gh-ec-electrical-wiring-industrial key terms

A protective device that compares current leaving and returning on a circuit and opens the circuit when the imbalance exceeds a few milliamps, limiting electric shock risk to people.

The conductor that bonds non-current-carrying metal parts of equipment to the system grounding point, providing a low-impedance fault path so overcurrent devices clear faults quickly.

The conductor that connects the grounded circuit conductor or equipment grounding system to the grounding electrode, establishing a reference to earth potential.

A conductor sized to ensure electrical continuity between metal parts, used to connect raceways, enclosures, or electrodes so they remain at the same potential.

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

A graph showing how long a protective device takes to open at various current levels, used to coordinate devices so only the nearest one trips during a fault.

The intentional arrangement of overcurrent devices so that the device closest to a fault opens first, leaving upstream devices closed and minimizing outage scope.

A combination of a main breaker and downstream breakers tested together so the downstream device may have a lower interrupting rating than the available fault current, relying on the main to assist.

The maximum short-circuit current a device is rated to safely clear at a stated voltage, expressed in kiloamps, without failing or endangering personnel.

The maximum short-circuit current a system can deliver at a given point, determined by utility capacity, transformer impedance, and conductor impedance, used to select adequately rated equipment.

The voltage drop across a transformer winding at rated current, expressed as a percentage of rated voltage; it limits short-circuit current and affects voltage regulation.

The reduction in voltage along a circuit caused by conductor resistance and reactance carrying current; excessive drop causes poor equipment performance and motor overheating.

The maximum continuous current a conductor can carry under stated conditions without exceeding its temperature rating, adjusted for ambient temperature and number of current-carrying conductors.

Derating multipliers applied to a conductor's tabulated ampacity when ambient temperature differs from the table basis or when multiple current-carrying conductors share a raceway.

The percentage of a raceway's cross-sectional area occupied by conductors, limited by code to keep conductors from jamming and to allow heat dissipation.

A fitting installed in a conduit run that provides access for pulling conductors and making splices or bends, with volume limits on contained conductors.

The method of counting conductors, devices, fittings, and grounding conductors by volume allowances to confirm an enclosure is large enough for its contents.

The rules that set minimum dimensions for junction and pull boxes based on conduit trade size and whether the run is straight or angled, ensuring conductors can be pulled without damage.

A load expected to operate at maximum current for three hours or more, requiring conductors and overcurrent devices to be sized at 125 percent of the load.

The ratio of the maximum demand of a system to the total connected load, allowing feeders and services to be sized smaller than the sum of all loads.

A structured method of summing general lighting, receptacle, appliance, and motor loads with applicable demand factors to determine feeder and service capacity.

The overcurrent device protecting a motor branch circuit against short circuits and grounds, sized from motor full-load current using code tables rather than conductor ampacity.

A device that senses sustained excess current in a motor and opens the circuit to prevent winding damage from overheating, separate from short-circuit protection.

The current a motor draws at rated load and voltage, taken from code tables or the nameplate, used to size branch-circuit conductors and protective devices.

A device or assembly that starts and stops a motor and may provide overload protection, speed control, or reversing functions, rated for the motor's voltage and horsepower.

A motor controller that connects the motor directly to the supply at full voltage through contactors, providing simple start-stop control and overload protection.

An electronic controller that varies motor speed by changing supply frequency and voltage, often used for energy savings and process control, with special cable and grounding requirements.

Voltages or currents at integer multiples of the fundamental frequency, produced by nonlinear loads such as drives and rectifiers, causing conductor heating and neutral overload.

The ratio of real power in watts to apparent power in volt-amperes, indicating how much current is doing useful work versus circulating as reactive current.

An area where flammable gases, vapors, dusts, or fibers may be present in quantities sufficient to ignite, requiring special equipment and wiring methods.

The traditional classification scheme that groups hazardous materials by class and rates the likelihood of their presence by division, guiding equipment selection and installation rules.

An international scheme that classifies gas and dust hazards by zone numbers reflecting how often or how long an ignitable atmosphere is expected to exist.

A protection method that limits electrical energy in a circuit to levels too low to ignite a hazardous atmosphere, using barriers or isolators and special wiring rules.

An enclosure designed to contain an internal explosion and prevent ignition of surrounding flammable atmosphere, with flame paths that cool escaping gases.

A device that detects the current and voltage signature of arcing and opens the circuit to reduce the chance of fire from damaged wiring or connections.

The clear area required in front of electrical equipment, with depth based on voltage and condition, so workers can safely operate and service energized parts.

The distance from energized equipment within which a person could receive a second-degree burn from an arcing fault, used to select protective clothing.

A procedure that isolates energy sources with locks and tags before work, preventing accidental energization or release of stored energy during maintenance.

Acceptable to the authority having jurisdiction, typically because a product is listed by a recognized testing laboratory or meets an established safety standard.