ND Electrician key terms

The fixed relationship in a DC circuit where voltage equals current multiplied by resistance (E = I × R). Knowing any two values lets you calculate the third for troubleshooting and sizing conductors.

The electrical potential difference between two points, measured in volts, that pushes charge through a circuit. Often called electromotive force and supplied by utility service, batteries, or generators.

The rate of electron flow through a conductor, measured in amperes. Current is what produces heating in conductors and determines the ampere rating of overcurrent devices and conductor ampacity.

Opposition to current flow in a circuit, measured in ohms. It converts electrical energy to heat and depends on conductor material, length, cross-sectional area, and temperature.

The rate of electrical energy use, measured in watts. In a resistive circuit it equals voltage times current (P = E × I), and it underlies load calculations for services and feeders.

The ratio of true power in watts to apparent power in volt-amperes in an AC circuit, ranging from 0 to 1. Low power factor means larger current for the same useful work.

The product of RMS voltage and RMS current in an AC circuit, expressed in volt-amperes. It includes both true power and reactive power and sizes transformers and generators.

The total opposition to alternating current, measured in ohms, combining resistance with inductive and capacitive reactance. It determines current magnitude and phase angle in AC circuits.

The opposition to alternating current caused by inductance or capacitance, measured in ohms, that stores and returns energy rather than dissipating it as heat. It varies with frequency.

The property of a coil or conductor that opposes any change in current by producing a counter voltage, measured in henries. It causes current to lag voltage in AC circuits.

The ability to store electric charge between two conductors separated by an insulator, measured in farads. In AC circuits it causes current to lead voltage and can correct lagging power factor.

Current that reverses direction periodically, typically 60 hertz in North American power systems. AC is the standard supply because it is easily transformed between voltage levels for distribution.

Current that flows in one direction only, supplied by batteries, rectifiers, and photovoltaic modules. DC circuits follow Ohm's law directly and have no frequency-related reactance.

The number of complete AC cycles per second, measured in hertz. North American power systems operate at 60 hertz, which affects transformer sizing, motor speed, and reactance values.

The effective value of an alternating quantity, equal to the DC value that would produce the same heating. For a sine wave it is about 0.707 times the peak value.

The reduction in voltage along a conductor caused by impedance and current, expressed in volts or percent. Excessive drop causes dim lights and poor motor performance and is limited by code recommendations.

A circuit path where components connect end to end so the same current flows through all of them and the total resistance is the sum of individual resistances. A break stops all current.

A circuit where components connect across the same two points, so each receives the full source voltage and total current is the sum of branch currents. This is typical of building wiring.

A deliberate connection between an electrical system or equipment and the earth or a grounded conductor, providing a reference and a low-impedance fault path that helps clear faults safely.

The permanent joining of metal parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct any likely fault current safely.

The conductor that connects non-current-carrying metal parts of equipment to the system grounding point, providing a fault current path so overcurrent devices operate during a ground fault.

The circuit conductor intentionally connected to ground, usually the white or gray neutral. It carries normal return current and must be kept separate from grounding conductors except at service equipment.

The maximum current a conductor can carry continuously under stated conditions without exceeding its temperature rating. It depends on conductor size, insulation type, and ambient temperature.

A device such as a fuse or circuit breaker that opens a circuit automatically when current exceeds a set value for a set time, protecting conductors and equipment from overheating and damage.

A resettable automatic switch that opens a circuit on overload or short circuit. Its rating and trip curve must coordinate with conductor ampacity and the load being served.

A one-time overcurrent device containing a metal element that melts when current exceeds its rating, opening the circuit. Fuses must be replaced with the same type and rating.

The equipment at the supply end of a premises wiring system, including service conductors, main disconnect, and metering, that lets the building's power be disconnected and protected.

A single panel containing busbars and overcurrent devices that distributes power to branch circuits or feeders. It is typically installed in a cabinet accessible only to qualified persons.

The circuit conductors between the final overcurrent device protecting the circuit and the outlets or equipment it supplies. Branch circuits feed lighting, receptacles, and individual appliances.

The circuit conductors between the service equipment or source and the final branch-circuit overcurrent device. Feeders are sized for the total calculated load they carry.

Selecting a conductor's cross-sectional area and insulation rating so its ampacity meets or exceeds the calculated load and is protected by the chosen overcurrent device.

A load expected to operate at maximum current for three hours or more. Code requires such loads to be calculated at 125 percent of their rating when sizing conductors and overcurrent devices.

The method of totaling connected loads, applying demand factors, and adding required allowances to determine the minimum service, feeder, and branch-circuit capacity for a building.

The ratio of the maximum demand on a system to the total connected load, used to account for loads that do not operate simultaneously and to avoid oversizing services and feeders.

A device that opens a circuit when it detects a small current imbalance between hot and neutral, protecting people from shock in wet or damp locations such as bathrooms and outdoors.

A device that detects the signature of dangerous arcing in wiring and opens the circuit, reducing the risk of fire from damaged conductors or loose connections in dwelling branch circuits.

A unit of electrical energy equal to 1,000 watts used for one hour. Utility billing is based on this measure, which combines power demand with time of use.