Idaho Low Voltage Practice cheat sheet

Article 100 definitions govern throughout the Code: "listed" means equipment included in a list published by an approved testing laboratory; "labeled" means marked with that listing mark.

NEC Article 90 explains that the Code is not a design manual or instruction book for untrained persons; it is practical safeguarding of persons and property from electrical hazards.

Chapter 1 through 4 apply generally; Chapters 5, 6, and 7 modify or supplement them; Chapter 8 (communications) is independent except where it references other chapters, and Chapter 9 contains tables.

110.3(B) requires listed or labeled equipment to be installed and used in accordance with any instructions included in the listing or labeling.

Working space per 110.26: 30 in. wide, 36 in. deep (condition-dependent), 6 ft 6 in. high, and clear from floor to ceiling; depth increases with voltage and conditions.

110.26(C) requires at least one entrance of sufficient area to the working space; equipment rated 1200 A or more with overcurrent devices over 6 ft wide needs one entrance at each end.

110.27 requires guarding of live parts operating at 50 V or more where accessible; 110.34 sets working space for equipment over 1000 V.

Article 100: "overcurrent" is any current in excess of the rated current of equipment or the ampacity of a conductor; it may result from overload, short circuit, or ground fault.

110.14 covers electrical connections: terminals must be identified for the conductor material, and conductor ampacity is limited by terminal temperature ratings unless the equipment is listed otherwise.

Chapter 3 wiring methods are selected by occupancy and location; NM cable (Article 334) is limited to normally dry locations and is prohibited in commercial garages, theaters, and hazardous locations.

MC cable (Article 330) may be used in dry, damp, or wet locations where listed for those locations; interlocked armor provides a ground path but a separate equipment grounding conductor is often required.

EMT (Article 358) requires listed fittings; supports are required within 3 ft of boxes and every 10 ft, and EMT is not permitted where subject to severe physical damage unless protected.

RMC (Article 344) may be used in all occupancies and locations, including underground and hazardous locations where permitted; supports within 3 ft of termination and every 10 ft.

PVC conduit (Article 352) expansion fittings are required where the conduit changes temperature significantly; supports are spaced per Table 352.30 based on conduit size.

Liquidtight flexible metal conduit (Article 350) requires a separate equipment grounding conductor when flexibility is needed; LFMC is limited to 6 ft in lengths where used as a ground return path.

Cable trays (Article 392) require conductors to be supported and secured; ampacity adjustments apply where cables or conductors are stacked, per 392.80.

Conductors in parallel (310.10(H)) must be 1/0 AWG or larger, identical in length, material, size, insulation, and terminated in the same manner.

Article 725 covers Class 1, Class 2, and Class 3 remote-control and signaling circuits; Class 2 and 3 circuits are power-limited and separated from power conductors unless using a Chapter 9 Table 5 or 800.133 separation method.

Article 800 covers communications circuits (telephone, CATV, network); 800.133 requires 2 in. separation from power conductors unless a barrier or other approved method is used.

Article 820 covers community antenna television and radio distribution; Article 830 covers network-powered broadband communications.

Class 2 circuits are limited to 30 V and 100 VA or less; Class 3 circuits may operate up to 150 V and are limited to 100 VA; Class 1 is not power-limited.

Article 760 covers fire alarm systems; power-limited fire alarm circuits (PLFA) are separated from Class 1 and power conductors per 760.130.

Article 770 covers optical fiber cables; nonconductive fiber does not require grounding, but conductive fiber cable armor must be bonded per 770.100.

Article 840 covers premises-powered broadband communications; 840.160 requires a listed primary protector and grounding for the communications system.

Low voltage lighting systems operating at 30 V or less are covered in Article 411; the system must be listed and supplied by a Class 2 power source.

Article 250: the grounding electrode system includes a metal underground water pipe (25 ohms or less, 10 ft in contact with soil), metal frame of a building, concrete-encased electrode (20 ft of 1/2 in. rebar or 4 AWG bare copper), and ground ring.

250.53(D)(2) requires a supplemental electrode where the water pipe is the only electrode; the water pipe must be supplemented by another electrode.

250.66 sizes the grounding electrode conductor based on the largest service-entrance conductor; Table 250.66 gives sizes (e.g., 2 AWG copper service → 8 AWG copper GEC).

250.122 sizes the equipment grounding conductor based on the rating of the overcurrent device protecting the circuit; Table 250.122 gives minimum sizes (e.g., 20 A → 12 AWG copper; 100 A → 8 AWG copper).

250.52(A)(3) concrete-encased electrode: at least 20 ft of 1/2 in. or larger reinforcing steel or 4 AWG bare copper in the footing; it is the preferred electrode for new construction.

250.32 requires a grounding electrode at separate buildings or structures supplied by a feeder; an equipment grounding conductor must be run with the feeder.

Bonding jumpers around water meters, gas piping, and other removable components must be sized per 250.102; gas piping bonding is required by 250.104(B).

250.4 describes performance: grounded systems must limit voltage to ground and facilitate overcurrent device operation; equipment must be bonded to provide a low-impedance fault path.

Article 310 and Table 310.16 give ampacities for conductors; the 60°C column applies to circuits rated 100 A or less unless terminals are listed for higher temperatures.

Ampacity adjustment: Table 310.15(C)(1) reduces ampacity for more than three current-carrying conductors in a raceway or cable (80% for 4–6, 70% for 7–9).

Table 310.15(B)(2)(a) ambient temperature correction factors apply to conductors in high-temperature environments (e.g., 0.82 at 40°C for 60°C insulation).

240.4(D) small conductor rule: 14 AWG copper limited to 15 A, 12 AWG to 20 A, 10 AWG to 30 A, unless specific exceptions apply.

240.4(B) next-size-up rule: if the conductor ampacity does not match a standard OCPD rating, the next higher standard rating may be used if it does not exceed 800 A and the conductor is not part of a multioutlet branch circuit.

Table 240.6(A) standard ampere ratings: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200 A.

Voltage drop: 210.19(A) informational note recommends 3% maximum on branch circuits and 5% total; use VD = 2 × K × I × L / CM for single-phase.

210.20(A) requires the branch-circuit overcurrent device rating to be at least 125% of the continuous load plus 100% of the noncontinuous load.

314.16 box fill: count each conductor entering the box; 14 AWG = 2.00 cu in., 12 AWG = 2.25 cu in., 10 AWG = 2.50 cu in. per conductor; each device yoke counts as two conductors of the largest size.

314.16(B)(1): each conductor that originates outside and terminates inside counts once; conductors passing through without splice count once; grounding conductors count once total based on the largest.

314.28 pull box sizing: for straight pulls, the box length must be at least 8 times the trade size of the largest raceway; for angle pulls, 6 times the largest raceway plus the sum of the other raceways on the same side.

314.29 requires boxes and conduit bodies to be accessible without removing building finish; 314.30 requires handhole enclosures to be listed and accessible.

300.14 requires at least 6 in. of free conductor at each outlet, junction, or switch point, with 3 in. extending outside the opening.

300.4 requires protection against physical damage: where raceways or cables are less than 1 1/4 in. from the edge of framing members, steel plates or bushings must be installed.

300.5 burial depths: direct-buried cables and raceways require 24 in. for direct burial, 18 in. for residential branch circuits at 120 V or less with GFCI protection, and 6 in. under a concrete slab.

Article 314: boxes must be supported; 314.23 lists support methods including structural mounting, and 314.20 requires flush boxes to be set so the box extends at least 1/4 in. beyond the finished surface.

Article 500 and 505 define hazardous locations: Class I (flammable gases/vapors), Class II (combustible dust), Class III (fibers/flyings); Divisions or Zones further classify the risk.

Article 511 commercial garages: areas within 18 in. of the floor are Class I, Division 2; low-voltage and communications wiring must comply with the classified area rules.

Article 517 health care facilities: patient care areas require redundant grounding and isolated power systems in critical care (Category 1) spaces; low-voltage cabling must not be installed in patient care vicinity without approval.

Article 547 agricultural buildings: equipotential planes are required at concrete slabs and metal equipment; wiring methods must resist dust, water, and corrosion.

Article 680 swimming pools: low-voltage lighting must be listed for pool use and supplied by a Class 2 transformer; equipotential bonding is required around the pool perimeter.

Article 690 solar photovoltaic systems: Article 690 applies to PV circuits; voltage calculations must use the module's temperature-corrected open-circuit voltage.

Article 725 and 760 apply in special occupancies where fire alarm and signaling circuits are installed; separation and survivability requirements vary by occupancy.

Article 550 mobile homes and 551 recreational vehicles: low-voltage wiring must use listed materials and be protected from physical damage; 550.18 requires grounding of the frame.

Idaho regulates electrical contractors and journeyman/master electricians through the Idaho Division of Occupational and Professional Licenses (DOPL), Idaho Electrical Board.

Idaho law requires an electrical contractor license to engage in the business of electrical contracting; a licensed master or journeyman electrician must supervise work.

Idaho requires a master electrician to hold the contractor license or be the qualifying licensee; the contractor license is issued to a business entity with a designated responsible licensee.

Low-voltage work in Idaho is generally exempt from journeyman licensing when it is limited to communications, alarm, or data cabling, but local jurisdictions may impose additional permit requirements.

Idaho requires permits and inspections for electrical work; local building departments issue permits and conduct inspections under adopted codes (often the current NEC with Idaho amendments).

Idaho continuing education: licensees must complete continuing education hours per the Idaho Electrical Board rules to renew; renewal cycles and hour requirements are set by DOPL rule.

Unlicensed electrical contracting in Idaho is subject to civil penalties and possible criminal enforcement; contractors must display the license number on advertising and vehicles.

Idaho adopts the NEC by reference through the Idaho Electrical Code with state amendments; the adopted edition and amendments are published by DOPL.

OSHA 29 CFR 1910 Subpart S and 1926 Subpart K govern electrical safety; lockout/tagout (1910.147) is required before working on energized equipment.

NFPA 70E establishes arc flash and shock protection boundaries; approach boundaries depend on voltage and available fault current, and PPE is selected by incident energy.

Test before touch: verify absence of voltage with a properly rated meter, and treat all conductors as energized until tested and grounded.

GFCI protection is required for temporary receptacles on construction sites per 590.6; all 125 V, 15–20 A receptacles must have GFCI protection.

Ladder safety: maintain a 4:1 angle, three points of contact, and keep ladders at least 10 ft from energized overhead lines up to 50 kV.

Hand tools must be insulated for the voltage involved; use a noncontact voltage tester as a first check and a solenoid or digital meter for confirmation.

Confined space entry requires atmospheric testing and a rescue plan; electrical work in wet locations requires additional GFCI and insulated tool precautions.

First aid for electrical shock: do not touch the victim until the source is de-energized; call 911 and begin CPR if trained; report all shocks and near misses.

Ohm's law: V = I × R; power: P = V × I = I²R = V²/R. Use these to calculate load current and voltage drop.

Single-phase voltage drop: VD = 2 × K × I × L / CM, where K = 12.9 for copper and 21.2 for aluminum, L in feet, CM = circular mils.

Three-phase voltage drop: VD = 1.732 × K × I × L / CM; three-phase power: P = 1.732 × V × I × PF.

Circular mils: CM = (diameter in mils)²; 1 mil = 0.001 in.; 1,000 circular mils = 1 kcmil; 1 AWG = 1 mil diameter, 2 AWG = 2 mil diameter, etc.

Ampacity adjustment example: 6 current-carrying 12 AWG THHN conductors in a raceway at 30°C → 30 A × 0.80 = 24 A, then apply any ambient correction.

Series circuits: same current through all components, total resistance is the sum; parallel circuits: same voltage across branches, total resistance is the reciprocal sum.

Power factor: true power (W) = apparent power (VA) × PF; for resistive loads PF = 1, so VA equals watts.

Box fill example: a box with four 12 AWG conductors, one device (two conductor equivalents), and one ground → 7 × 2.25 = 15.75 cu in. minimum box volume.

Article 100 defines "accessible" as admitting close approach and "readily accessible" as capable of being reached quickly without climbing or removing obstacles.

Article 100: "continuous load" is a load expected to continue for 3 hours or more; "duty cycle" and "noncontinuous load" are also defined there.

90.4 allows the authority having jurisdiction (AHJ) to interpret the Code and to grant special permission for alternate methods where equivalent safety is provided.

110.12 requires electrical equipment to be installed in a neat and workmanlike manner; unused openings must be closed and equipment must be mechanically secure.

110.22 requires disconnecting means to be marked to indicate the purpose of the circuit; 110.24 requires available fault current marking at service equipment.

Article 100: "branch circuit" is the circuit conductors between the final overcurrent device and the outlet(s); "feeder" is between the service equipment and the final branch-circuit overcurrent device.

90.2(B) lists installations not covered by the Code, including ships, aircraft, railways, and utility-owned installations under exclusive utility control.

Article 100: "ground-fault circuit interrupter" is a device intended for protection of personnel that de-energizes a circuit within a set time when current to ground exceeds a threshold.

Article 300 general requirements apply to all wiring methods: conductors must be installed in raceways or cables listed for the purpose, and raceways must be continuous between boxes and fittings.

300.15 requires a box or conduit body at each splice, outlet, switch point, junction, and raceway termination; 300.17 requires raceways to be of adequate size for the conductors.

Article 320 armored cable (AC) and Article 330 metal-clad cable (MC) differ: MC has a larger bonding strip and may be used in wet locations where listed; AC is limited to dry locations.

Article 338 service-entrance cable (SE) and Article 340 underground feeder (UF) cable: UF is listed for direct burial and may be used in wet locations.

Article 342 intermediate metal conduit (IMC) and Article 344 rigid metal conduit (RMC) require threaded connections and are permitted in hazardous locations.

Article 358 EMT: minimum size is 1/2 in. trade size; bends must not exceed 360 degrees between boxes, and conduit must be reamed to remove burrs.

Article 362 electrical nonmetallic tubing (ENT) is limited to concealed locations in buildings not exceeding three floors above grade and is not permitted in hazardous locations.

Article 314.17 requires raceway entries into boxes to be made with fittings listed for the purpose; 300.10 requires metal raceways to be mechanically and electrically continuous.

Article 725 Class 1 circuits: power-limited Class 1 circuits are limited to 1000 VA and 30 V (or 600 V where the power source is limited); Class 1 circuits must be installed using Chapter 3 wiring methods.

725.121 requires Class 2 and Class 3 power sources to be listed; the power source must limit voltage and current to the Class 2 or 3 limits.

800.133(A) separation: communications cables must be separated from power conductors by at least 2 in., or by a barrier, or by a raceway, unless the power conductors are in a Chapter 3 raceway.

800.100 requires a listed primary protector for communications circuits entering a building; the protector must be grounded to the building grounding electrode system.

820.93 and 830.93 require grounding of the cable shield or messenger where present; 840.101 covers grounding of premises-powered broadband systems.

Article 760 fire alarm circuits: power-limited fire alarm circuits may share a raceway with Class 2 or 3 circuits only where all circuits are power-limited and the raceway is listed for the purpose.

Article 770 optical fiber: nonconductive fiber cables do not require grounding or bonding; conductive armor must be bonded to the equipment grounding conductor.

Article 411 low-voltage lighting: systems must be listed and supplied by a Class 2 power source; the output circuit must not exceed 30 V and must be installed per the listing instructions.

250.50 requires all grounding electrodes present at a building to be bonded together to form the grounding electrode system; 250.52 lists the permitted electrodes.

250.53(A)(2) requires a supplemental electrode where a single rod, pipe, or plate electrode has a resistance to ground greater than 25 ohms; 250.53(A)(3) requires the rod to be at least 8 ft long.

250.66 Table: service conductors of 2 AWG copper or smaller require an 8 AWG copper GEC; 1/0 copper requires 4 AWG; 3/0 copper requires 2 AWG; 350 kcmil copper requires 1/0 AWG.

250.122 Table: 15 A circuit → 14 AWG copper EGC; 20 A → 12 AWG; 30 A → 10 AWG; 60 A → 10 AWG; 100 A → 8 AWG; 200 A → 6 AWG; 400 A → 3 AWG.

250.104 requires metal water piping, metal gas piping, and other metal piping systems to be bonded to the grounding electrode system or to the equipment grounding conductor.

250.30 covers separately derived systems: the system bonding jumper must be installed at the source or first disconnecting means, and the grounded conductor must not be bonded again downstream.

250.148 requires the equipment grounding conductor to be connected to the box where circuit conductors are spliced; 250.146 covers receptacles and the grounding contact.

250.24(A) requires the service neutral to be bonded to the service equipment enclosure and the grounding electrode conductor at the service; 250.24(B) covers the main bonding jumper.

Table 310.16 ampacities for copper THHN at 30°C: 14 AWG = 25 A, 12 AWG = 30 A, 10 AWG = 40 A, 8 AWG = 55 A, 6 AWG = 75 A, 4 AWG = 95 A, 2 AWG = 130 A, 1/0 = 170 A, 250 kcmil = 290 A.

310.15(B)(1) ambient correction: for 30°C ambient, no correction; for 40°C ambient, 60°C insulation × 0.82, 75°C × 0.88, 90°C × 0.91.

430.52 motor branch-circuit short-circuit and ground-fault protection: inverse-time breaker sized up to 250% of motor full-load current, with the next-size-up permitted where the motor will not start.

430.22 motor branch-circuit conductors must be sized at 125% of the motor full-load current; 430.24 feeder conductors at 125% of the largest motor plus the sum of other loads.

210.19(A)(1) branch-circuit conductors must have an ampacity of at least 125% of the continuous load plus 100% of the noncontinuous load before adjustment.

240.21 tap rules: 10 ft taps require the tap conductor ampacity to be at least 1/10 of the overcurrent device rating and the tap to terminate in a single breaker; 25 ft taps require 1/3.

240.86 series-rated systems: the combination of overcurrent devices must be listed for the application, and the downstream device must be in a system tested and marked for series rating.

Table 250.122 and 240.4(D) interact: small conductors are limited by 240.4(D) unless the overcurrent device is listed for the conductor ampacity.

314.16(B)(2): each strap or yoke for a device counts as two conductors of the largest size in the box; a luminaire stud or hickey counts as one conductor of the largest size.

314.16(B)(3): one or more equipment grounding conductors count as a single conductor based on the largest size; 314.16(B)(4) counts cable clamps as one conductor.

314.28(A)(2) angle pulls: the distance from the raceway entry to the opposite wall must be at least 6 times the largest raceway trade size plus the sum of the diameters of the other raceways on the same side.

314.28(A)(3) U pulls: the distance between raceway entries must be at least 6 times the largest raceway trade size, and the opposite wall must be at least 6 times the largest size plus the other raceways.

300.5(D)(1) requires direct-buried conductors and cables to be protected from physical damage where they emerge from the ground, typically with a raceway or guard.

300.22(C) environmental air spaces: only metal raceways, metal-clad cable, or listed plenum-rated cable may be installed in a plenum; PVC and NM cable are prohibited.

314.25 requires a cover or faceplate on every box; 314.27 covers box support for luminaires and ceiling fans, with fan-rated boxes required for fans.

Article 376 and 378 metal wireways and nonmetallic wireways: conductors must be supported and secured, and wireways must be accessible; 376.22 limits conductor fill to 20% of the wireway area.

Article 501 Class I locations: Division 1 requires explosion-proof equipment; Division 2 permits equipment that is nonincendive or otherwise protected; sealing fittings are required at boundaries.

Article 502 Class II locations: dust-ignition-proof equipment and dust-tight enclosures are required; 502.10 lists permitted wiring methods including threaded rigid metal conduit.

Article 503 Class III locations: equipment must be dust-tight and minimize sparking; 503.10 permits rigid metal conduit, IMC, and listed flexible connections.

Article 514 motor fuel dispensing facilities: areas within 18 in. of the dispenser and the tank fill area are classified; low-voltage and communications equipment must comply with the classified area boundaries.

Article 517 patient care: 517.13 requires a redundant ground path (metal raceway plus insulated copper EGC) for receptacles in patient care areas; isolated power is required in critical care.

Article 680 pool bonding: 680.26 requires an equipotential bonding grid around the pool, including metal parts, and a bonding conductor of at least 8 AWG copper.

Article 690 PV: 690.7 requires maximum PV system voltage to be calculated using the lowest expected ambient temperature and the module's temperature coefficient of Voc.

Article 700 and 701 emergency and legally required standby systems: wiring must be separated from normal wiring and protected from fire damage; 700.10 covers fire protection of feeders.

Idaho Electrical Board rules define license categories: master electrician, journeyman electrician, apprentice, and electrical contractor; each has separate qualifications and renewal requirements.

Idaho requires an electrical contractor license for any person or business that contracts for electrical work; the contractor must designate a master electrician as the responsible licensee.

Idaho apprentice electricians must be registered with DOPL and work under the supervision of a licensed journeyman or master electrician; hour ratios are set by board rule.

Idaho requires a permit for electrical work except for minor repair or replacement work specifically exempted by the adopted code or local ordinance.

Idaho license renewal requires continuing education hours as set by DOPL rule; failure to complete CE can result in license lapse or reinstatement fees.

Idaho electrical contractors must carry general liability insurance and provide proof to DOPL; the board may require a surety bond for certain license types.

Idaho adopts the NEC by reference with state amendments; local jurisdictions may adopt more stringent requirements for permits and inspections.

Idaho law prohibits unlicensed contracting and provides for civil penalties; complaints are filed with DOPL and may result in fines or license revocation.

NFPA 70E Table 130.7(C)(15) provides arc flash PPE categories based on task and equipment; Category 1 requires arc-rated clothing with a minimum arc rating of 4 cal/cm².

OSHA 1926.403 requires electrical equipment to be approved for the purpose and installed per listing instructions; 1926.404 covers wiring design and protection on construction sites.

Lockout/tagout: isolate all energy sources, apply locks and tags, verify zero energy state, and release stored energy before work begins.

Temporary wiring on construction sites must be protected from physical damage, supported, and GFCI-protected; 590.4 covers supports and 590.6 covers GFCI.

Test instruments must be rated for the category of the circuit being tested (CAT III for distribution, CAT IV for service entrance); a CAT II meter must not be used on service equipment.

Overhead line clearance: keep all equipment and conductors at least 10 ft from energized lines up to 50 kV; increase clearance for higher voltages per OSHA Table S-5.

Personal protective equipment: hard hat, safety glasses, arc-rated clothing, insulated gloves rated for the voltage, and hearing protection where required.

Job-site housekeeping: keep work areas clear, store flammable materials properly, and maintain clear access to electrical panels and disconnects per 110.26.

Conductor resistance: R = ρL/A, where ρ is resistivity (copper ≈ 12.9 Ω·cmil/ft, aluminum ≈ 21.2 Ω·cmil/ft), L in feet, A in circular mils.

Load calculation: for a 120 V, 15 A circuit, maximum continuous load is 80% of 15 A = 12 A, or 1440 VA; the 125% rule applies to continuous loads.

Box fill example: 12 AWG conductor volume = 2.25 cu in.; a 4 × 4 × 1 1/2 in. box has 21 cu in., which allows nine 12 AWG conductors.

Transformer calculations: primary current = kVA × 1000 / primary voltage; secondary current = kVA × 1000 / secondary voltage; three-phase uses 1.732 in the denominator.

Conduit fill: Chapter 9 Table 1 limits raceway fill to 40% for three or more conductors; Table 4 gives the allowable area for each raceway size and type.

Power factor correction: kVAR = kW × (tan θ1 − tan θ2); capacitor kVAR is calculated from the initial and target power factor angles.

Series/parallel: for two resistors in parallel, R_total = (R1 × R2)/(R1 + R2); for three or more, use the reciprocal sum.

Motor full-load current: Table 430.250 gives FLC for three-phase motors (e.g., 10 HP at 230 V = 28 A); use 125% for conductor sizing.

Article 100: "fitting" is an accessory such as a locknut, bushing, or other part of a wiring system intended primarily to perform a mechanical rather than an electrical function.

Article 100: "outlet" is a point on the wiring system at which current is taken to supply utilization equipment; "receptacle" is a contact device installed at an outlet.

Article 100: "utilization equipment" is equipment that uses electrical energy for electronic, chemical, heating, lighting, or similar purposes.

110.9 requires equipment intended to interrupt current at fault levels to have an interrupting rating at nominal circuit voltage not less than the available fault current.

110.10 requires equipment to be capable of withstanding the let-through energy of the overcurrent protective device under fault conditions.

110.16 requires arc flash hazard warning labels on switchboards, panelboards, and motor control centers; the label must state the available fault current and clearing time.

Article 100: "service point" is the point of connection between the serving utility and the premises wiring; the service equipment is the necessary equipment, usually a switchboard or panelboard, connected to the load end of the service conductors.

90.5 mandates that the Code be used as a design specification only where it is complete and that the authority having jurisdiction may waive specific requirements where equivalent safety is provided.

Article 310.10 requires conductors to be insulated unless specifically permitted otherwise; 310.10(C) prohibits conductors of systems over 1000 V from occupying the same raceway as conductors of systems 1000 V or less unless separated.

310.6 requires conductors to be rated for the voltage and temperature of the circuit; 310.8 requires marking of conductors with the size, material, and insulation type.

Article 320 armored cable: the armor must be continuous and bonded; AC cable is not permitted in damp or wet locations unless listed for the purpose.

Article 334 NM cable: the cable must be secured within 12 in. of boxes and every 4 1/2 ft; NM cable is not permitted in raceways except for protection from physical damage.

Article 348 flexible metal conduit (FMC): permitted in dry locations and where flexibility is needed; a separate EGC is required where FMC is used with nonmetallic boxes.

Article 356 liquidtight flexible nonmetallic conduit (LFNC) is permitted in wet locations where listed; supports are required within 12 in. of boxes and every 3 ft.

Article 392 cable tray: conductors in tray must be supported at intervals not exceeding 3 ft for horizontal runs and 6 ft for vertical runs.

Article 358 EMT: 358.30 requires supports within 3 ft of boxes and every 10 ft; 358.24 requires bends to be made without damage to the conduit.

Article 725 Class 2 and Class 3 circuits must be installed in a Chapter 3 wiring method or as permitted by 725.135; cables must be listed for the purpose and marked with the circuit class.

725.136 requires separation of Class 2 and 3 conductors from power conductors by at least 2 in., or by a barrier, or by a raceway, unless the power conductors are in a Chapter 3 raceway.

800.24 requires communications cables to be supported at intervals not exceeding 4 1/2 ft and secured within 12 in. of boxes; 800.26 requires protection from physical damage.

800.110 requires communications cables to be listed and marked; plenum-rated cable (CMP) must be used in environmental air spaces per 300.22(C).

Article 820 CATV: 820.93 requires the outer conductive shield to be grounded; 820.100 requires a listed primary protector where the cable enters the building.

Article 830 network-powered broadband: 830.15 requires the system to be listed and the power source to be limited; 830.93 covers grounding of the shield.

Article 760 fire alarm: 760.130 requires separation of power-limited fire alarm circuits from power conductors; 760.154 covers support and securing of cables.

Article 770 optical fiber: 770.24 requires support at intervals not exceeding 4 1/2 ft; 770.48 covers the marking of fiber cables for the application.

250.52(A)(1) metal underground water pipe: must be in direct contact with the earth for 10 ft or more and must be supplemented by another electrode per 250.53(D)(2).

250.52(A)(4) ground ring: at least 20 ft of bare copper conductor, 2 AWG or larger, encircling the building and in direct contact with the earth at a depth of at least 2 1/2 ft.

250.52(A)(5) rod and pipe electrodes: must be at least 8 ft long and 5/8 in. diameter for rods; pipe electrodes must be at least 3/4 in. trade size.

250.53(A)(1) requires rod, pipe, and plate electrodes to be installed below permanent moisture level and, where practicable, below the frost line.

250.64 covers GEC installation: the GEC must be continuous, securely fastened, and protected from physical damage; 250.64(C) permits irreversible splices.

250.68 requires the grounding electrode conductor connection to be accessible and made with listed connectors; 250.70 lists the permitted connection methods.

250.102 bonding jumpers: sized per Table 250.102(C)(1) based on the largest ungrounded conductor; the supply-side bonding jumper is sized the same way.

250.190 covers grounding and bonding of equipment over 1000 V; the equipment grounding conductor must be sized per Table 250.122 and bonded to the enclosure.

Table 310.16 aluminum THHN at 30°C: 12 AWG = 25 A, 10 AWG = 35 A, 8 AWG = 45 A, 6 AWG = 55 A, 4 AWG = 75 A, 2 AWG = 100 A, 1/0 = 135 A, 250 kcmil = 230 A.

310.15(B)(3)(a) requires adjustment for conductors in raceways or cables where the number of current-carrying conductors exceeds three; the adjustment applies before ambient correction.

240.4(A) requires the overcurrent device to protect conductors against overcurrent; 240.4(B) next-size-up is limited to devices rated 800 A or less and does not apply to multioutlet branch circuits.

240.4(C) requires the overcurrent device rating not to exceed the ampacity of the conductors for circuits over 800 A, unless the conductor is listed for the higher temperature.

210.8 requires GFCI protection for 125 V, 15–20 A receptacles in dwelling unit bathrooms, kitchens, garages, outdoors, and other specified locations.

210.12 requires arc-fault circuit interrupter protection for 120 V, 15–20 A branch circuits in dwelling unit bedrooms, living rooms, and similar areas.

430.53 permits several motors on one branch circuit where the circuit is protected per 430.52 and the conductors are sized per 430.24; the overload devices must be sized per 430.32.

440.22 requires the branch-circuit short-circuit and ground-fault protection for air-conditioning equipment to be sized per the nameplate maximum overcurrent device rating.

314.16(A) box volume: a 4 × 4 × 1 1/4 in. box has 18 cu in.; a 4 × 4 × 2 1/8 in. box has 30.3 cu in.; a 4 11/16 × 4 11/16 × 2 1/8 in. box has 42 cu in.

314.16(B)(5) requires each conductor looped around a terminal to count once; 314.16(B)(6) counts equipment grounding conductors as one based on the largest size.

314.28(A)(1) straight pulls: the minimum distance from the raceway entry to the opposite wall is 8 times the trade size of the largest raceway.

314.30 handhole enclosures: must be listed and have a cover; the cover must be accessible and the enclosure must be sized per 314.28.

300.5(A) burial depth for direct-buried conductors: 24 in. for direct burial, 18 in. for residential branch circuits 120 V or less with GFCI, 6 in. under a concrete slab.

300.5(I) requires a warning ribbon or tape to be placed at least 12 in. above direct-buried conductors or raceways where the burial depth is less than 18 in.

300.22(B) ducts: only metal raceways or metal-clad cable may be installed in ducts used for dust, vapor, or air; 300.22(C) covers plenums.

314.23 requires boxes to be supported by structural members or other approved means; 314.23(C) permits boxes to be supported by raceways where the raceway is threaded into the box.

Article 500 Division 1: the hazard is present under normal operating conditions; Division 2: the hazard is present only under abnormal conditions.

Article 505 Zone 0 (continuous hazard), Zone 1 (normal operation), Zone 2 (abnormal operation) for gas atmospheres; Zone 20, 21, 22 for dust.

Article 511 commercial garages: 511.3 defines the classified area from the floor to 18 in. above the floor; 511.7 covers wiring in the classified area.

Article 517 patient care: 517.13(A) requires metal raceways or cables with a metal armor to provide a redundant ground path; 517.13(B) requires an insulated copper EGC.

Article 547 agricultural buildings: 547.10 requires equipotential planes at concrete slabs and metal equipment; 547.9 covers the service and grounding.

Article 680 pool: 680.26(B) requires bonding of metal parts within 5 ft of the pool; 680.23 covers underwater luminaires and requires GFCI protection.

Article 690 PV: 690.8 requires the PV source circuit current to be multiplied by 1.25 for continuous duty; 690.9 covers overcurrent protection.

Article 705 interconnection: 705.12 requires the sum of the overcurrent devices supplying a busbar to be at least 125% of the busbar rating for interactive systems.

Idaho electrical contractor license applicants must provide proof of experience and pass an examination administered or approved by the Idaho Electrical Board.

Idaho master electrician applicants must document a specified number of years of experience and pass the master examination; journeyman applicants must document supervised experience.

Idaho requires contractors to notify DOPL of any change in the designated master electrician or responsible licensee within the time set by board rule.

Idaho law requires electrical work to be performed in accordance with the adopted electrical code and the approved plans; deviations require approval from the AHJ.

Idaho requires inspections at specified stages: rough-in before covering, and final inspection after completion; the contractor must request inspections.

Idaho license numbers must appear on contracts, bids, and advertising for electrical contracting services; failure to display is a violation.

Idaho provides for reciprocity with some states for journeyman and master licenses; applicants must meet the board's reciprocity requirements.

Idaho law allows the board to investigate complaints, hold hearings, and impose discipline including fines, suspension, or revocation for code violations or unsafe work.

NFPA 70E 130.5 requires an arc flash risk assessment to determine the incident energy and the required PPE before work on energized equipment.

OSHA 1910.333(a)(1) requires de-energizing equipment before work unless the equipment is less than 50 V or de-energizing would introduce additional hazards.

Voltage-rated gloves must be tested every 6 months for Class 00–2 gloves; test intervals and storage requirements are set by ASTM D120 and the employer's program.

Insulated tools must be rated for the voltage and inspected before each use; damaged insulation or cracked handles require removal from service.

Temporary power: 590.4 requires receptacles to be of the grounding type and protected by GFCI; 590.5 requires the circuit to be protected by an overcurrent device.

Confined space: OSHA 1910.146 requires a permit, atmospheric testing, ventilation, and a rescue plan before entry; electrical work in wet or damp spaces requires extra precautions.

Battery safety: use insulated tools, remove jewelry, and provide eye protection when working on batteries; hydrogen gas from lead-acid batteries requires ventilation.

Emergency response: know the location of the disconnect, first aid kit, and AED; report all incidents and near misses to the supervisor.

Ohm's law for AC: V = I × Z, where Z is impedance; for resistive circuits Z = R and the power factor is 1.

Three-phase power: P = 1.732 × V × I × PF; apparent power S = 1.732 × V × I; reactive power Q = 1.732 × V × I × sin θ.

Conduit fill example: a 1 in. EMT has an allowable area of 0.346 sq in. at 40% fill; a 12 AWG THHN conductor has an area of 0.0133 sq in., so 25 conductors fit.

Voltage drop example: a 120 V, 20 A load 100 ft away on 12 AWG copper → VD = 2 × 12.9 × 20 × 100 / 6530 = 7.9 V, or 6.6%.

Ampacity example: 8 AWG THHN copper at 30°C = 55 A; in a 40°C ambient with 75°C insulation, 55 × 0.88 = 48.4 A; with 6 conductors, 48.4 × 0.80 = 38.7 A.

Motor calculation: a 10 HP, 230 V, three-phase motor has an FLC of 28 A per Table 430.250; branch-circuit conductors = 28 × 1.25 = 35 A.

Box fill example: a box with six 14 AWG conductors, two devices (four conductor equivalents), and one ground → 11 × 2.00 = 22 cu in. minimum.

Transformer example: a 45 kVA, 480–120/208 V three-phase transformer has a primary current of 45,000 / (1.732 × 480) = 54 A and a secondary current of 45,000 / (1.732 × 208) = 125 A.

Article 100: "approved" means acceptable to the authority having jurisdiction; "identified" means recognizable as suitable for the specific purpose, function, or environment.

Article 100: "enclosure" is a case or housing of apparatus that prevents accidental contact with live parts; "raceway" is a channel designed expressly for holding wires or cables.

90.3 states that Chapters 1–4 apply generally, Chapter 5 modifies or supplements, Chapter 6 covers special equipment, Chapter 7 covers special conditions, and Chapter 8 covers communications.

110.14(A) requires terminals to be identified for the conductor material; 110.14(C) limits conductor ampacity to the 60°C column for circuits 100 A or less unless the terminals are listed for higher temperatures.

110.26(A)(1) working space depth: 3 ft for 0–150 V to ground, 3 1/2 ft for 151–300 V, 4 ft for 301–600 V, and 5 ft for over 600 V, with additional depth for exposed live parts on both sides.

110.26(E) requires dedicated equipment space above and below switchboards and panelboards, typically 6 ft above and 30 in. wide.

Article 100: "grounded conductor" is a system or circuit conductor that is intentionally grounded; "grounding conductor" connects equipment to the grounding electrode.

110.21(A) requires marking of equipment with the manufacturer's name, trademark, or other descriptive marking, plus voltage, current, and other ratings.

Article 300.11 requires raceways and cables to be securely fastened in place and supported independently of ceiling grid systems unless listed for the purpose.

300.13 requires raceway and cable splices to be made only in boxes or conduit bodies; 300.14 requires at least 6 in. of free conductor at each outlet.

Article 310.10(G) permits conductors in parallel only where 1/0 AWG or larger, and requires the same length, conductor material, and insulation type.

Article 330 MC cable: 330.30 requires support at intervals not exceeding 6 ft and within 12 in. of boxes; 330.24 requires bends to be made without damaging the cable.

Article 338 SE cable: 338.10(B)(4) permits SE cable as a branch circuit or feeder where the bare conductor is used as the grounded conductor, and requires the bare conductor to be terminated at the neutral bar.

Article 340 UF cable: 340.10 permits direct burial and use in wet locations; 340.12 requires protection from physical damage where it emerges from the ground.

Article 352 PVC conduit: 352.44 requires expansion fittings where the conduit is exposed to temperature changes; 352.30 sets support spacing per trade size.

Article 358 EMT: 358.42 requires couplings and connectors to be listed for the conduit; 358.56 requires fittings to be made tight and to provide a ground path.

Article 725 Class 2 circuits are limited to 30 V and 100 VA; Class 3 circuits are limited to 150 V and 100 VA; the power source must be listed per 725.121.

725.139 requires Class 2 and Class 3 conductors to be installed in a Chapter 3 raceway or as permitted by 725.135; cables must be listed for the circuit class.

800.133(A)(1) requires at least 2 in. of separation between communications cables and power conductors, or a barrier, or a raceway.

800.100(A) requires a listed primary protector for communications circuits that are exposed to lightning or contact with power conductors; 800.100(B) covers the grounding conductor.

820.100 requires a listed primary protector for CATV cables; the protector must be grounded to the building grounding electrode system.

840.101 requires premises-powered broadband systems to be grounded and bonded to the building grounding electrode system.

760.130 requires power-limited fire alarm circuits to be separated from power conductors by at least 2 in., or by a barrier, or by a raceway.

770.48 requires optical fiber cables to be marked with the application and listed for the purpose; nonconductive fiber does not require grounding.

250.24(A)(1) requires the grounding electrode conductor to be connected to the grounded service conductor at the service equipment; 250.24(A)(2) permits the connection at the meter enclosure where listed.

250.24(C) requires the grounded conductor to be sized per Table 250.102(C)(1) and run with the service conductors to the service equipment.

250.30(A)(1) requires a system bonding jumper at the separately derived system; 250.30(A)(2) requires the grounding electrode conductor to be connected at the source.

250.32(B) requires an equipment grounding conductor to be run with the feeder to a separate building; the grounded conductor must not be used as the EGC.

250.94 requires an intersystem bonding termination for communications and other systems; it must be accessible and connected to the grounding electrode system.

250.104(A) requires metal water piping systems to be bonded to the service equipment enclosure or grounding electrode conductor; 250.104(B) covers other metal piping.

250.146 requires the grounding contact of receptacles to be connected to the equipment grounding conductor; 250.146(A) permits the yoke to serve as the ground path where the box is metal and the yoke is secured.

250.148 requires the equipment grounding conductor to be connected to the box and to the device where the box is nonmetallic.

Table 310.16 copper XHHW-2 at 30°C: 14 AWG = 25 A, 12 AWG = 30 A, 10 AWG = 40 A, 8 AWG = 55 A, 6 AWG = 75 A, 4 AWG = 95 A, 2 AWG = 130 A, 1/0 = 170 A, 250 kcmil = 290 A.

310.15(B)(2) requires ambient temperature correction for conductors in high-temperature locations; 310.15(B)(3) requires adjustment for conductor bundling.

240.4(D)(3) limits 10 AWG copper to 30 A; 240.4(D)(5) limits 14 AWG copper to 15 A; these limits apply to branch circuits and feeders unless specifically exempted.

240.21(B)(1) 10 ft tap rule: the tap conductor must have an ampacity of at least 1/10 of the overcurrent device rating and must terminate in a single circuit breaker or set of fuses.

240.21(B)(2) 25 ft tap rule: the tap conductor must have an ampacity of at least 1/3 of the overcurrent device rating and must be protected from physical damage.

430.52(C)(1) permits an inverse-time circuit breaker sized up to 250% of the motor full-load current; 430.52(C)(3) permits a dual-element fuse sized up to 175%.

440.22(A) requires the branch-circuit short-circuit and ground-fault protection for a single motor-compressor to be sized at 175% of the rated-load current, with a maximum of 225%.

210.20(A) requires the branch-circuit overcurrent device to be sized at 125% of the continuous load plus 100% of the noncontinuous load.

314.16(A) box volume for a 3 × 2 × 1 1/2 in. device box is 7.5 cu in.; a 3 × 2 × 2 in. box is 10 cu in.; a 3 × 2 × 2 1/4 in. box is 10.5 cu in.

314.16(B)(1) requires each conductor that originates outside the box and terminates inside to be counted once; conductors that pass through without splice count once.

314.28(A)(2) angle pulls: the minimum distance from the raceway entry to the opposite wall is 6 times the largest raceway trade size plus the sum of the other raceways on the same side.

314.28(A)(3) U pulls: the minimum distance between raceway entries is 6 times the largest raceway trade size, and the opposite wall must be at least 6 times the largest size plus the other raceways.

300.5(D)(2) requires direct-buried conductors to be protected by a raceway or guard where they emerge from the ground; the guard must extend at least 18 in. below grade.

300.22(C)(1) requires plenum-rated cable (CMP) or metal raceways in environmental air spaces; NM cable and PVC conduit are prohibited.

314.25 requires a cover or faceplate on every box; 314.27(A) requires boxes for luminaires to be listed and supported independently of the ceiling grid.

Article 376 wireways: 376.22 limits conductor fill to 20% of the wireway area; 376.30 requires supports at intervals not exceeding 5 ft.

Article 500 Class I Division 1: ignitable concentrations of flammable gases or vapors exist under normal conditions; Division 2: they exist only under abnormal conditions.

Article 501.15 requires sealing fittings at the boundary of Class I locations; 501.15(A)(1) requires a seal within 18 in. of the enclosure.

Article 502 Class II Division 1: combustible dust is present in quantities sufficient to produce explosive or ignitable mixtures; Division 2: dust is present only under abnormal conditions.

Article 503 Class III locations: easily ignitable fibers or flyings are present; 503.10 permits rigid metal conduit, IMC, and listed flexible connections.

Article 511 commercial garages: 511.3(A) defines the classified area from the floor to 18 in. above the floor; 511.7 requires wiring methods suitable for the classified area.

Article 517 patient care: 517.13 requires a redundant ground path; 517.19 requires isolated power for critical care areas; 517.30 covers essential electrical systems.

Article 547 agricultural buildings: 547.10 requires equipotential planes at concrete slabs and metal equipment; 547.9 requires a grounding electrode at the service.

Article 690 PV: 690.7 requires maximum PV system voltage to be calculated using the lowest expected ambient temperature; 690.8 requires 125% of the short-circuit current for conductor sizing.

Idaho Electrical Board rules require applicants for journeyman and master licenses to pass a written examination covering the NEC and Idaho law.

Idaho requires apprentices to be registered with DOPL and to work under the direct supervision of a licensed journeyman or master electrician.

Idaho electrical contractor licenses are issued to business entities; the contractor must designate a master electrician as the responsible licensee.

Idaho requires contractors to maintain general liability insurance and to provide a certificate of insurance to DOPL; the board may require a surety bond.

Idaho requires permits for electrical work; local building departments issue permits and conduct inspections under the adopted code.

Idaho license renewal requires continuing education hours set by DOPL rule; licensees must complete the required hours before the renewal date.

Idaho law prohibits unlicensed electrical contracting and provides for civil penalties, fines, and license revocation for violations.

Idaho adopts the NEC by reference with state amendments; the adopted edition and amendments are published by DOPL and local jurisdictions.

NFPA 70E 130.4 requires an shock risk assessment to determine the voltage and the limited, restricted, and arc flash approach boundaries.

OSHA 1910.335 requires employees to wear protective equipment for eyes, face, head, and extremities where exposed to electrical hazards.

Lockout/tagout: use a lock and tag on each energy-isolating device; verify the absence of voltage with a meter rated for the circuit.

GFCI protection is required for temporary receptacles on construction sites per 590.6; test GFCIs monthly and after any incident.

Ladder safety: maintain a 4:1 angle, secure the ladder, and keep at least 10 ft from energized overhead lines up to 50 kV.

Insulated gloves must be air-tested before each use and inspected for cuts, cracks, and ozone damage; remove damaged gloves from service.

Confined space entry requires a permit, atmospheric testing, ventilation, and a rescue plan; never enter alone.

Emergency response: de-energize the source before touching a shock victim, call 911, and begin CPR if trained.

Ohm's law: V = I × R; power: P = V × I; for three-phase, P = 1.732 × V × I × PF.

Voltage drop single-phase: VD = 2 × K × I × L / CM; three-phase: VD = 1.732 × K × I × L / CM; K = 12.9 for copper, 21.2 for aluminum.

Circular mils: CM = d² (d in mils); 1 mil = 0.001 in.; 1 kcmil = 1000 CM; 12 AWG = 6530 CM; 10 AWG = 10,380 CM; 8 AWG = 16,510 CM.

Box fill: 14 AWG = 2.00 cu in., 12 AWG = 2.25 cu in., 10 AWG = 2.50 cu in.; each device yoke counts as two conductors of the largest size.

Ampacity adjustment: Table 310.15(C)(1) reduces ampacity for more than three current-carrying conductors (80% for 4–6, 70% for 7–9, 50% for 10–20).

Motor calculation: FLC from Table 430.250; branch-circuit conductors = 125% of FLC; overload protection = 125% of nameplate FLA for a 1.15 service factor motor.

Transformer calculation: primary current = kVA × 1000 / (1.732 × primary voltage) for three-phase; secondary current = kVA × 1000 / (1.732 × secondary voltage).

Conduit fill: Chapter 9 Table 1 limits fill to 40% for three or more conductors; use Table 4 for the allowable area of each raceway type and size.