Electrical Glossary

The maximum amount of electrical current a conductor can carry continuously without exceeding its temperature rating. Ampacity depends on conductor size, insulation type, installation method, ambient temperature, and number of conductors in a raceway.

A standardized wire gauge system used in North America for measuring the diameter of electrically conducting wire. Lower AWG numbers indicate larger wire diameters. For example, 10 AWG is larger than 14 AWG. Each decrease of 3 gauge numbers doubles the cross-sectional area.

The circuit conductors between the final overcurrent protection device and the outlet(s). Branch circuits supply current to lighting, receptacles, and equipment. NEC recommends maximum 3% voltage drop for branch circuits.

A unit of area equal to the area of a circle with a diameter of one mil (0.001 inch). Used to express wire cross-sectional area. One circular mil = π/4 square mils ≈ 0.7854 square mils.

A material that allows electrical current to flow through it with relatively low resistance. Common electrical conductors include copper and aluminum. Conductor size directly affects voltage drop - larger conductors have lower resistance.

A tube or trough used to protect and route electrical wiring. Types include EMT (Electrical Metallic Tubing), IMC (Intermediate Metal Conduit), RMC (Rigid Metal Conduit), and PVC (Polyvinyl Chloride). Steel conduit can increase impedance in AC systems due to magnetic effects.

The rate of flow of electric charge, measured in amperes (A). Current is one of the primary factors in voltage drop calculations. Higher current results in greater voltage drop for a given conductor size and length.

The process of reducing the ampacity of a conductor due to factors such as ambient temperature above 30°C, number of current-carrying conductors in a raceway, or continuous loading. Derating ensures conductors operate within safe temperature limits.

A thin-walled metal conduit used to protect electrical wiring. EMT is lighter and easier to bend than rigid conduit. It is commonly used in commercial and industrial installations but not permitted in some hazardous locations.

All circuit conductors between the service equipment (or source of separately derived system) and the final branch-circuit overcurrent device. Feeders supply branch circuit panels or large equipment. Total voltage drop (feeder + branch) should not exceed 5%.

An unintentional electrical path between a current-carrying conductor and a grounded surface. Ground faults can cause equipment damage, fires, and electrical shock. GFCI protection is required in certain locations per NEC.

The total opposition to current flow in an AC circuit, combining resistance (R) and reactance (X). Impedance is measured in ohms. For voltage drop calculations, impedance is more accurate than resistance alone for AC systems, especially with large conductors in steel conduit.

A unit of measurement for conductor cross-sectional area, where 1 kcmil = 1,000 circular mils. Used for large conductors (typically 250 kcmil and above). Formerly abbreviated MCM (thousand circular mils).

Any device or equipment that consumes electrical power. Load can be measured in amps, watts, VA, or horsepower. Accurate load calculation is essential for proper wire sizing and voltage drop analysis.

A set of standards for safe electrical installation in the United States, published by NFPA. NEC provides guidelines for voltage drop limits: 3% for branch circuits and 5% total (feeder + branch). Updated every three years.

The fundamental relationship between voltage (V), current (I), and resistance (R): V = I × R. This law is the basis for all voltage drop calculations. Voltage drop equals current times resistance of the conductor.

Devices (circuit breakers or fuses) that automatically interrupt current flow when it exceeds a safe level. Overcurrent protection prevents conductor overheating and fire hazards. Sized based on conductor ampacity per NEC.

Two or more conductors of the same size, material, and length connected together to increase current-carrying capacity and reduce voltage drop. Per NEC, parallel conductors must be 1/0 AWG or larger and installed with specific arrangements.

The ratio of real power (watts) to apparent power (VA) in an AC circuit. Power factor ranges from 0 to 1. A power factor of 1.0 indicates a purely resistive load. Inductive loads (motors, transformers) have lagging power factor, which affects voltage drop calculations.

Opposition to AC current flow caused by inductance or capacitance, measured in ohms. Inductive reactance (XL) increases with frequency; capacitive reactance (XC) decreases with frequency. Reactance contributes to total impedance in AC circuits.

Opposition to current flow in a conductor, measured in ohms (Ω). Resistance depends on conductor material, cross-sectional area, length, and temperature. Copper has lower resistance than aluminum for the same size.

The conductors and equipment for delivering electrical energy from the utility supply to the premises wiring. Service includes the service drop (overhead) or service lateral (underground), meter, and main disconnect.

An AC power system with one phase conductor and a neutral. Common in residential (120V and 240V) and light commercial applications. Voltage drop formula uses factor of 2 for single-phase circuits: Vd = 2 × I × L × R / 1000.

The maximum temperature at which a conductor's insulation can operate continuously without degradation. Common ratings: 60°C, 75°C, and 90°C. Higher temperature ratings allow greater ampacity but don't change the conductor's resistance for voltage drop calculations.

An AC power system with three phase conductors, 120° apart. More efficient for large loads and motors. Voltage drop formula uses factor of √3 (1.732): Vd = √3 × I × L × R / 1000. Common voltages: 208V, 480V.

The reduction in voltage between the source and load due to conductor resistance. Expressed in volts or as a percentage of source voltage. NEC recommends 3% max for branch circuits and 5% total. Excessive drop causes equipment issues and energy waste.

The unit of electrical power equal to one joule per second. In DC or purely resistive AC circuits: P = V × I. For AC circuits with power factor: P = V × I × PF. Used to calculate current draw for voltage drop analysis.