NICET EPT key terms

The distance from energized equipment at which an arc flash could cause second-degree burns to unprotected skin; it sets where barricades go and what protective clothing is required.

The thermal energy per unit area deposited on a surface during an arc flash, usually stated in calories per square centimeter; it determines the arc rating of clothing workers must wear.

A shock-protection boundary around exposed energized parts that unqualified people may not cross; only qualified workers using proper protective equipment and a plan may enter.

A formal procedure for isolating energy sources, attaching locks and tags, and confirming zero energy before work starts, preventing unexpected energization or release of stored energy.

The arc thermal performance value of protective clothing: the incident energy at which there is a 50 percent chance of second-degree burn through the fabric.

The relationship stating that voltage equals current times resistance in a resistive circuit, so any one of the three quantities can be calculated when the other two are known.

The principle that total current entering a junction equals total current leaving it, since charge cannot pile up at a node; it is the basis for nodal circuit analysis.

The principle that the algebraic sum of all voltage rises and drops around any closed loop is zero, reflecting conservation of energy in a circuit.

The ratio of real power in watts to apparent power in volt-amperes in an AC circuit, equal to the cosine of the angle between voltage and current.

A method that resolves an unbalanced three-phase set of voltages or currents into three balanced sets called positive, negative, and zero sequence, used for fault and relay studies.

The ratio of primary winding turns to secondary winding turns, which determines the ratio of primary to secondary voltage and the inverse ratio of currents.

The percentage of rated voltage that must be applied to one winding to circulate rated current through the other winding short-circuited; it limits available short-circuit current.

The instantaneous voltage direction relationship between primary and secondary windings, marked additive or subtractive, which must be known to parallel transformers or build three-phase banks.

A code such as Dyn11 that describes a three-phase transformer's winding connections and the phase angle displacement between high-voltage and low-voltage windings, needed for paralleling.

A mechanism that changes the number of active turns in a transformer winding to adjust its voltage ratio, either with the unit de-energized or under load.

A medium-voltage assembly with drawout circuit breakers in separate grounded metal compartments, automatic shutters, and interlocks, built for safe operation and easy breaker removal.

An electronic controller that changes the frequency and voltage fed to an AC motor, adjusting speed and torque while reducing starting current and energy use.

The current an induction motor draws at rated voltage when its shaft is stalled, typically five to eight times full-load current; it is used for protection and voltage-drop studies.

A protective device that senses sustained motor overcurrent, usually thermally or electronically, and opens the control circuit before the motor winding insulation is damaged.

A sectionalized lineup of motor starters, feeders, and protective devices connected to a common bus, used to control and protect many motors from one location.

The order in which the three phase voltages reach their positive peaks; an incorrect sequence reverses a motor's direction, so it must be checked before connecting equipment.

An instrument transformer that reduces line current to a standard secondary value, usually 5 A or 1 A, while isolating meters and relays from the high-voltage circuit.

An instrument transformer that steps high voltage down to a safe, standardized value for meters and relays while preserving an accurate voltage ratio and phase relationship.

The total load in volt-amperes and impedance connected to an instrument transformer secondary; exceeding the rated burden causes ratio and phase-angle errors.

A device that monitors current, voltage, or other quantities and trips a circuit breaker when conditions exceed settings, isolating faults to limit damage and outage scope.

A graph of operating time versus current for a protective device, used to coordinate relays and fuses so the device nearest a fault trips first.

A scheme that compares currents entering and leaving a protected zone and trips when they differ, detecting internal faults while ignoring load and through-fault current.

A DC test using a megohmmeter to measure insulation resistance, revealing moisture, contamination, or deterioration; results are corrected to a standard temperature for comparison over time.

The ratio of insulation resistance measured at ten minutes to the value at one minute; a result below about 2.0 suggests moisture or contamination in the insulation.

An instrument that applies a selected DC voltage, often 250 to 5000 volts, and measures insulation resistance in megohms or higher for cables, motors, and transformers.

A conductive element such as a rod, plate, or building steel in direct contact with earth, providing a low-impedance path to ground for fault and lightning current.

The conductor connecting the metal frames of equipment to the grounding system, giving fault current a low-impedance return path so overcurrent devices open quickly.

The voltage difference between a grounded metal structure a person can touch and the earth underfoot during a ground fault; high values endanger people near substations.

The voltage difference between two points on the earth's surface about one step apart, caused by fault current spreading through soil; it can shock a person walking nearby.

Small localized electrical discharges inside insulation voids or along surfaces, measured to find incipient defects before breakdown; detected with electrical, acoustic, or ultrasonic sensors.

A systematic process that verifies installed systems meet design intent and owner requirements, covering pre-functional checks, functional performance tests, and final documentation.

Testing of equipment at the manufacturer's plant before shipment to confirm it meets specifications, often witnessed by the owner so defects can be fixed off-site.

A documented list of incomplete work or deficiencies found during inspection and commissioning that the contractor must correct before final acceptance and project closeout.

A field test that applies a high voltage above rated to insulation to prove dielectric strength; AC or DC, it can damage aged insulation if voltage is too high.

The comparison of an instrument's reading with a known reference standard and adjustment to reduce error, documented with records traceable to national standards.