Licensed Electrical Inspector (LEI) G Class Theory key terms

The fixed relationship stating that voltage equals current multiplied by resistance, and that current equals voltage divided by resistance. It lets an inspector predict one circuit quantity when the other two are known.

A circuit in which components form a single path, so the same current flows through every element while the source voltage divides among them. Total resistance is the sum of individual resistances.

A circuit in which components connect across the same two points, so voltage is common to all branches while current divides among them. Total resistance is always lower than the smallest branch resistance.

The reduction in voltage along conductors caused by their impedance as current flows. Excessive drop starves equipment of voltage and wastes energy, so conductors are often upsized to limit it.

The ratio of real power doing useful work to apparent power supplied to an alternating-current load. A low value means more current is drawn for the same useful output.

The maximum continuous current a conductor can carry under stated conditions without exceeding its temperature rating. It depends on material, size, insulation, ambient temperature, and how many conductors share a raceway.

Adjustment of a conductor's tabulated current rating to account for real installation conditions such as high ambient temperature or several current-carrying conductors bundled together. The corrected value governs whether the conductor is adequately protected.

A multiplier below one applied to a tabulated ampacity because of grouping, ambient heat, or other adverse conditions. Applying it produces the usable current rating for the actual installation.

A breaker or fuse that automatically opens a circuit when current exceeds its rating, protecting conductors and equipment from overheating. Its rating must coordinate with conductor ampacity and the load served.

A system that detects current leaking from an intended path to ground and quickly disconnects the circuit. It protects people from shock and equipment from arcing damage, and is required in many wet or high-risk locations.

The conductor that connects the metal frames of equipment to the grounding system, giving fault current a low-impedance return path. It carries current only during a fault, not under normal operation.

A conductor that intentionally connects metal parts so they remain at the same electrical potential. It prevents dangerous voltage differences between enclosures, piping, and grounded surfaces during faults.

A conductive object, such as a rod or metal water pipe, that establishes a direct connection to the earth. It anchors the electrical system to earth potential and helps dissipate fault and surge energy.

An unintended low-resistance path that lets current bypass the normal load, producing very high current. It triggers protective devices and can damage conductors or start fires if protection is inadequate.

A fault in which current crosses an air gap between damaged or loose conductors, generating intense heat and sparks. It often draws too little current to trip a standard breaker, so special detection is used.

An enclosed channel such as conduit or tubing designed to hold and protect conductors. Its fill, support, and bend requirements limit heat buildup and mechanical stress on the wires inside.

The proportion of a raceway's cross-sectional area occupied by conductors. Keeping fill within limits preserves space for heat dissipation and makes pulling wires without insulation damage feasible.

The calculated volume of an outlet or junction box compared with the space required by the conductors, devices, and fittings it contains. Adequate volume prevents overcrowding and insulation damage.

A rigid open support system used to carry cables or raceways across a structure. Its design allows inspection of cable routing and provides mechanical support while permitting heat to escape.

The clear area in front of electrical equipment that must remain unobstructed so workers can safely operate, inspect, and service it. Its depth and width depend on voltage and equipment conditions.

The zone above and around electrical equipment reserved exclusively for that equipment, free of piping, ducts, and unrelated wiring. It keeps foreign systems from blocking access or damaging the installation.

An official authorization issued before regulated electrical work begins, confirming that plans meet applicable requirements. Inspections are typically scheduled against the permit, which must remain posted or available on site.

The pre-construction examination of drawings and specifications to verify compliance with code, load calculations, and local rules. It catches design errors before costly installation occurs.

A drawing updated to show the installation as actually constructed, including field changes from the approved design. Inspectors use it to confirm that deviations were reviewed and accepted.

The inspection performed after wiring, boxes, and raceways are installed but before walls or ceilings are closed. It verifies concealed work while it is still visible and correctable.

The last inspection, conducted when work is complete, to confirm devices, labeling, grounding, and clearances are correct. Passing it normally allows the authority to approve the installation for use.

A written record listing deficiencies found during inspection and the code basis for each. It requires the contractor to correct the items and request reinspection before approval is granted.

An official document confirming that a building or altered space complies with applicable regulations and may be legally used. Electrical approvals are usually a prerequisite before it is issued.

A safety procedure that isolates energy sources and applies locks and warning tags so equipment cannot be re-energized while someone works on it. It is a core safeguard during inspection and repair.

Specialized clothing and gear, such as insulated gloves, arc-rated clothing, and eye protection, worn to reduce injury from electrical, thermal, and mechanical hazards. Selection depends on the task risk assessment.

A sudden release of intense heat, light, and pressure caused by an electrical arc through air. It can severely burn or kill workers, so arc-rated protection and safe work distances are required near energized equipment.

Electrical work performed on or near conductors that remain electrically live. It is permitted only under strict conditions with justified need, hazard analysis, and appropriate protective equipment.

An area where flammable gases, vapors, dusts, or fibers may be present in quantities that could ignite. Equipment and wiring methods there must be specially rated and installed to prevent ignition.

A housing designed to contain an internal explosion and prevent flame from igniting surrounding atmosphere. It also keeps the enclosure cool enough that external surfaces cannot ignite nearby flammable material.

A circuit designed so that its electrical energy is too low, even under fault conditions, to ignite a flammable atmosphere. It relies on limiting voltage and current rather than heavy enclosures.

A situation in which an inspector's personal, financial, or professional interests could improperly influence inspection judgments. It must be disclosed and avoided so findings remain impartial and credible.

The degree of skill and diligence that a reasonably competent inspector would exercise under similar circumstances. Falling below it can support a claim of negligence or professional liability.

Failure to exercise the care a reasonable professional would provide, resulting in harm or loss. For inspectors, it typically involves missed defects, inadequate documentation, or exceeding the agreed scope of work.

The written description of what an inspection will and will not cover, including systems examined and limitations. Clear scope language helps manage client expectations and limits liability for excluded items.