NETA ETT Level 3 key terms

The distance from an energized conductor at which a person without appropriate arc-rated protection could receive a second-degree burn from an arc flash. It is calculated from incident energy and is marked on equipment labels.

A shock-protection distance defined in NFPA 70E. Inside the limited approach boundary only qualified persons may enter; inside the restricted approach boundary, shock protection and energized work permits are required.

A state in which the conductor or circuit part has been disconnected from energized parts, locked and tagged, tested to verify absence of voltage, and, if necessary, temporarily grounded and short-circuited.

The amount of thermal energy impressed on a surface at a given distance from an arc, usually expressed in calories per square centimeter or joules per square centimeter. It determines the required arc rating of protective clothing.

Personal protective equipment whose arc rating meets or exceeds the incident energy exposure for the task. Arc rating is expressed in cal/cm² and is determined by standardized fabric testing, not by fabric weight alone.

A documented procedure for isolating energy sources with locks and tags so equipment cannot be re-energized during work. Each worker applies a personal lock, and removal follows a controlled, verified sequence.

Verification with a known-good voltage detector that a circuit is de-energized. The tester is proven on a known live source before and after the test to confirm it is functioning.

The Standard for Electrical Safety in the Workplace, covering safe work practices, arc flash risk assessment, PPE selection, and training requirements for employees exposed to electrical hazards.

The ANSI/NETA Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems. It lists field tests, their purposes, and minimum test values for equipment before it is placed in service.

The ANSI/NETA Standard for Maintenance Testing Specifications for Electrical Power Equipment and Systems. It defines periodic and post-repair field tests used to evaluate whether equipment remains suitable for continued service.

A field test performed on new or newly installed equipment to confirm it was manufactured, assembled, and installed correctly and to establish reference data for future comparison.

Measurements recorded when equipment is known to be in good condition. Later readings are compared against this reference to detect deterioration trends rather than relying on absolute limits alone.

The practice of comparing successive test results over time to detect gradual deterioration. A slowly falling insulation resistance or rising contact resistance is often more meaningful than a single out-of-limit reading.

Accuracy is how close a measurement is to the true value; resolution is the smallest increment the instrument can display. A meter can show many digits of resolution and still be inaccurate.

A measurement method that calculates the equivalent heating value of a waveform, valid for distorted or non-sinusoidal currents. Averaging meters read incorrectly on harmonic-rich loads, so true-RMS capability matters for power-quality work.

The total impedance, including leads and instruments, connected to a current transformer secondary. Excessive burden drives the CT toward saturation and causes ratio and phase-angle errors.

The tendency of insulation to absorb and slowly release charge after a DC voltage is applied. It produces the time-dependent rise in insulation resistance that makes timed readings and the polarization index meaningful.

The DC resistance measured across insulation, usually with an applied voltage of 500 V to 10 kV. It reveals moisture, contamination, and deterioration, and is expressed in megohms or gigohms.

The ratio of insulation resistance at ten minutes to the value at one minute, measured at constant DC voltage. Values below about 1.5 to 2.0 suggest moisture or contamination; higher values indicate dry, healthy insulation.

A terminal on an insulation tester that diverts surface leakage current around the measurement circuit. Using it isolates the true volume resistance of the insulation from surface contamination effects.

A four-wire measurement in which separate current and potential leads eliminate lead and contact resistance from the reading. It is essential for accurate low-resistance measurements below about one ohm.

The DC resistance of a transformer or machine winding, measured to detect loose connections, broken strands, shorted turns, and to provide a baseline for temperature correction and ratio verification.

Adjusting a measured resistance to a standard reference temperature, typically 75 °C for transformers, so results from different test conditions can be compared meaningfully.

A test that applies a known voltage to one winding and measures the induced voltage on another to verify the transformer's ratio. Deviations indicate shorted turns, tap-changer problems, or misconnections.

A single-phase AC test that reveals core problems such as shorted laminations, core faults, or winding shorts by comparing excitation current patterns across phases at a low applied voltage.

A diagnostic method that measures the impedance of a transformer over a range of frequencies. Changes in the response signature can indicate winding deformation, core movement, or mechanical damage from faults or shipping.

The resistance measured across closed breaker or switch contacts, typically in microohms. Rising values indicate pitting, contamination, or loss of contact pressure and can lead to overheating under load.

A test that records contact travel, velocity, bounce, and opening or closing times of a circuit breaker. It verifies the mechanism operates within the manufacturer's specified tolerances and phases are synchronized.

A test, often using a magnetic or high-potential method, that checks whether the vacuum interrupter of a breaker has lost its vacuum and can no longer interrupt fault current reliably.

The ratio of primary current to secondary current, such as 600:5. It must match the connected burden and relay settings so that protective devices see the correct magnitude of fault current.

The current drawn by a current transformer's secondary when rated voltage is applied with the primary open. It indicates core condition and helps confirm the CT will not saturate prematurely.

A device that monitors current, voltage, or other quantities and initiates tripping of a breaker when conditions exceed set thresholds, isolating faults before equipment is damaged.

A test in which a known current or voltage is injected into a relay's input circuits to verify pickup, dropout, timing, and logic. The CT or VT primary circuit is not energized during this test.

A cable test that launches a pulse and analyzes reflections to locate opens, shorts, and impedance changes. The time delay to each reflection is converted into distance along the cable.

Small localized electrical discharges within insulation voids or at surfaces that do not bridge the electrodes. It degrades insulation over time and is detected by acoustic, electrical, or ultrasonic methods.

A protective scheme that detects current flowing to ground through an unintended path and trips the circuit. It is common on services and feeders where low-level arcing faults would not trip standard overcurrent devices.

Voltages that appear across a person's feet or between a hand and feet during a ground fault. Proper grounding grid design limits these voltages to safe levels for personnel near substation equipment.

A method of measuring grounding electrode resistance by driving reference electrodes into the earth and plotting resistance versus probe spacing to find the true resistance plateau.

A test that applies identical surges to each phase of a winding and compares the resulting waveforms. Differences reveal turn-to-turn shorts, ground faults, or phase imbalances in motors and generators.

A technique that examines the frequency spectrum of motor stator current to detect broken rotor bars, eccentricity, and mechanical faults without dismantling the machine.