NETA ETT Level 1 key terms

The approach limit distance from exposed energized conductors at which a person could receive a second-degree burn from an arc flash. It is calculated from incident energy analysis or the arc flash PPE category tables.

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-rated PPE.

A shock protection boundary that unqualified persons must not cross unless escorted by a qualified person. Only qualified persons may cross it, and only with appropriate shock protection measures.

A shock protection boundary that only qualified persons may cross, and only while wearing shock-protective equipment and using insulated tools. It lies closer to exposed energized parts than the limited approach boundary.

Clothing and equipment assigned an arc rating, such as calories per square centimeter, that indicates its resistance to thermal energy from an electric arc. Arc rating differs from flame resistance because it quantifies withstand energy.

A formal procedure for de-energizing, isolating, locking, and tagging equipment so it cannot be re-energized while work is performed. Each worker applies a personal lock, and the equipment is verified de-energized before work begins.

The step of testing a circuit with a known-good voltage detector to confirm it is de-energized before grounding or touching conductors. The tester is proven on a known live source before and after the test.

The risk of electric current passing through the body because of contact with energized parts or inadequate insulation. It is managed through isolation, grounding, distance, and shock-protective equipment rather than arc-rated clothing alone.

A device used to verify the presence or absence of voltage on a conductor. It must be rated for the system voltage, tested on a known source before and after use, and checked for function.

A multimeter that measures the root-mean-square value of a waveform by sampling and computing it, so it reads non-sinusoidal currents and voltages correctly. Average-responding meters can be significantly wrong on distorted waveforms.

The ratio of a waveform's peak value to its RMS value. A pure sine wave has a crest factor of about 1.414, and meters are rated to a maximum crest factor beyond which readings become inaccurate.

An instrument that measures current by surrounding a conductor with a magnetic core and sensing the induced field. It measures current without breaking the circuit and must be rated for the system voltage and frequency.

A clamp meter that senses the magnetic field with a semiconductor sensor, allowing measurement of both AC and DC current, including DC current in a conductor without breaking the circuit.

A portable source of known voltage used to verify that a voltage detector or tester is functioning before and after an absence-of-voltage check. It substitutes for a known live source when none is available.

A safety classification for test instruments indicating the transient overvoltage environment in which they may be used. CAT III covers distribution-level circuits and CAT IV covers service entrances and utility connections.

A test that applies a DC voltage across insulation and measures the resulting resistance, indicating moisture, contamination, or deterioration. Results are read after a defined electrification time, typically one minute.

The ratio of insulation resistance measured at ten minutes to the value measured at one minute, using the same test voltage. It indicates insulation condition independent of temperature and size, with values above 2.0 generally considered acceptable.

The ratio of insulation resistance at sixty seconds to the value at thirty seconds. It is a faster indicator of insulation condition than the polarization index and is useful when a ten-minute test is impractical.

A terminal on an insulation tester that diverts leakage current across the insulation surface away from the measurement circuit. Using it removes surface contamination effects and gives a truer reading of internal insulation resistance.

Current that flows along the outside surface of insulation because of moisture or contamination rather than through the insulation volume. It can falsely depress insulation resistance readings and is reduced by cleaning or guarding.

An overvoltage test that stresses insulation above normal operating voltage for a defined time to confirm it can withstand the electrical field. It is a pass/fail proof test, not a diagnostic measurement like insulation resistance.

A high-potential test that applies an elevated AC or DC voltage to insulation to verify dielectric strength. It is a pass/fail proof test that can damage deteriorated insulation, so it follows insulation resistance testing.

A test that injects a DC current through closed breaker contacts and measures the voltage drop to calculate resistance in micro-ohms. It reveals pitted contacts, loose connections, and poor contact pressure.

A common name for a low-resistance measurement of breaker contacts or busbar joints using a micro-ohmmeter, typically injecting 100 A or more DC. Results are compared with previous baseline values rather than a single absolute limit.

The component of a low-voltage circuit breaker that senses current and initiates tripping, providing long-time, short-time, instantaneous, and ground-fault protection functions. Its settings must match the coordination study.

A test in which current is injected through the breaker's main current path to verify the entire tripping system, including current sensors and trip unit. It confirms performance that secondary injection alone cannot.

A test that injects a simulated current or voltage signal into the relay or trip unit's secondary terminals to verify its logic and settings. It does not prove the current transformers or trip coil circuit.

A graph plotting trip time against current for a protective device, showing its long-time, short-time, and instantaneous regions. Curves of series devices are compared to confirm selective coordination.

The arrangement of protective devices so that the device nearest a fault trips first, limiting the outage to the smallest affected section. It is verified by comparing time-current curves and pickup settings.

A device that monitors current, voltage, or other quantities and initiates a trip when conditions exceed settings. It is tested by secondary injection to verify pickup, timing, and output contacts.

An instrument transformer that steps primary current down to a standard secondary level, typically 5 A or 1 A, for metering and relaying. Its polarity and ratio must be verified before protective settings are applied.

An instrument transformer that steps high voltage down to a standard secondary value, typically 120 V, for metering and protection. Its ratio and burden must be correct for accurate measurement.

A test that confirms the current transformer's turns ratio and the relative polarity of its secondary terminals. Correct polarity is essential so differential and directional relays see currents in the proper direction.

The total impedance connected to an instrument transformer's secondary, including wiring, relays, and meters. Excessive burden causes ratio and phase-angle errors and can saturate a current transformer.

A test that applies a known voltage to one winding of a transformer and measures the induced voltage on another to confirm the winding ratio. Results are compared with nameplate ratio to detect shorted turns.

A DC measurement of each winding's resistance, used to detect loose connections, broken strands, or shorted turns. Readings are corrected to a reference temperature and compared between phases and with prior results.

A test that applies AC voltage to one winding with the others open and measures the current drawn, revealing core condition and shorted turns. Results are compared phase-to-phase and with previous tests.

The adjustment of measured resistance or insulation values to a standard reference temperature, commonly 20 degrees Celsius for insulation and 75 degrees Celsius for winding resistance, so results are comparable.

A conductive element, such as a rod, plate, or pipe, in direct contact with the earth that provides a path to ground. Its resistance is measured to confirm it meets the installation requirements.

The intentional electrical connection of metallic parts to ensure they remain at the same potential, preventing dangerous voltage differences. It is distinct from grounding, which connects to earth.

A method of measuring grounding electrode resistance by driving reference stakes and measuring voltage drop as the current stake is moved. The resulting curve confirms the true resistance plateau.

A test that measures the resistance of a grounding conductor loop without disconnecting it, by inducing a voltage and sensing the resulting current. It requires a parallel ground path to be valid.

A protective scheme that detects current flowing to ground outside the intended path and trips the circuit to limit damage and shock. It is tested by injecting a simulated ground-fault current.

A test that applies insulation test voltage in steps and plots resistance against voltage to reveal insulation weaknesses that a single-voltage test might miss. A falling resistance trend indicates deterioration.

A set of tests on a motor branch circuit covering winding insulation resistance, winding resistance, and supply cable condition. Results help distinguish motor faults from cable or starter faults.

A test that applies identical voltage surges to each motor winding and compares the resulting waveforms to detect turn-to-turn or phase-to-phase insulation faults. It is used on motors and coils.

A documented set of measurements, conditions, and instrument details captured during a test. It must include ambient temperature, humidity, test voltage, and instrument identification so results can be reproduced and compared.

The initial or previous set of test results against which later measurements are compared. Trending detects gradual deterioration that a single pass/fail limit might not reveal.

The specified limits or conditions a test result must meet to be considered passing, taken from standards, manufacturer data, or engineering specifications. They must be cited in the test report.