NETA ETT Level 4 key terms

The voltage difference between two points on the ground surface a stride apart, caused by fault current spreading through earth. It endangers anyone standing near a grounded fault source.

The voltage difference between a grounded metal surface a person touches and the ground under their feet, produced by fault current flowing through the grounding path.

The approach distance at which incident energy from an arcing fault equals 1.2 cal/cm², the onset of a second-degree burn on unprotected skin.

The thermal energy per unit area reaching a surface at a given distance from an arc, usually expressed in cal/cm² and used to select protective clothing.

The maximum incident energy a garment can withstand without the wearer suffering a second-degree burn, determined by standardized arc testing.

A planned procedure that isolates all hazardous energy sources, applies personal locks and tags, and verifies de-energization before work begins.

The closest distance an unqualified or qualified person may approach exposed energized conductors, set by voltage class and shock hazard rather than by arc energy.

Confirming with a tested, rated voltage detector that equipment is de-energized after isolation, checking the tester on a known live source before and after.

The total opposition a circuit presents to alternating current, combining resistance and reactance as a complex quantity measured in ohms.

The opposition to current change from inductance or capacitance, equal to 2πfL for inductors and 1/(2πfC) for capacitors, measured in ohms.

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

The component of AC power that performs useful work, measured in watts and equal to apparent power times power factor.

The power that oscillates between source and reactive elements without doing net work, measured in var and needed to sustain magnetic fields.

The condition where inductive and capacitive reactances cancel at a particular frequency, leaving impedance at a minimum or maximum depending on circuit configuration.

A method of expressing voltages, currents, and impedances as fractions of chosen base values, simplifying transformer and fault calculations across voltage levels.

The current that flows during a fault of negligible impedance, limited only by source and system impedance, used to rate protective equipment.

The maximum short-circuit current a switching device is designed to interrupt safely at a stated voltage, expressed in kiloamperes.

The change in secondary or receiving-end voltage between no-load and full-load conditions, usually expressed as a percentage of rated voltage.

The ratio of insulation resistance measured at ten minutes to that measured at one minute; values near 1 suggest moisture or contamination, values above 2 are generally healthy.

The ratio of insulation resistance at 60 seconds to that at 30 seconds, a shorter test than the polarization index for indicating insulation condition.

The resistance measured across insulation with a DC test voltage, revealing moisture, contamination, and degradation that lower the reading.

A third test lead on an insulation tester that diverts surface leakage current around the measurement circuit so only volume resistance is measured.

An overvoltage test applying AC or DC voltage above rated insulation level for a set time to prove insulation can withstand expected stresses without breakdown.

A measurement comparing primary and secondary winding voltages of a transformer to verify the ratio matches nameplate and that taps are correctly connected.

Measuring DC resistance of each transformer winding to detect loose connections, broken strands, or shorted turns by comparison with other phases and prior data.

Applying voltage to one winding with the others open to measure magnetizing current, revealing core problems such as shorted laminations or winding faults.

A diagnostic that measures transformer impedance over a range of frequencies and compares the trace to a baseline to detect winding deformation or core movement.

Measuring dielectric losses of a transformer bushing, usually by the hot-collar method, to detect moisture or deterioration in the insulation.

A switching device that opens and closes circuits under normal and fault conditions and interrupts short-circuit current without being damaged.

A breaker characteristic ensuring it will open on a trip command even while a close command is maintained, preventing closing into a fault.

A micro-ohmmeter measurement of closed breaker contact resistance, used to detect pitted contacts or poor connections that cause overheating.

The lowest control voltage at which a breaker or its trip coil will reliably operate, verified during functional testing to confirm dependable tripping.

A device that monitors current, voltage, or other quantities and initiates tripping of switching equipment when conditions indicate a fault.

An instrument transformer that produces a secondary current proportional to primary current, allowing relays and meters to measure high currents safely.

The total load, expressed in volt-amperes at rated secondary current, that a current transformer secondary must supply to connected relays and wiring.

The condition where a current transformer core cannot reproduce primary current faithfully, distorting secondary output and risking relay misoperation.

The deliberate time and current grading of protective devices so the device nearest a fault trips first while upstream devices remain closed.

A graph showing how a protective device's operating time varies with current magnitude, used to select settings that achieve coordination.

A cable test that sends a pulse down the cable and analyzes reflections to locate opens, shorts, or impedance changes along its length.

Small localized electrical discharges within insulation voids or at surfaces that erode insulation over time and can be detected by acoustic or electrical methods.

A cable withstand test applying AC voltage at roughly 0.1 Hz, reducing the reactive power needed to stress long cable runs with portable equipment.

The ratio of resistive to reactive current in insulation, indicating dielectric losses; rising values suggest moisture, contamination, or aging.

The resistance measured across insulation with a DC test voltage, revealing moisture, contamination, and degradation that lower the reading.

A motor test applying identical voltage surges to each phase and comparing waveforms to detect turn-to-turn or phase-to-phase winding faults.

Monitoring machine vibration signatures to identify bearing wear, misalignment, imbalance, and looseness before they cause failure.

Analyzing the frequency spectrum of motor current to detect rotor bar defects, eccentricity, and load problems without disturbing operation.

A test applying rated voltage to a machine with the rotor removed or uncoupled to measure core losses and detect insulation faults between laminations.

The voltage rise of a grounding system relative to remote earth during a fault, which drives step and touch potentials.

A method of measuring grounding electrode resistance by injecting current and plotting voltage change against distance to find the resistance plateau.

A conductor, such as a rod or plate, driven into or buried in earth to provide a low-resistance connection to ground.

Detection and tripping of equipment when current leaks to ground through an unintended path, limiting damage and shock exposure.

A protective device that trips when the vector sum of phase currents indicates current returning through ground rather than the intended neutral.

Voltage or current components at integer multiples of the fundamental frequency, expressed as total harmonic distortion and capable of overheating equipment.

A short-duration reduction in RMS voltage, typically caused by faults or motor starting, that can disrupt sensitive loads.

A brief, high-magnitude voltage spike caused by switching or lightning that stresses insulation and can damage electronics.