Exam Cheat Sheet · Quick Reference

Idaho Limited Electrical Irrigation Sprinkler 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
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 (Article 90.1–90.2)Installations covered and not covered by the NECNEC code arrangement and chapter organization (Article 90.3)Authority having jurisdiction (AHJ) enforcement and special permissionMandatory vs. permissive rules and explanatory material (Article 90.5)Equipment examination, listing, and approval (Article 90.7)Wiring planning for future expansion and circuit limitations (Article 90.8)Units of measurement and SI/inch-pound dual system (Article 90.9)
2017 National Electrical Code, NFPA – Chapter 1 5 Q · 12%
Key NEC definitions and terminology (Article 100 Part I)Equipment approval, listing, and labeling requirementsElectrical connections, splices, and conductor temperature ratingsWorking space and clearances around electrical equipmentGuarding of live parts and enclosure type selectionEquipment marking, arc-flash hazard warnings, and disconnecting means identificationWiring integrity, wiring methods, and conductor materials and sizesArticle 100 - DefinitionsArticle 110 - Requirements for Electrical Installations
2017 National Electrical Code, NFPA – Chapter 2 11 Q · 28%
Grounding and bonding requirements for electrical systems and equipment (Article 250)Grounding electrode system types, installation, and sizingEquipment grounding conductor types, sizing, and identificationBonding methods for services, piping systems, and structural metalBranch circuit ratings, conductor sizing, and overcurrent protection (Article 210)Branch-circuit, feeder, and service load calculations (Article 220)Overcurrent protection devices, ratings, and locations (Article 240)Outside branch circuits and feeders — clearances, disconnecting means, and conductor requirements (Article 225)Article 250 - Grounding and Bonding
2017 National Electrical Code, NFPA – Chapter 3 5 Q · 12%
Underground installation requirements and minimum burial depths (Table 300.5)Conductor ampacity tables and temperature correction/adjustment factors (Article 310)Wiring methods for conduit types: EMT, RMC, IMC, PVC, FMC, LFMC, and LFNCType UF and Type USE cable uses permitted and installation requirementsOutlet, junction, and pull box sizing and installation (Article 314)Protection of conductors and raceways against physical damage (300.4)Conductor identification, marking, and insulation types (310.104, 310.120)Cabinets and enclosures: wire-bending space, conductor deflection, and spacing requirements (Article 312)Article 310 - Conductors for General Wiring
2017 National Electrical Code, NFPA – Chapter 6 16 Q · 40%
Irrigation cable construction requirements and installation standardsDisconnecting means requirements for irrigation machinesEquivalent current ratings for intermittent-duty irrigation machinesGrounding and bonding requirements for irrigation equipmentCollector ring ratings and protectionSeveral motors on one branch circuit — protection and tap requirementsCenter pivot irrigation machine equivalent current ratingsMain control panel marking requirements

Key Distinctions

Soft conversionvsHard conversion

Soft conversion is a direct mathematical conversion that does not change the actual dimension and shall be used where a negative impact on safety would result; hard conversion changes dimensions or properties into new sizes.

NEC 2017 Section 90.9(C)(4)
675.7(A) equivalent continuous-current rating (irrigation machine with inherent intermittent duty, not center pivot)vs675.22(A) equivalent continuous-current rating (center pivot machine)

675.7(A) adds the remaining motors' nameplate full-load currents multiplied by their maximum percent duty cycle to 125% of the largest motor, while 675.22(A) adds 60% of the sum of the remaining motors to 125% of the largest motor.

NEC 2017 Section 675.7(A)
675.7(B) equivalent locked-rotor current (non-center-pivot intermittent duty machine)vs675.22(B) equivalent locked-rotor current (center pivot machine)

675.7(B) uses the numerical sum of the locked-rotor currents of the two largest motors plus 100% of the nameplate full-load currents of all remaining motors; 675.22(B) uses two times the locked-rotor current of the largest motor plus 80% of the sum of the full-load currents of the remaining motors.

NEC 2017 Section 675.7(B)
675.11(A) collector rings transmitting current for power purposesvs675.11(B) collector rings for control and signal purposes

Both are rated at not less than 125% of the full-load current of the largest device served plus the full-load current of all other devices — (A) applies to power-transmitting rings and (B) applies to control and signal rings; the grounding collector ring under 675.11(C) is rated not less than the value sized by 675.11(A).

NEC 2017 Section 675.11(A)
Main bonding jumpervsSystem bonding jumper

The main bonding jumper is the connection between the grounded circuit conductor and the equipment grounding conductor at the service; the system bonding jumper serves a similar function at a separately derived system.

NEC 2017 Article 100 (Definition: Bonding Jumper, Main)
Insulated conductorvsCovered conductor

An insulated conductor is encased within material of composition and thickness recognized by the Code as electrical insulation; a covered conductor is encased in material not recognized as electrical insulation.

NEC 2017 Article 100 (Conductor, Insulated)
THHNvsWet-location conductor types (MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THWN, THWN-2, XHHW, XHHW-2, ZW)

Per 310.10(C) the listed types are permitted in wet locations, while THHN is a 90°C dry-and-damp-location insulation only (Table 310.104(A)) and is not permitted in wet locations such as an underground raceway.

NEC 2017 Section 310.10(C)
240.4(B) next higher standard overcurrent device ratingvs240.4(C) overcurrent device rated over 800 amperes

240.4(B) permits the next higher standard rating above conductor ampacity only when that selected rating does not exceed 800 amperes; where the device is rated over 800 amperes, 240.4(C) requires conductor ampacity to be equal to or greater than the device rating.

NEC 2017 Section 240.4(B)
Supplementary overcurrent protectionvsRequired branch-circuit overcurrent device

Per 240.10, supplementary overcurrent protection shall not be used as a substitute for required branch-circuit overcurrent devices or in place of the required branch-circuit protection.

NEC 2017 Section 240.10
NEC Chapters 1, 2, 3, and 4vsNEC Chapters 5, 6, 7 and Chapter 8

Per 90.3, Chapters 1 through 4 apply generally to all electrical installations, Chapters 5, 6, and 7 apply to special occupancies, special equipment, or other special conditions and may supplement or modify Chapters 1 through 7, and Chapter 8 (communications systems) is independent except where specifically referenced.

NEC 2017 Section 90.3
Informational notes / explanatory materialvsCode requirements

Per 90.5(C), informational notes are included for informational purposes only and are not enforceable as requirements of the Code.

NEC 2017 Section 90.5(C)
180 VA per receptacle outlet (one yoke)vs90 VA per receptacle for a single piece of equipment with four or more receptacles

Per 220.14(I), each single or multiple receptacle on one yoke is calculated at not less than 180 volt-amperes, but a single piece of equipment consisting of a multiple receptacle comprised of four or more receptacles is calculated at not less than 90 volt-amperes per receptacle.

NEC 2017 Section 220.14(I)
210.23(A)(2) fastened-in-place utilization equipment limitvs210.23(A)(1) cord-and-plug-connected equipment not fastened in place limit

Where lighting units or cord-and-plug-connected equipment not fastened in place are also supplied, fastened-in-place utilization equipment (other than luminaires) shall not exceed 50% of the branch-circuit rating, whereas a single cord-and-plug-connected appliance not fastened in place is limited to 80% of the branch-circuit rating.

NEC 2017 Section 210.23(A)(2)
Transformer 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) secondary conductors shall not be considered protected by the primary overcurrent protective device.

NEC 2017 Section 240.4(F)

Key Terms

Ampacity (Article 100) NEC 2017
The maximum current, in amperes, that 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, which drives the 125 percent sizing rules elsewhere in the Code.
Authority Having Jurisdiction (AHJ) (Article 100; 90.4) 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.
Center Pivot Irrigation Machine (675.2) NEC 2017 Section 675.2
A multimotored irrigation machine that revolves around a central pivot and employs alignment switches or similar devices to control the individual motors, which triggers the Part II equivalent-current rules of 675.22.
Irrigation machine main disconnecting means (675.8(B)) NEC 2017 Section 675.8(B)
The disconnect that must provide overcurrent protection, be located at the point of connection of electric power to the machine or in sight from the machine, and be readily accessible and lockable in accordance with 110.25.
Effective ground-fault current path (250.4(A)(3) and (A)(5)) NEC 2017 Section 250.4(A)(3)
A low-impedance circuit established by connecting non-current-carrying conductive materials together and to the electrical supply source, capable of safely carrying maximum ground-fault current to facilitate operation of the overcurrent device; the earth shall not be considered an effective ground-fault current path.
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.
Adjustable-trip circuit breaker rating (240.6(B)) NEC 2017
Where the breaker has external means for adjusting the current (long-time pickup) setting and does not meet 240.6(C) for restricted access, its ampere rating shall be 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 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.
Thermal relays and similar devices (240.9) NEC 2017 Section 240.9
Devices not designed to open short circuits or ground faults shall not protect conductors against short-circuit or ground-fault overcurrent, but are permitted to protect motor branch-circuit conductors from overload where protected in accordance with 430.40.
Mechanical execution of work — unused openings (110.12(A)) NEC 2017 Section 110.12(A)
Unused openings, other than those intended for equipment operation or mounting or permitted as part of listed equipment design, shall be effectively closed to afford protection substantially equivalent to the wall of the equipment.
Voltage considered (110.4) NEC 2017 Section 110.4
Throughout the Code the voltage considered shall be that at which the circuit operates, and equipment voltage rating shall not be less than the nominal circuit voltage.
Conductor size expression (110.6) NEC 2017 Section 110.6
Conductor sizes are expressed in American Wire Gage (AWG) or in circular mils — AWG up to 4/0, circular mils (kcmil) for larger than 4/0.
PVC expansion fittings (352.44) NEC 2017 Section 352.44
Expansion fittings shall be provided to compensate for thermal expansion and contraction where the expected length change is 6 mm (¼ in.) or greater in a straight run between securely mounted items.
FMC where flexibility is necessary (348.60) NEC 2017
Where FMC connects equipment to minimize vibration transmission or to allow movement after installation, an equipment grounding conductor shall be installed.
Scope of the Code (90.2(A)) NEC 2017
Covers the installation and removal of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and raceways; and optical fiber cables and raceways for public and private premises including buildings, structures, mobile homes, recreational vehicles, and floating buildings.

Formulas to Know

Equivalent continuous-current rating — irrigation machine with inherent intermittent duty, NOT a center pivot (675.7(A)), for branch-circuit conductors and overcurrent protection(1.25 × largest motor nameplate FLC) + (sum of remaining motors' nameplate FLC × maximum percent duty cycle). Examples: (1.25×10)+(16×0.50)=20.5 A; (1.25×10)+(20×0.50)=22.5 A; (1.25×16)+(20×0.50)=30 A; (1.25×20)+(18×0.50)=34 A
Equivalent continuous-current rating — center pivot irrigation machine (675.22(A)); also the minimum rating for the main controller per 675.8(A)(1)(1.25 × largest motor nameplate FLC) + (0.60 × sum of remaining motors' nameplate FLC). Examples: (1.25×12)+(0.60×30)=33 A; (1.25×16)+(0.60×25)=35 A; (1.25×14)+(0.60×31.5)=36.4 A; (1.25×15)+(0.60×12)=25.95 A
Equivalent locked-rotor current — irrigation machine with inherent intermittent duty, NOT a center pivot (675.7(B))LRC of largest motor + LRC of second-largest motor + 100% of the sum of the nameplate FULL-LOAD currents of all remaining motors (not their locked-rotor currents). Examples: 60+48+(3×6)=126 A; 90+72+(3×8)=186 A
Equivalent locked-rotor current — center pivot machine (675.22(B)), for main controller and disconnecting means(2 × locked-rotor current of largest motor) + (0.80 × sum of full-load currents of remaining motors). Example: (2×60)+(0.80×40)=152 A
Minimum rating of collector rings transmitting current for power purposes (675.11(A)); the grounding collector ring (675.11(C)) is rated not less than this same value(1.25 × full-load current of largest device served) + (full-load current of all other devices served). Examples: (1.25×16)+(3×8)=44 A; (1.25×16)+(4×7)=48 A
Minimum rating of collector rings for control and signal purposes (675.11(B))(1.25 × full-load current of largest device served) + (full-load current of all other devices). Example: (1.25×8)+3+2+2=17 A
Maximum rating of fastened-in-place utilization equipment on a multiple-outlet branch circuit also supplying lighting or non-fastened cord-and-plug equipment (210.23(A)(2))Total rating shall not exceed 50% of branch-circuit ampere rating. Example: 50% × 20 A = 10 A
Total conductor cross-sectional area for a conduit run (Chapter 9, Table 5; Note 3 includes the EGC at its actual area)Sum of (number of conductors × area per conductor from Table 5). Example: 7×0.0211 + 3×0.0133 + 1×0.0133 = 0.201 sq in
Conduit sizing for exactly two conductors (Chapter 9, Table 1 — 31% column)Total conductor area must fit within 31% of raceway area. Examples: two 10 AWG THHN = 2×0.0211 = 0.042 sq in → smallest EMT whose 31% area (0.094 sq in) is at least that is ½ in; two 4/0 AWG THHN = 2×0.3237 = 0.647 sq in → 2 in EMT (31% = 1.040 sq in)
Maximum number of conductors over 2 in a raceway (Chapter 9, Table 1 40% column, Table 4, Table 5 and Note 7 rounding)Number = 40% raceway area ÷ area per conductor; a resulting decimal of 0.8 or larger rounds up, below 0.8 is dropped. Example: 1 in EMT 40% = 0.346 sq in ÷ 0.0366 sq in (8 AWG THHN) = 9.45 → 9 conductors
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