NETA ETT Level 2 key terms

The distance from energized equipment at which a person could receive second-degree burns from an arc flash. It is calculated from incident energy and marks where arc-rated protective equipment becomes mandatory.

The amount of thermal energy per unit area, usually stated in calories per square centimeter, that reaches a surface during an arc flash. It is used to select clothing and equipment with adequate arc ratings.

A shock-protection boundary set at a distance from exposed live parts where only qualified persons, or unqualified persons under escort, may proceed. Shock protection and hazard awareness are required inside it.

A closer shock-hazard boundary around exposed live parts that only qualified persons may cross, using appropriate shock protection and usually an energized work permit.

A formal procedure for de-energizing equipment, isolating every energy source, applying locks and tags, releasing stored energy, and verifying a zero-energy state before work starts.

Connecting all conductors and nearby grounded metal together with temporary protective grounds so the entire work area sits at one potential and no dangerous voltage difference can appear across a worker.

The voltage difference between two points on the earth's surface roughly one step apart, created when fault current spreads outward through the soil from a grounded or fallen conductor.

The voltage difference between a person's hand resting on a grounded metal object and their feet standing on the earth, caused by fault current flowing through the grounding path.

Clothing and equipment tested to a stated arc thermal performance value, marked in calories per square centimeter, that gives a known level of protection against arc flash heat.

A worker who has demonstrated the skills and knowledge needed to work safely on or near energized electrical equipment and who is trained to recognize and avoid the associated hazards.

The closest distance a qualified worker may bring any part of the body, tool, or test lead to an exposed energized conductor, determined by system voltage and required shock protection.

The relationship stating that voltage equals current multiplied by resistance in a DC circuit, or by impedance in an AC circuit, so any one value can be calculated from the other two.

The ratio of real power in watts to apparent power in volt-amperes in an AC circuit. It runs from zero to one and shows how much of the current performs useful work.

The total opposition an AC circuit offers to current flow, combining resistance and reactance. It is measured in ohms and treated as a phasor quantity with magnitude and angle.

The principle that the total current entering a junction equals the total current leaving it, since charge cannot pile up at a node. It underpins circuit analysis and current measurements.

A drawing that represents alternating voltages and currents as vectors rotating together, making their magnitudes and phase relationships visible so they can be compared and combined graphically.

The ratio of primary winding turns to secondary winding turns, which equals the primary-to-secondary voltage ratio in an ideal transformer and varies inversely with the current ratio.

Power supplied by three sinusoidal voltages displaced 120 degrees apart, which delivers constant power to a balanced load and is calculated as the square root of three times line voltage times line current times power factor.

A simplified drawing that uses single lines and standard symbols to show how power flows through generators, transformers, breakers, buses, and protective devices in a system.

An instrument that applies a high direct voltage to insulation and measures the tiny resulting current, calculating and displaying insulation resistance in megohms or gigohms.

The ratio of insulation resistance measured at ten minutes to the value at one minute. A result near or above 2.0 generally indicates dry insulation in acceptable condition.

The ratio of insulation resistance at sixty seconds to the value at thirty seconds. It is a short version of the polarization index used to flag moisture and contamination.

A four-wire instrument that injects a known direct current and measures the very small voltage drop produced, reading low resistances such as breaker contacts and bus joints in microhms.

A resistance technique that uses two current-carrying leads and two separate voltage-sensing leads, canceling lead and contact resistance so very low values can be read accurately.

The ratio, expressed as a percentage, of resistive current to capacitive current through insulation at a test voltage. Rising values point to moisture, contamination, or aging.

Small localized electrical discharges inside insulation voids or along surfaces that do not bridge the electrodes. They slowly erode insulation and are found with acoustic or electrical sensors.

A meter function that computes the heating-equivalent value of a distorted waveform instead of assuming a pure sine wave, so harmonic-rich circuits are measured correctly.

A method of measuring earth resistance by driving a current probe and a potential probe into the ground at set spacings and comparing the voltage drop with the injected current.

Using a thermal imaging camera to compare temperatures on energized equipment, where abnormal heating reveals loose connections, overloads, or failing components before failure occurs.

Measuring the DC resistance of transformer or motor windings and comparing phases or earlier readings to uncover opens, shorts, poor connections, or turn-to-turn faults.

Applying a known AC voltage to one transformer winding and measuring the induced voltage on another to confirm the ratio and detect shorted turns or incorrect tap settings.

Comparing a transformer's impedance signature across a range of frequencies with a baseline record to detect winding deformation, displacement, or core damage after a fault or during shipping.

Recording contact travel against time during a trip or close operation and comparing the curve with manufacturer data to judge operating speed, damping, and mechanical condition.

Applying a specified high AC or DC voltage above normal operating level for a set period to prove that insulation can endure it without breakdown or excessive leakage.

A quick, non-destructive check that applies a small AC signal to a battery and estimates internal resistance and available capacity without discharging the battery.

The resistance measured across mated breaker or switch contacts, which increases with pitting, corrosion, or misalignment and causes overheating when the equipment carries load.