NASCLA Journeyman Electrician key terms

The maximum current, in amperes, that a conductor can carry continuously under stated conditions of use without exceeding its temperature rating and damaging its insulation.

The temperature of the air or surroundings where conductors or equipment are installed. Higher ambient temperatures reduce how much current a conductor can safely carry and require ampacity adjustment.

The loss of voltage along a conductor caused by its resistance and reactance as current flows. Excessive drop at the load causes poor equipment performance and is limited by code for feeders and branch circuits.

The relationship stating that voltage equals current multiplied by resistance, written E = I x R. Electricians use it to find an unknown current, voltage, or resistance in a circuit.

The ratio of real power in watts to apparent power in volt-amperes in an alternating-current circuit. It is 1.0 for pure resistance and lower when motors or other inductive loads are present.

A load that operates at its maximum current for three hours or longer, such as store lighting. Conductors and overcurrent devices serving it must generally be sized at 125 percent of the load.

The ratio of the maximum demand on a system to the total connected load it supplies. It allows panelboards, feeders, and services to be sized smaller than the sum of every load running at once.

All circuit conductors between the service equipment, or a separately derived source, and the final branch-circuit overcurrent device. Feeders supply panelboards rather than individual outlets.

The circuit conductors between the final overcurrent device protecting the circuit and the outlets or utilization equipment it supplies. It is the last level of wiring in the distribution system.

The conductors that connect the utility supply, usually at the service point, to the service equipment of the building. They carry the entire connected load of the premises.

A fuse or circuit breaker that opens the circuit automatically when current exceeds a safe level, protecting conductors and equipment from overheating and damage.

A device that compares current leaving and returning on a circuit and trips when a small imbalance shows current leaking to ground, protecting people from shock, especially in wet areas.

A device that detects the signature of dangerous arcing in branch-circuit wiring and de-energizes the circuit, reducing the chance of fire from damaged or loose conductors.

The circuit conductor intentionally connected to earth at the source, commonly called the neutral. It carries return current in normal operation and is finished white or gray.

The conductor that connects the non-current-carrying metal parts of equipment and enclosures to the grounding electrode system, giving fault current a low-impedance path so overcurrent devices open.

A conductor that ensures electrical continuity between metal parts that must be electrically connected, so they stay at the same potential and can safely carry fault current.

Reducing a conductor's allowable current because of conditions such as high ambient temperature or more than three current-carrying conductors installed together in a raceway, cable, or bundle.

The required internal volume of an outlet or junction box, calculated from the number and size of conductors, devices, fittings, and grounds it contains, so wiring is not crowded or damaged.

The percentage of a raceway's cross-sectional area that conductors may occupy, limited by code so wires can be pulled without damage and heat can dissipate.

An enclosed channel of metal or nonmetallic tubing, such as conduit, designed to hold and protect wires and cables and to allow them to be pulled in or out.

An enclosure where conductors from several raceways or cables are joined, spliced, or tapped. It must remain accessible and be sized to hold all conductors and splices safely.

A contact device installed at an outlet for the connection of a plug and flexible cord. It supplies portable and stationary equipment with power.

The clear, unobstructed space required in front of electrical equipment such as panelboards and switchgear so people can safely work on it while it is energized.

The current a motor draws when running at rated horsepower, speed, and voltage with a rated load. Code tables list typical values used to size branch-circuit conductors and protection.

A device, such as a thermal overload relay, that protects the motor from sustained excess current that would overheat the windings. It does not clear short circuits or grounds.

The fuse or circuit breaker ahead of a motor that clears short circuits and grounds, sized from the motor's full-load current with allowances for starting inrush. It does not protect against overload.

A multiplier stamped on a motor nameplate showing how far above rated horsepower the motor may run without overheating. It affects how much overload protection the motor is permitted to have.

A device with two or more windings that transfers electrical energy by electromagnetic induction, changing voltage and current levels while leaving the frequency unchanged.

The number of turns in the primary winding divided by the number in the secondary. It equals the primary-to-secondary voltage ratio and the inverse of the current ratio.

The apparent-power capacity of a transformer or generator, in thousands of volt-amperes, that it can deliver without exceeding its rated temperature rise. It equals voltage times current.

An area where fire or explosion hazards may exist because of flammable gases, vapors, dusts, or fibers. Wiring there is restricted to methods approved for the specific class and division or zone.

A circuit designed so that any spark or thermal effect produced in normal or fault conditions cannot ignite a flammable atmosphere, typically by limiting voltage and current energy.

A procedure in which an energy-isolating device is locked and tagged by each worker so equipment cannot be re-energized until all work is finished and every lock is removed.

Clothing and gear such as insulated gloves, arc-rated clothing, hard hats, and eye protection worn to reduce injury from electrical, thermal, and physical hazards on the job.

A sudden release of heat, light, and pressure caused by an electric arc between energized conductors or from a conductor to ground, capable of causing severe burns.

A shock-protection distance from exposed energized parts that unqualified persons may not cross unless escorted and protected. It is one of the approach boundaries defined for electrical work.

A method of adding up connected loads, applying demand factors, and applying code allowances to determine the size of the service, feeders, and panelboards required.

A drawing that shows the electrical distribution system with single lines for circuits and symbols for equipment, so feeders, breakers, and transformers can be traced from source to load.