NETA ETT Level 1 cheat sheet

NFPA 70E approach boundaries for AC: limited approach 10 ft for exposed live parts up to 750 V; restricted approach boundary requires qualified persons and shock protection; arc flash boundary is where incident energy equals 1.2 cal/cm2.

Incident energy is commonly estimated with IEEE 1584 equations; the result depends on bolted fault current, gap, working distance, electrode configuration, and an arcing current that is typically lower than bolted fault current.

Arc-rated PPE categories are replaced by calculated incident energy: arc rating of clothing must equal or exceed the incident energy at the working distance.

Shock hazard is current-driven: roughly 1 mA is perception, 10-20 mA can cause muscular tetany (let-go threshold), and 50-100 mA across the heart can be fatal; body resistance falls sharply with wet skin and higher voltage.

The shock hazard decreases with body resistance and increases with voltage; 120 V can be lethal under the right conditions, so never classify low voltage as safe.

A qualified person must be trained in hazard recognition, use of test instruments, and emergency response including CPR and arc flash first aid; unqualified persons must stay outside the limited approach boundary.

Test instruments must be rated for the environment: CAT III or CAT IV rating for distribution and service entrance work, with voltage rating above the highest transient expected.

De-energized work requires lockout/tagout, verified absence of voltage with a tested instrument, and application of temporary protective grounds where required.

Measurement category defines transient withstand: CAT IV is service entrance/outdoor, CAT III is distribution and fixed installations, CAT II is cord-connected loads, CAT I is electronics; a CAT rating cannot be substituted by a higher voltage rating alone.

Insulation testers apply a DC voltage and measure leakage current; the displayed megohm value equals applied voltage divided by measured current, so a 1 Gohm reading at 500 V corresponds to 0.5 microampere.

Four-wire (Kelvin) measurement eliminates lead resistance and is required for low winding resistances, typically below about 1 ohm, where lead and contact resistance would dominate.

Clamp meters measure current by magnetic field; they cannot measure DC accurately on AC-only models, and a split-core clamp needs the conductor centered and the jaws fully closed.

A multimeter's burden voltage affects current measurements in series; use the highest current range that still gives resolution to reduce heating and loading.

Verify instrument calibration status and battery condition before use; a low battery can produce false insulation readings at high test voltages.

Leads, probes, and clips must be inspected for cracked insulation each use; damaged test leads are a leading cause of arc flash during testing.

Digital low-resistance ohmmeters use a pulsed or reversing DC current to avoid saturating transformer cores during winding resistance measurement.

Insulation resistance is measured after a fixed DC voltage application; IEEE 43 recommends 1 minute for IR and 10 minutes for the polarization index (PI).

PI = IR at 10 minutes divided by IR at 1 minute; a PI below 1.0 indicates poor insulation, 1.0-2.0 is questionable and requires investigation, and above 2.0 is generally acceptable for Class B and higher insulation.

Darlington or dielectric absorption ratio (DAR) = IR at 60 s divided by IR at 30 s; values below 1.25 suggest moisture or contamination.

IEEE 43 minimum IR for AC rotating machines: IR(min in megohms) = kV rating + 1 at 40 C; readings must be corrected for temperature.

IR readings fall with increasing temperature; a rule of thumb is that IR halves for every 10 C rise in temperature, so comparisons require correction to a common base.

Test voltage selection: 500 V DC for equipment rated up to 1000 V, 1000 V for 1000-2500 V equipment, and 2500-5000 V for higher-rated machines, never exceeding the winding's rated test level.

Guard terminals divert surface leakage current around the meter, allowing measurement of true bulk insulation resistance on contaminated or humid surfaces.

After an IR test, the capacitive charge must be discharged through the instrument or a grounding stick before touching conductors.

Contact resistance is measured with a micro-ohmmeter (DLRO) across closed contacts; results are compared to previous baseline or manufacturer limits, not to a universal value.

A contact resistance rise indicates pitting, misalignment, or loose connections; a typical molded-case breaker contact resistance is in the tens to hundreds of microohms.

Insulation resistance of a breaker is measured phase-to-phase and phase-to-ground with the breaker open and again closed; compare to manufacturer or historical values.

Minimum pickup and time-current testing verify the trip unit: apply current and record trip time at each point on the curve, comparing to the published time-current characteristic.

Instantaneous trip test confirms the short-time/instantaneous element operates within tolerance; typical tolerance is plus or minus 10-20 percent of the setting.

For HV breakers, timing tests measure contact opening and closing times and pole discrepancy; a common limit is 5 ms or less between poles, per manufacturer data.

HV breaker insulation tests include power factor/dissipation factor and DC hipot; PF testing detects moisture and contamination that IR alone may miss.

Vacuum bottle integrity can be checked by a magnetic or high-potential test; SF6 breakers require gas density and moisture (dew point) checks before testing.

CT ratio is primary current divided by secondary current; the CT secondary must never be open-circuited under load because the resulting high voltage can destroy insulation and endanger personnel.

CT polarity is marked P1/P2 on the primary and S1/S2 on the secondary; correct polarity is essential for differential and directional relay operation.

A CT burden is the total connected impedance in the secondary circuit including relay, wiring, and leads; excessive burden causes saturation and ratio error.

VT (PT) ratio is primary voltage divided by secondary voltage; the VT secondary must never be short-circuited, because that produces high current and destroys the winding.

Relay test sets inject secondary currents and voltages; the primary equivalent is the injected value multiplied by the CT or VT ratio.

Ratio and polarity checks on CTs and VTs use a primary injection set or a secondary voltage/current source; results are compared to nameplate ratio and polarity marks.

Overcurrent relay pickup is verified by slowly increasing current until the element operates; the measured pickup should be within plus or minus 5 percent of the tap or setting.

Time-current curves follow IEC or IEEE inverse curves; the operating time depends on the multiple of pickup current and the time dial or time multiplier setting.

Turns ratio test compares measured ratio to nameplate ratio; a deviation of more than 0.5 percent (or manufacturer limit) indicates a shorted turn or tap problem.

Turns ratio equals primary voltage divided by secondary voltage, which also equals primary turns divided by secondary turns; for a three-phase transformer, use the correct connection (delta or wye) when computing the ratio.

Winding resistance is measured with a DC source and is temperature-corrected; copper resistance rises about 0.4 percent per degree C, so readings must be corrected to a reference temperature (usually 75 C).

Winding resistance imbalance between phases of more than 2 percent (or manufacturer limit) suggests a loose connection, broken strand, or tap changer problem.

Insulation resistance tests on transformers use 500 V or 1000 V DC for LV windings and 2500 V or higher for HV windings, with the core grounded and windings tested to ground and between windings.

Polarization index and dielectric absorption ratio on transformers detect moisture; low PI with high absolute IR suggests contamination rather than a short.

The transformer must be discharged and grounded after each IR test; residual capacitance can hold a dangerous charge.

Ground resistance is measured by the fall-of-potential method (three-point) or by clamp-on ground testers; the fall-of-potential method places a current probe and a potential probe at defined spacings.

For fall-of-potential, the potential probe should be at about 62 percent of the distance to the current probe; the measurement is valid only if the resistance reading is flat when the potential probe is moved plus or minus 10 percent.

NEC 250.53 requires a single electrode to have 25 ohms or less, or be supplemented by a second electrode; 25 ohms is a maximum, not a design target.

The equipment grounding conductor provides a low-impedance path for fault current so that overcurrent protection operates; it is not a current-carrying conductor under normal conditions.

Bonding connects metal parts to equalize potential; a bonding jumper must be sized per NEC Table 250.122 for the overcurrent device rating.

Ground-fault protection for equipment (GFPE) at service entrances typically trips at a setpoint well below the overcurrent device rating, and the setpoint must coordinate with downstream protection.

Ground-fault circuit interrupter (GFCI) trips at 4-6 mA; it protects people, not equipment, and does not substitute for equipment grounding.

Ground resistance testing should be repeated periodically and after any lightning or fault event; a rising trend indicates corrosion or a broken connection.

Cable insulation resistance is measured phase-to-ground and phase-to-phase with the cable isolated and discharged; compare to historical values and manufacturer limits.

Time-domain reflectometry (TDR) locates cable faults by sending a pulse and measuring the reflection time; distance = velocity of propagation times time divided by two.

Cable fault locating uses the Murray loop or the fall-of-potential method for high-resistance faults; the Murray loop balances a bridge against a known good conductor.

Motor insulation resistance is measured with the motor disconnected and the windings discharged; test voltage is selected from the motor's rated voltage, not its horsepower.

Motor winding resistance should be balanced between phases; a difference of more than about 5 percent suggests a turn-to-turn or connection problem.

Switch and contactor testing includes contact resistance, insulation resistance, and operation timing; a switch that fails to open or close within the manufacturer time indicates a mechanical or control problem.

Motor circuit protection coordination verifies that the overload relay, short-circuit protection, and contactor ratings are compatible with the motor's full-load current and locked-rotor current.

Before any cable or motor test, verify the circuit is de-energized, locked out, and grounded; stored charge in long cables can be lethal.

Test records must include the date, ambient temperature and humidity, instrument model and calibration date, test voltage, and the measured value, because insulation readings depend on all of these.

IEEE 43, IEEE 400, NETA ATS, and NFPA 70E are referenced standards; a report should state which standard and which acceptance limit were applied.

A passing result is defined by comparison to manufacturer data, historical baseline, or the applicable standard, not by a single universal number.

Temperature correction must be applied before comparing insulation or resistance readings to a reference; record the uncorrected value and the correction factor used.

A trend of decreasing insulation resistance or increasing contact resistance across successive tests is more significant than any single reading.

Reports should identify the equipment, the test performed, the pass/fail determination, and any limitations or deviations from the standard procedure.

Calibration traceability to a national standard is required for instruments used in acceptance testing; an out-of-calibration instrument invalidates the result.

When a standard and manufacturer data conflict, the more conservative requirement is normally applied, and the deviation is documented in the report.