Exam Cheat Sheet · Quick Reference
Idaho Limited Electrical Well Driller
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
40
Passing score
70%
Exam time
120 min
Administered by
PSI Services Contractor
Format
Reference materials allowed
Idaho State Portion 40 questions
2017 National Electrical Code, NFPA – Introduction
3 Q · 8%
Purpose and scope of the NEC (practical safeguarding of persons and property)What installations are covered and not covered under NEC scope (90.2)Code arrangement and chapter organization (Chapters 1–9, annexes)Authority having jurisdiction (AHJ) roles, enforcement, and special permissionsMandatory vs. permissive rules and explanatory material (shall/shall not vs. shall be permitted)Equipment examination, listing, and approval for safety (90.7)Wiring planning for future expansion and circuit limitations in enclosures (90.8)Units of measurement: SI and inch-pound dual system (90.9)
2017 National Electrical Code, NFPA – Chapter 1
4 Q · 10%
Key NEC definitions (Article 100 terms: grounded, bonded, ampacity, overcurrent, service, feeder, branch circuit)Equipment approval, listing, and labeling requirementsExamination and identification criteria for electrical equipment (110.3)Electrical connections: terminals, splices, and conductor temperature limitationsWorking space and clearances around electrical equipment (110.26)Guarding of live parts and arc-flash hazard warning requirementsEnclosure type selection (Table 110.28 indoor/outdoor ratings)Wiring integrity, conductor materials, and interrupting ratingsArticle 100 - Definitions
2017 National Electrical Code, NFPA – Chapter 2
14 Q · 35%
Grounding and bonding requirements for grounded and ungrounded AC systems (Article 250)Grounding electrode system types, installation, and sizing (250.50–250.70)Equipment grounding conductors: types, sizing, and identification (250.118–250.122)Bonding of services, piping systems, and structural metal (250.90–250.106)GFCI and AFCI protection requirements for branch circuits (Article 210)Branch-circuit ratings, conductor sizing, and overcurrent protection (Articles 210 and 240)Branch-circuit, feeder, and service load calculations including demand factors (Article 220)Outside branch circuits and feeders: clearances, disconnecting means, and wiring methods (Article 225)Article 250 - Grounding and BondingArticle 210 - Branch Circuits
2017 National Electrical Code, NFPA – Chapter 3
8 Q · 20%
Conductor ampacity tables and adjustment factors (Art. 310)Wiring method installation requirements and physical protection (Art. 300)Underground installation cover requirements and burial depth (Art. 300/310)Box and conduit body fill calculations and sizing (Art. 314)Conduit types, uses permitted, and securing/supporting requirements (RMC, IMC, EMT, PVC, FMC, LFMC, LFNC)Cable types, uses permitted, and installation requirements (NM, MC, SE, USE, UF)Conductor identification, marking, and insulation type designations (Art. 310)Cabinet and enclosure wiring space, deflection, and wire-bending requirements (Art. 312)Article 310 - Conductors for General Wiring
2017 National Electrical Code, NFPA – Chapter 4
10 Q · 25%
Motor branch-circuit conductor sizing and ampacity requirements (Article 430, Part II)Motor overload protection devices and trip current settings (Article 430, Part III)Motor branch-circuit short-circuit and ground-fault protective device ratings and Table 430.52Motor disconnecting means types, location, and ampere rating requirements (Article 430, Part IX)Motor controller ratings, marking, and design requirements (Article 430, Part VII)Flexible cord and cable permitted uses, prohibited uses, and ampacity tables (Article 400)Switch installation, ratings, grounding, and accessibility requirements (Article 404)Industrial control panel conductor sizing, overcurrent protection, short-circuit current rating, and marking (Article 409)Article 430 - Motors, Motor Circuits, and Controllers
2017 National Electrical Code, NFPA Calculations
1 Q · 2%
Motor branch-circuit conductor ampacity calculations (Article 430.22, 430.24)Motor branch-circuit short-circuit and ground-fault protective device ratings (Table 430.52)Motor overload protection sizing and trip current percentages (Article 430.32)Full-load current determination from NEC motor tables (Tables 430.247–430.250)Feeder conductor ampacity and protective device ratings for multiple motors (Articles 430.24, 430.62)Branch-circuit and feeder load calculations for general lighting and occupancy loads (Article 220, Table 220.12)Demand factors for feeder and service load calculations (Tables 220.42, 220.54, 220.55, 220.84)Conduit fill calculations using Chapter 9 tables (Table 1, Table 4, Table 5)Article 430 - Motors, Motor Circuits, and Controllers
Key Distinctions
Hard conversionvsSoft conversion
Hard conversion changes the dimensions or properties of the item into new sizes, while soft conversion is a direct mathematical conversion that changes the description of a measurement but not the actual dimension; NEC 90.9(C) requires hard conversion except in four listed cases (trade size designators, extracted material, industry practice, and where a negative impact on safety would result) where soft conversion is permitted/required.
NEC 2017 Section 90.9(C)(1)Wye-start, delta-run motor conductors (430.22(C))vsPart-winding connected motor conductors (430.22(D))
Conductors between controller and motor must be not less than 72 percent of motor full-load current for wye-start, delta-run (58% × 1.25), but not less than 62.5 percent for part-winding connected motors (50% × 1.25).
NEC 2017 Section 430.22(C)Overload device max at 115% of nameplate FLCvsOverload device max at 125% of nameplate FLC
Under 430.32(A)(1) a separate overload device is rated/set at not more than 125% of nameplate full-load current for motors marked with a service factor of 1.15 or greater or a temperature rise of 40°C or less, and not more than 115% for all other motors — two separate maximums, not a range.
NEC 2017 Section 430.32(A)(1), 430.32(C)Motor outlet branch-circuit loadvsGeneral-use receptacle outlet load
A motor outlet load is calculated per 430.22 at 125 percent of the motor full-load current, while general-use receptacle outlets are calculated at not less than 180 VA per single or multiple receptacle on one yoke under 220.14(I).
NEC 2017 Section 220.14(C) and Section 430.22NEC 240.4(B) next higher standard ratingvsNEC 240.4(C) devices rated over 800 amperes
The next higher standard overcurrent device rating above conductor ampacity is permitted only where the selected rating does not exceed 800 amperes; where the device is rated over 800 amperes, the conductor ampacity must be equal to or greater than the device rating.
NEC 2017 Section 240.4(B)Short-Circuit Current RatingvsInterrupting Rating
Short-circuit current rating is the prospective symmetrical fault current at a nominal voltage to which an apparatus or system can be connected without sustaining damage exceeding defined acceptance criteria, while interrupting rating is the highest current at rated voltage a device is identified to interrupt under standard test conditions.
NEC 2017 Article 100 (Definition: Short-Circuit Current Rating)SPD Type 1vsSPD Type 2
Type 1 is permanently connected between the secondary of the service transformer and the line side of the service disconnect overcurrent device; Type 2 is permanently connected on the load side of the service disconnect overcurrent device, including at a branch panel (Type 3 is point-of-utilization, Type 4 is component SPDs).
NEC 2017 Article 100 (Definition: Surge-Protective Device (SPD))Cables marked by printed tag (310.120(B)(3))vsCables surface marked (310.120(B)(1))
Type MI cable, switchboard wires, metal-covered single-conductor cables, and Type AC cable are tag marked on the coil, reel, or carton, whereas nonmetallic-sheathed cable, underground feeder and branch-circuit cable, and power-limited tray cable are surface marked.
NEC 2017 Section 310.120(B)(3)Multifamily dwellingvsTwo-family dwelling
Article 100 defines a multifamily dwelling as a building containing three or more dwelling units; a building with exactly two units is a two-family dwelling.
NEC 2017 Article 100 (Definition: Dwelling, Multifamily)Transformer secondary conductors protected by primary OCPDvsSecondary conductors NOT protected by primary OCPD (240.4(F))
2-wire single-phase and delta-delta 3-wire secondaries are permitted to be protected by the primary-side device, but single-phase (other than 2-wire) and multiphase (other than delta-delta, 3-wire) secondary conductors shall not be considered protected by the primary overcurrent protective device.
NEC 2017 Section 240.4(F)Feeder sizing for several motors (430.24)vsBranch-circuit sizing for a single motor (430.22)
A feeder is sized at 125% of the full-load current of only the highest rated motor plus 100% of the full-load currents of all other motors plus non-motor loads, while a single continuous-duty motor branch circuit is sized at 125% of that motor's full-load current.
NEC 2017 Section 430.24Supplementary overcurrent protection (240.10)vsRequired branch-circuit overcurrent devices
Supplementary overcurrent protection shall not be used as a substitute for required branch-circuit overcurrent devices or in place of required branch-circuit protection.
NEC 2017 Section 240.10Instantaneous trip breaker for Design B energy-efficient squirrel cage motorvsInstantaneous trip breaker for 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 800% for other AC polyphase motor types.
NEC 2017 Table 430.52Key Terms
Ampacity NEC 2017
The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating (Article 100).
Continuous Load NEC 2017 Article 100
A load where the maximum current is expected to continue for 3 hours or more (Article 100).
Authority Having Jurisdiction (AHJ) NEC 2017 Article 100 (Definitions)
An organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure; per 90.4 the AHJ makes interpretations of the rules, decides on approval of equipment and materials, and grants special permission.
Short-Circuit Current Rating NEC 2017 Article 100 (Definition: Short-Circuit Current Rating)
The prospective symmetrical fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria (Article 100).
Dwelling, Multifamily NEC 2017 Article 100 (Definition: Dwelling, Multifamily)
A building that contains three or more dwelling units (Article 100).
Effective ground-fault current path NEC 2017 Section 250.4(A)(5)
A low-impedance circuit capable of safely carrying the maximum ground-fault current back to the electrical supply source to facilitate operation of the overcurrent device; per 250.4(A)(5) the earth shall not be considered an effective ground-fault current 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.
Trade size designator NEC 2017 Section 90.9(C)(1)
A size designation used where the actual measured size of a product is not the same as the nominal size; 90.9(C)(1) permits soft conversion for trade sizes and trade practices are followed.
Grounded conductor identification, 6 AWG or smaller (200.6(A)) NEC 2017 Section 200.6(A)
An insulated grounded conductor 6 AWG or smaller shall be 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.
Bonding jumper installed outside a raceway (250.102(E)(2)) NEC 2017 Section 250.102(E)(2)
A bonding jumper or equipment bonding jumper installed on the outside shall be routed with the raceway or enclosure and shall not exceed 1.8 m (6 ft), with an exception allowing greater lengths at outside pole locations.
Supplemental rod electrode spacing (250.53(A)(3)) NEC 2017 Section 250.53(A)(3)
Where multiple rod, pipe, or plate electrodes are installed to meet that section, they shall not be less than 1.8 m (6 ft) apart.
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.
Adjustable-trip circuit breaker rating (240.6(B)) NEC 2017
Where the breaker has external means for adjusting the long-time pickup current setting and does not meet 240.6(C) for restricted access, its rating is the maximum setting possible.
Standard ampere ratings (Table 240.6(A)) NEC 2017 Table 240.6(A)
Standard ratings for fuses and inverse time circuit breakers include values such as 45, 70, and 110 amperes; 85 amperes is not a standard rating listed in the table.
Thermal relays and similar devices (240.9) NEC 2017 Section 240.9
Devices not designed to open short circuits or ground faults shall not be used to protect conductors against overcurrent due to short circuits or ground faults, but are permitted to protect motor branch-circuit conductors from overload where protected in accordance with 430.40.
Coordination system under 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 shall be permitted.
Motor full-load current values (430.6(A)(1)) NEC 2017 Section 430.6(A)(1)
For general motor applications — other than motors built for low speeds (less than 1200 RPM) or high torques and multispeed motors, for which the nameplate current ratings must be used — the values in Tables 430.247 through 430.250, not the motor nameplate current rating, are used to determine conductor ampacity and ampere ratings of switches and branch-circuit short-circuit and ground-fault protection; separate motor overload protection is still based on the motor nameplate current rating per 430.6(A)(2).
Mechanical execution of work (110.12(A)) NEC 2017 Section 110.12(A)
Unused openings in boxes, raceways, and enclosures — other than those intended 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.
Formulas to Know
Branch-circuit conductor ampacity for a single continuous-duty motor
Minimum conductor ampacity = 1.25 × motor full-load current rating (FLC taken from Tables 430.247–430.250 per 430.6(A)(1)); i.e., not less than 125%.Controller-to-motor conductors, wye-start delta-run motor
Not less than 72% of motor FLC (58% of load current × 1.25).Controller-to-motor conductors, part-winding connected motor
Not less than 62.5% of motor FLC (50% × 1.25); line-side conductors still sized at 125% of FLC.Feeder conductors supplying several motors (430.24)
Ampacity not less than 125% of the FLC of the HIGHEST rated motor + sum of FLC of all OTHER motors (100%) + non-motor loads.Maximum rating/trip setting of a separate motor overload device (430.32(A)(1))
Max = 1.25 × nameplate FLC for motors marked service factor ≥1.15 or temperature rise ≤40°C; Max = 1.15 × nameplate FLC for all other motors. Worked example (30 A nameplate): no marking → 30 × 1.15 = 34.5 A; SF 1.15 → 30 × 1.25 = 37.5 A. These are maximums; lower settings comply. Only if insufficient to start the motor or carry the load does 430.32(C) permit up to 130% or 140%.Inverse time circuit breaker for motor branch-circuit short-circuit/ground-fault protection
Table 430.52(C)(1) maximum = 250% of motor FLC; where the motor fails to start at that rating, Exception No. 2 permits an increase that shall in no case exceed 400% of FLC for motors of 100 A or less (300% above 100 A). Worked examples: 50 A FLC → 50 × 2.5 = 125 A standard size, cap 50 × 4 = 200 A; 60 A FLC → 60 × 4 = 240 A maximum.Part-winding start induction motor, each winding connection (430.4)
Branch-circuit short-circuit and ground-fault protection for each motor-winding connection = not more than one-half the value specified by 430.52.Minimum bending radius, Type MC cable with interlocked armor or corrugated sheath (330.24(B))
Radius of inner edge = 7 × external diameter of the metallic sheath. Worked example: 1.5 in. diameter → 7 × 1.5 = 10.5 in.Dwelling general lighting, small-appliance and laundry load (Article 220 / Table 220.12)
Total VA = (floor area in sq ft × 3 VA/sq ft) + (1,500 VA × number of small-appliance circuits) + (1,500 VA × number of laundry circuits). Worked examples: 2,000 sq ft, 2 SA, 1 laundry = 6,000 + 3,000 + 1,500 = 10,500 VA; 1,800 sq ft, 3 SA, 2 laundry = 5,400 + 4,500 + 3,000 = 12,900 VA; four units of 1,200 sq ft, 2 SA, 1 laundry each = 8,100 VA × 4 = 32,400 VA before demand factors.Box fill minimum volume (NEC 2020/2023/2026 Table 314.16(B))
Minimum volume = number of conductor allowances × 2.00 cu in. per 14 AWG conductor. Worked examples: Figure EB-1, 10 allowances × 2.00 = 20.00 cu in.; Figure EB-4, 12 allowances × 2.00 = 24.00 cu in.