maximum of 1100% of full-load current for Design B energy-efficient squirrel cage motors versus a maximum of 800% for other AC polyphase motor types.
NEC 2017 Table 430.52Grounding per 250.4(A)(1)vsBonding of equipment per 250.4(A)(3)
System grounding serves the purposes in 250.4(A)(1), while bonding normally non-current-carrying conductive materials connects them together and to the supply source to establish an effective ground-fault current path; the earth shall not be considered an effective ground-fault current path per 250.4(A)(5).
NEC 2017 Section 250.4(A)(3)Class 2/Class 3 conductor separation in an outlet box — routed apart (725.136(D)(1))vsSeparation under the 'other applications' rule (725.136(I))
Where 120-volt power conductors are introduced solely to connect the equipment served by the Class 2/3 circuit and are routed apart rather than barriered, a minimum 6 mm (0.25 in.) separation is required, while the 50 mm (2 in.) figure applies to the other-applications rule.
NEC 2017 Section 725.136(D)(1)Key Terms
Ampacity (Article 100) NEC 2017
The maximum current, in amperes, a conductor can carry continuously under the conditions of use without exceeding its temperature rating.
Continuous Load (Article 100) NEC 2017 Article 100
A load where the maximum current is expected to continue for 3 hours or more.
Dwelling, Multifamily (Article 100) NEC 2017 Article 100 — Definitions, 'Dwelling, Multifamily'
A building containing three or more dwelling units; a building with exactly two units is a two-family dwelling.
Effective ground-fault current path (250.4(A)(5)) NEC 2017 Section 250.4(A)(5)
A low-impedance circuit capable of safely carrying the maximum ground-fault current to facilitate operation of the overcurrent device; the earth shall not be considered such a path.
Objectionable current (250.6(D)) NEC 2017 Section 250.6(D)
Currents that introduce noise or data errors in electronic equipment shall NOT be considered the objectionable currents addressed in 250.6, so they do not justify alterations to the grounding system.
Plug fuse identification (240.50(C)) NEC 2017 Section 240.50(C)
Plug fuses of 15-ampere and lower rating are identified by a hexagonal configuration of the window, cap, or other prominent part.
Adjustable-trip circuit breaker rating (240.6(B)) NEC 2017
Where the breaker has external means for adjusting the long-time pickup setting and does not meet 240.6(C) restricted access, its ampere rating is the maximum setting possible.
Ground-fault protection of equipment (240.13) NEC 2017 Section 240.13
Required for solidly grounded wye systems of more than 150 volts to ground but not exceeding 1000 volts phase-to-phase for each individual device used as a building or structure main disconnecting means rated 1000 amperes or more.
Coordination system (240.12) NEC 2017 Section 240.12
Where an orderly shutdown is required to minimize hazards, a system of coordination based on (1) coordinated short-circuit protection and (2) overload indication based on monitoring systems or devices is permitted.
Class 1 remote-control and signaling circuits (725.41(B)) NEC 2017 Section 725.41(B)
Class 1 circuits are not permitted to exceed 600 volts.
Class 1 power-limited source other than a transformer (725.41(A)(2)) NEC 2017 Section 725.41(A)(2)
Must be protected by an overcurrent device rated not more than 167 percent of the volt-ampere rating of the source divided by the rated voltage; the device may be integral to the supply but shall not be interchangeable with higher-rated devices.
Authority Having Jurisdiction (90.4) NEC 2017 Section 90.4
The authority having jurisdiction for enforcement of the Code is responsible for interpreting the rules, deciding on approval of equipment and materials, and granting special permission.
Mechanical execution of work — unused openings (110.12(A)) NEC 2017 Section 110.12(A)
Unused openings in boxes, raceways, and enclosures—other than those for equipment operation, mounting, or permitted as part of listed-equipment design—shall be effectively closed to afford protection substantially equivalent to the wall of the equipment.
Fixed storage-type water heater (422.13) NEC 2017 Section 422.13
A fixed storage-type water heater with a capacity of 450 L (120 gal) or less is considered a continuous load for sizing branch circuits.
Motor nameplate code letter marking (430.7(A)(8)) NEC 2017 Section 430.7(A)(8)
An alternating-current motor rated 1/2 hp or more must be marked with the code letter or locked-rotor amperes; the code letter is omitted on polyphase wound-rotor motors.
Grounded conductor identification, 6 AWG or smaller (200.6(A)) NEC 2017 Section 200.6(A)
Identified by a continuous white outer finish, a continuous gray outer finish, or three continuous white or gray stripes along its entire length on other than green insulation.
Formulas to Know
Minimum branch-circuit conductor ampacity for a single continuous-duty motor
Ampacity ≥ 125% × motor full-load current from the applicable NEC table (430.22(A)); example: 65 A × 1.25 = 81.25 AMinimum feeder conductor ampacity for several motors plus other loads
(125% × highest motor FLC) + sum of FLC of all other motors + 100% of noncontinuous non-motor load + 125% of continuous non-motor load (430.24); examples: (15.2 × 1.25) + 15.2 + 15.2 = 49.4 A; (28 × 1.25) + 14 + (10 × 1.25) = 61.5 AConductors between controller and motor — special motor connections
Wye-start, delta-run: ≥ 72% of motor FLC (58% × 1.25); part-winding connected: ≥ 62.5% of motor FLC (50% × 1.25)Inverse time circuit breaker for a single motor that fails to start
Standard setting up to 250% of FLC per Table 430.52(C)(1); where the motor fails to start it may be increased but shall in no case exceed 400% of FLC for motors of 100 A or less (300% above 100 A). Examples: 50 A × 2.5 = 125 A standard, 50 A × 4 = 200 A max; 60 A × 400% = 240 A maxHermetic refrigerant motor-compressor branch circuit
Conductors ≥ 125% × RLA (440.32) and OCPD rated not more than 175% × RLA (440.22(A)); example: RLA 20 A → conductors 25 A, OCPD 35 A maxMaximum feeder overcurrent device rating for a motor feeder (430.62(A))
Not greater than (largest branch-circuit short-circuit/ground-fault device rating + sum of FLC of the other motors); example: 60 + 22 + 14 = 96 A, so the next standard size at or below 96 A per 240.6(A) is 90 APart-winding start induction motor branch-circuit protection (430.4)
Each motor-winding connection shall have branch-circuit short-circuit and ground-fault protection rated at not more than one-half that specified by 430.52Minimum bending radius, Type MC cable with interlocked armor or corrugated sheath (330.24(B))
Radius = 7 × external diameter of the metallic sheath; example: 7 × 1.5 in. = 10.5 in.Dwelling general lighting plus small-appliance and laundry load (Article 220)
(sq ft × 3 VA/sq ft, Table 220.12 dwelling unit load) + (2 × 1,500 VA small-appliance) + 1,500 VA laundry; example: 2,000 sq ft → 6,000 + 3,000 + 1,500 = 10,500 VARaceway conductor fill and box fill (NEC 2020/2023 Chapter 9 and 314.16(B))
Exactly 2 conductors use the 31% column; over 2 conductors use 40% of raceway area, then divide by conductor area and drop a fraction below 0.8 (Note 7). Examples: 2 × 0.0366 = 0.073 sq in → ½ in. EMT (0.094 sq in at 31%); 2.343 sq in ÷ 0.0507 = 46.21 → 46 conductors. Box fill: spare volume ÷ 2.25 cu in per 12 AWG conductor; 18.0 − 18.00 = 0.00 cu in → 0 additional conductors