NETA ETT Level 1 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Limited approach boundary

The distance from an exposed live part within which an unqualified person must not enter unless escorted, and a qualified person must use shock protection.

Arc flash boundary

The distance at which a person without arc-rated protection could receive a second-degree burn, defined as incident energy of 1.2 calories per square centimeter.

Let-go threshold

The current level at which a person can no longer release a conductor, typically around 10 to 20 milliamperes for AC at power frequency.

CAT III rating

A measurement category for test instruments used on distribution circuits and fixed installations, indicating transient withstand beyond that of CAT II.

Four-wire Kelvin measurement

A resistance measurement using separate current and potential leads, eliminating lead and contact resistance so that low winding resistances can be read accurately.

Burden voltage

The voltage drop across a multimeter's internal shunt when measuring current in series, which can disturb the circuit being tested.

Polarization index

Insulation resistance at ten minutes divided by insulation resistance at one minute; values above 2.0 are generally acceptable for Class B insulation and above.

Dielectric absorption ratio

Insulation resistance at sixty seconds divided by the value at thirty seconds; a result below 1.25 suggests moisture or contamination in the insulation.

Guard terminal

A meter connection that diverts surface leakage current around the measurement circuit, allowing true bulk insulation resistance to be read on contaminated surfaces.

Temperature correction of IR

Insulation resistance falls as temperature rises, roughly halving for each ten degrees Celsius, so readings must be corrected to a common base before comparison.

Micro-ohmmeter contact test

A four-wire low-resistance measurement across closed breaker contacts, compared with the manufacturer limit or the previous baseline rather than a universal value.

Trip unit pickup test

A test that slowly raises injected current until the overcurrent element operates, confirming the pickup point is within tolerance of the setting.

Pole discrepancy

The maximum difference in opening or closing time among the poles of a high-voltage breaker, commonly limited to about five milliseconds.

SF6 dew point check

A measurement of moisture in sulfur hexafluoride gas; excessive moisture lowers dielectric strength and can form corrosive byproducts during arcing.

Open CT hazard

An open secondary on an energized current transformer develops a very high voltage that can destroy insulation and injure personnel, so the secondary must never be opened under load.

CT polarity marks

Primary terminals P1 and P2 and secondary terminals S1 and S2 define instantaneous current direction, which differential and directional relays depend on.

VT short-circuit hazard

A shorted voltage transformer secondary draws high current and can destroy the winding, so the secondary must never be short-circuited.

Relay secondary injection

A test that applies currents and voltages to the relay secondary terminals; the primary equivalent is the injected value multiplied by the instrument transformer ratio.

Turns ratio test

A comparison of measured transformer ratio to nameplate ratio; a deviation beyond about half a percent indicates a shorted turn or tap problem.

Winding resistance imbalance

A phase-to-phase difference in transformer winding resistance, commonly limited to two percent, indicating a loose connection or broken strand.

Copper temperature coefficient

Copper resistance rises about 0.4 percent per degree Celsius, so winding resistance readings are corrected to a reference temperature such as 75 degrees Celsius.

Transformer IR test setup

Insulation resistance is measured with the core grounded, testing each winding to ground and between windings, using a DC voltage selected for the winding rating.

Fall-of-potential method

A ground resistance test placing a current probe and a potential probe; the potential probe is set at about 62 percent of the current probe distance.

62 percent rule

For a three-point ground test, the potential probe is placed at 62 percent of the distance to the current probe, with readings checked by moving it ten percent.

Equipment grounding conductor

A conductor that provides a low-impedance fault current path so overcurrent protection operates; it carries no current under normal conditions.

GFCI trip level

A ground-fault circuit interrupter trips at about four to six milliamperes, protecting people rather than equipment, and does not replace equipment grounding.

Time-domain reflectometry

A cable fault locating method that sends a pulse and measures reflection time; distance equals propagation velocity times time divided by two.

Murray loop test

A bridge method for locating cable faults by balancing the faulted conductor against a known good conductor to determine the distance to the fault.

Motor winding balance

A comparison of resistance among motor phases; a difference beyond about five percent suggests a turn-to-turn fault or a poor connection.

Motor IR test voltage

The DC test voltage for motor insulation resistance is selected from the motor's rated voltage, not its horsepower, and the windings must be discharged first.

Test record content

A valid record lists date, ambient temperature and humidity, instrument model and calibration date, test voltage, measured value, and the acceptance limit applied.

Calibration traceability

Instrument calibration must trace to a national standard; an out-of-calibration instrument invalidates acceptance test results and requires retesting.