Licensed Electrical Inspector (LEI) G Class Theory cheat sheet

Ohm's law: E = I × R; power P = E × I = I²R = E²/R. In AC circuits substitute impedance Z for R and use RMS values.

Series circuit: current is identical everywhere; resistances add (R_T = R₁+R₂+…); voltage divides in proportion to resistance.

Parallel circuit: voltage is identical across branches; conductances add (1/R_T = 1/R₁+1/R₂+…); branch currents divide inversely with resistance.

Single-phase power: P = E × I × PF for unity and non-unity loads; apparent power S in VA = E × I; reactive power Q in VAR = E × I × sin θ.

Balanced three-phase: P = √3 × E_line × I_line × PF; line voltage = √3 × phase voltage in wye; line current = √3 × phase current in delta.

Conductor resistance R = ρL/A, where ρ is resistivity (circular-mil-ohm per foot for copper ≈ 12.9 at 75 °C); resistance rises with temperature.

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

Transformer turns ratio: E_primary/E_secondary = N_primary/N_secondary; power is essentially constant, so current ratio is inverse of voltage ratio.

Impedance Z = √(R² + X²); inductive reactance X_L = 2πfL; capacitive reactance X_C = 1/(2πfC); resonance occurs when X_L = X_C.

Conductor ampacity depends on insulation temperature rating, ambient temperature correction, and adjustment for more than three current-carrying conductors in a raceway.

NM-B cable is permitted in dry interior locations but not in wet locations, exposed to weather, embedded in masonry, or in hazardous locations.

Rigid metal conduit, IMC, and EMT differ in wall thickness and permitted uses; EMT is not permitted where severe physical damage is likely unless protected.

Box fill is calculated by counting each conductor, each device yoke, each clamp, and each equipment grounding conductor by assigned volume, then comparing with the box's marked cubic-inch capacity.

Support intervals are method-specific: EMT within 3 ft of boxes and at intervals not exceeding 10 ft; rigid metal conduit at intervals not exceeding 10 ft.

Bending radius and number of bends between boxes are limited to protect conductor insulation; no more than 360° of bends is permitted between pull points.

Cable and raceway entries into boxes require approved connectors, and unused openings must be closed with listed plugs or covers.

Conductor identification is color- and marking-based: grounded conductor white or gray, equipment grounding conductor green or bare, ungrounded conductors other colors.

Wet-location and underground installations require conductors and raceways listed for wet locations; direct-burial cable must be listed and buried at the required depth.

The equipment grounding conductor provides a low-impedance fault path so overcurrent devices open quickly; it is not a current-carrying circuit conductor under normal operation.

The grounded (neutral) conductor is bonded to the enclosure and grounding electrode system at the service only; downstream panels keep neutral and ground separated.

Overcurrent device ratings must not exceed conductor ampacity after correction and adjustment, and the next standard size rule allows limited rounding up for certain loads.

Fuses and circuit breakers protect against overload and short circuit; ground-fault circuit interrupters protect people from line-to-ground leakage, and arc-fault devices detect arcing.

Grounding electrode systems may include metal water pipe, concrete-encased electrode, ground ring, and rod electrodes; the electrode conductor sizing follows the code table.

Bonding jumpers are required around water meters, gas piping, and other components that could interrupt the grounding path.

Selective coordination arranges overcurrent devices so the device nearest a fault opens first, preserving upstream service.

Series-rated systems require the downstream device to be listed for use with the specific upstream device; untested combinations are not permitted.

Available fault current at the service must be compared with the interrupting rating of every overcurrent device in the system.

A permit is generally required before installing or altering electrical wiring; ordinary minor repair and replacement work is often exempt but must still comply with code.

Plan review precedes permit issuance for larger projects; approved plans must be kept on site and work must match the approved drawings.

Inspections are typically staged: rough-in before concealment, and final after devices, fixtures, and labeling are complete.

The adopting jurisdiction's code edition governs; the model code applies only as amended and adopted locally.

Licensing rules define who may perform electrical work and who may supervise apprentices; unlicensed contracting is a violation.

Stop-work orders may be issued when work proceeds without a permit or in an unsafe manner; work must cease until the issue is resolved.

Certificate of occupancy or final approval is issued only after all required inspections pass and any corrections are verified.

Records of inspections, corrections, and re-inspections must be retained per the jurisdiction's retention schedule.

Utility connection approval typically requires an inspection release or cut-in card from the authority having jurisdiction.

Plan review checks load calculations, service size, conductor and overcurrent ratings, grounding design, and compliance with adopted code editions.

A systematic inspection sequence covers service equipment, feeders, panelboards, branch circuits, boxes, devices, and fixtures in that order.

Test instruments include low-resistance ohmmeters for continuity, insulation resistance testers, clamp meters, and receptacle testers with GFCI/AFCI functions.

Documentation should record date, location, code references for deficiencies, corrective actions requested, and re-inspection results.

Photographs and marked-up drawings support findings and provide evidence if a decision is later disputed.

Deficiency notices should cite the specific code section and describe the observed condition, not merely state that work is noncompliant.

Final inspection verifies labeling of circuits and disconnects, directory accuracy, cover plates, and accessibility of equipment.

Inspection reports should distinguish code violations from recommendations to avoid implying authority beyond the code.

Energized work requires a permit, a risk assessment, appropriate PPE, and qualified persons; de-energization is the default control.

Lockout/tagout isolates energy sources, verifies absence of voltage with a tested meter, and prevents unexpected re-energization.

Arc flash risk depends on available fault current, clearing time, and working distance; boundaries define required PPE levels.

Approach boundaries include limited, restricted, and prohibited distances; unqualified persons must stay outside the limited approach boundary.

PPE categories include arc-rated clothing, face shields, insulating gloves with leather protectors, and insulated tools rated for the voltage.

Hazard identification considers shock, arc flash, fire, fall, confined space, and environmental hazards such as wet locations.

Risk assessment ranks hazards by severity and likelihood, then applies controls in order: elimination, substitution, engineering, administrative, and PPE.

Test-before-touch is mandatory; meters and test leads must be rated for the voltage and category of the circuit being tested.

Incident investigation documents root cause and corrective action to prevent recurrence and support regulatory reporting.

Hazardous locations are classified by class, division or zone, and group; equipment must be listed for the specific classification.

Class I locations involve flammable gases or vapors; Class II involves combustible dust; Class III involves ignitable fibers.

Health care facilities require redundant grounding, isolated power in critical care areas, and special receptacle requirements.

Assembly occupancies impose stricter requirements for emergency lighting, exit signage, and wiring methods in egress paths.

Fire pumps require dedicated, reliable supply conductors routed to survive fire conditions and protected from overload.

Emergency and legally required standby systems must be separate from normal power and tested periodically.

Photovoltaic systems require rapid shutdown provisions, listed DC-rated equipment, and labeling of disconnects and conductors.

Electric vehicle supply equipment requires GFCI protection, listed connectors, and load management where the service capacity is limited.

Swimming pools, spas, and fountains require equipotential bonding, GFCI protection, and restrictions on overhead conductors.

Inspectors must act within their authority, applying only adopted code provisions and not personal preference.

Conflicts of interest, including financial interest in inspected work, must be disclosed and avoided.

Inspectors should not accept gifts or favors that could influence enforcement decisions.

Findings must be documented objectively and consistently; identical conditions should receive identical treatment.

Confidentiality applies to plans, proprietary designs, and business information obtained during inspection.

Negligent inspection can create liability for the jurisdiction and the inspector; accurate records are the primary defense.

Inspectors must maintain competence through continuing education and stay current with code editions and amendments.

Communication with contractors and owners should be professional, respectful, and focused on code compliance.

Inspectors must not perform design or installation work on projects they inspect, to preserve independence.