Free NETA ETT Level 2 Exam Flashcards

The distance from a prospective arc source at which incident energy equals 1.2 cal/cm2, the onset of a second-degree burn on bare skin. Unlike the shock boundaries, it is not looked up by voltage; it is calculated for the specific equipment from available fault current and arc clearing time.

Both are shock boundaries fixed by system voltage in an NFPA 70E table. The limited approach boundary is the outer line an unqualified person may not cross without a qualified escort. The restricted approach boundary is the inner line where increased shock risk requires a qualified person, shock PPE, and a documented plan. NFPA 70E deleted the former third boundary, the prohibited approach boundary, in its 2015 edition.

Category 1 = 4 cal/cm2, Category 2 = 8, Category 3 = 25, Category 4 = 40. The number is the minimum arc rating the whole clothing system must carry, not a severity score for the hazard. If the task exceeds the table's fault-current or clearing-time limits, the PPE category method cannot be used and an incident energy analysis is required instead.

ASTM D120 maximum ac use voltage: Class 00 = 500 V, 0 = 1,000 V, 1 = 7,500 V, 2 = 17,000 V, 3 = 26,500 V, 4 = 36,000 V. OSHA 1910.137 requires in-service gloves to be electrically retested every 6 months, and sleeves and blankets every 12 months. Leather protectors shield the rubber from mechanical damage; they are not the insulation.

Prove the tester on a known live source, test the de-energized conductors phase-to-phase and phase-to-ground, then prove the tester again on the known source. The final proving step is what catches an instrument that failed during the test. The tester must be rated for the voltage and the measurement category of the circuit.

De-energized is not the same as electrically safe. The full sequence is: identify all sources, interrupt the load, open the disconnecting device, visually verify the opening where possible, release stored energy in springs and capacitors, apply lockout/tagout, test for absence of voltage, and apply temporary protective grounds where induced or stored voltage is possible. Skipping any step leaves the circuit merely de-energized.

1910.147 controls hazardous energy during servicing of machines and equipment, but it explicitly does not cover exposure to electrical hazards from work on energized parts. That exposure is covered by Subpart S, 1910.333. Electric utility generation, transmission, and distribution work follows 1910.269 instead. Citing the wrong rule is a common exam trap.

Install only after absence of voltage is verified: ground end first, conductor end last, and remove in the reverse order. Grounds applied at both ends of the work zone create an equipotential zone and drain induced voltage from parallel energized circuits. Grounding only one end leaves the conductor floating and can raise the voltage at the open end through capacitive division.

V = I x R. Power follows as P = V x I, P = I^2 x R, and P = V^2 / R. The I^2R form is the one that matters in testing: doubling the current through a loose joint quadruples the heat generated, which is why a few hundred microhms of extra contact resistance shows up as a thermographic hot spot.

Series: resistances add (Rt = R1 + R2 + ...), current is identical everywhere, and voltage divides in proportion to resistance. Parallel: 1/Rt = 1/R1 + 1/R2 + ..., voltage is identical across every branch, and current divides. Total parallel resistance is always smaller than the smallest branch, which is why a parallel ground path can mask a bad connection.

1 ohm = 1,000 milliohms = 1,000,000 microhms, and 1 megohm = 1,000,000 ohms. Contact resistance is reported in microhms, winding resistance in milliohms, and insulation resistance in megohms or gigohms. Misreading a prefix is the most common arithmetic error on a test report, and it turns a passing result into a failing one by a factor of 1,000.

V_line = sqrt(3) x V_phase, and I_line = I_phase. A 480 V wye system therefore measures 277 V from any phase to neutral (480 / 1.732 = 277). The accessible neutral point is what allows line-to-neutral loads and a system grounding reference.

V_line = V_phase, and I_line = sqrt(3) x I_phase - the mirror image of wye. Delta has no neutral point, so obtaining a ground reference requires a separately derived source, a zig-zag or grounding transformer, or a corner-grounded arrangement.

S = sqrt(3) x V_LL x I_L in volt-amperes, and P = sqrt(3) x V_LL x I_L x PF in watts. The sqrt(3) already converts line-to-line voltage to the per-phase quantity, so substituting line-to-neutral voltage into the same formula double-counts the factor and understates the answer by a factor of 1.732.

Select the test voltage from the equipment's voltage rating using the ANSI/NETA insulation resistance table, not from whatever supply voltage happens to be present. A 600 V class device is tested at 1,000 V dc and a 5 kV class device at 2,500 V dc. Too low a voltage will not stress the dielectric enough to reveal a defect; too high a voltage on low-rated insulation can damage it.

PI = insulation resistance at 10 minutes divided by resistance at 1 minute, taken from one continuous test. Because it is a ratio of two readings at the same temperature, it needs no temperature correction. A PI near 1 means the current never decayed, indicating moisture or contamination. IEEE 43 treats 2.0 as the minimum for modern thermal classes and notes the ratio loses meaning when the 1-minute reading is already very high.

DAR = insulation resistance at 60 seconds divided by resistance at 30 seconds. It is the one-minute screening version of the PI, used when a full 10-minute test is impractical or when the insulation charges so quickly that the PI flattens out. Like PI it is dimensionless and therefore temperature-independent.

Two separate lead pairs are used: one injects the test current, the other senses the voltage drop. Because almost no current flows in the sense pair, test-lead and lead-contact resistance drop out of the reading, which is what makes microhm resolution possible. IEEE C37.09 calls for at least 100 A dc when measuring circuit-breaker contact resistance so a marginal joint is actually loaded.

27 undervoltage, 46 negative-sequence or phase-balance, 49 thermal, 50 instantaneous overcurrent, 51 time overcurrent, 52 ac circuit breaker, 59 overvoltage, 67 directional overcurrent, 86 lockout auxiliary, 87 differential. A suffix names the measured quantity, so 50N is instantaneous ground overcurrent and 51V is voltage-restrained time overcurrent.

The one-line collapses all three phases into a single line and shows the power path, sources, breakers, and ratings. The three-line (ac elementary) shows each phase and each CT and PT secondary separately and is what you use to wire or check a relay. The dc schematic shows trip, close, and control logic contact by contact and is what you use to find why a breaker did not operate.

Three minimums, all at 40 C: 100 megohms for most ac form-wound stator windings built after about 1970; kV + 1 megohms for older windings and all field windings; 5 megohms for random-wound stators, form-wound coils rated below 1 kV,. The kV term is the rated line-to-line voltage in kilovolts, so a 13.8 kV legacy machine needs at least 14.8 megohms.

Insulation resistance falls roughly by half for every 10 C rise, so a warm winding always looks worse than a cool one. Correct the reading before comparing it to a limit or a trend, and know which base you are correcting to: IEEE 43 corrects rotating-machinery readings to 40 C while the ANSI/NETA conversion table references 20 C. Mixing the two bases corrupts a trend.

The guard intercepts surface leakage current and returns it to the instrument without routing it through the measuring circuit. Landing a guard lead on a dirty or damp bushing skirt or cable jacket lets you measure the true volume resistance of the insulation instead of a surface-contamination path, which is why a guarded reading can be far higher than an unguarded one on the same equipment.

A spot reading, usually at 60 seconds, is a quick comparison to a table minimum. A time-resistance test (PI or DAR) watches the curve rise and detects moisture and contamination without needing temperature correction. A step-voltage test raises voltage in steps and looks for a disproportionate drop in resistance, exposing aging, voids, and cracks that a single-voltage reading hides.

a = N1/N2 = V1/V2 = I2/I1. Voltage transforms in direct proportion to the turns while current transforms inversely, so a step-down transformer delivers a higher secondary current than its primary current. Impedance transforms as the square of the ratio, a^2, which is why a small ratio error moves a referred impedance a lot.

ANSI/NETA requires the measured ratio on each tap to be within 0.5 percent of the nameplate or calculated ratio. Test every tap, not just the one in service: a tap-changer contact defect or a shorted turn frequently appears only on positions that are not currently selected, and it will pass unnoticed if only the in-service tap is measured.

With H1 and X1 adjacent and jumpered, a subtractive-polarity unit reads less than the applied primary voltage and an additive-polarity unit reads more. Most power transformers are subtractive; ANSI permits additive polarity on units 200 kVA and smaller with high-voltage ratings of 8,660 V and below. Wrong polarity prevents safe paralleling and inverts a differential (87) scheme so it trips on through current.

With the secondary open, voltage is applied to one high-voltage winding at a time and the magnetizing current is recorded. On a healthy three-legged core the two outer phases read similar and the center phase reads lower, because the center leg has the shorter magnetic path. Shorted turns, core-ground problems, and tap-changer defects break that pattern or produce a large deviation from the sister phase or the prior test.

Very low frequency testing applies ac stress at about 0.1 Hz. A long cable is a large capacitor, so a 60 Hz withstand test would demand an impractically large source; at 0.1 Hz the charging current drops by roughly 600 times, letting a portable set energize the cable while still applying true ac polarity reversal to the insulation.

In XLPE and EPR insulation, dc testing injects space charge that stays trapped and can convert existing water trees into electrical trees. The cable passes the test and then fails in service days or weeks later. Dc withstand remains acceptable on laminated dielectrics such as paper-insulated lead-covered cable, where space charge is not the same problem.

It is the ratio of resistive loss current to capacitive charging current in the dielectric, so it measures how lossy the insulation has become. It is a diagnostic that grades condition and supports trending, not a withstand pass/fail. Rising tan delta as test voltage increases (tip-up) and high scatter between readings both point to water treeing and moisture ingress.

A withstand test such as VLF or dc hipot is go/no-go: the cable either survives the applied voltage for the specified duration or it faults on the spot. A diagnostic test such as tan delta or partial discharge returns a condition number that can be trended and used to rank replacement priority. Withstand answers whether you can energize it; diagnostics answer how much life is left.

MCCBs are sealed, generally not field-maintainable, and normally carry a fixed instantaneous trip. ICCBs are larger, often drawout, add short-time capability, and are only partly maintainable. LVPCBs are fully drawout, field-maintainable, rated for repeated fault interruption, and carry a true short-time withstand rating, which is what lets them be selectively coordinated without an instantaneous element.

A thermal-magnetic unit uses a bimetal that heats for overload plus a magnetic armature for short circuit; its curve is fixed and shifts with ambient temperature. An electronic trip unit reads current sensors and provides adjustable LSIG functions - Long-time, Short-time, Instantaneous, and Ground fault - each with its own pickup and time band, and every dial must match the coordination study rather than a typical value.

Primary injection drives current through the breaker's primary conductors and exercises the entire loop - sensors or CTs, wiring, trip unit, trip coil, and mechanism - which is why it is the commissioning test and the test after any CT or breaker work. Secondary injection feeds a calibrated signal straight into the trip unit and proves only the electronics and their settings; it cannot find a bad CT, an open sensor lead, or a sluggish mechanism.

Measure pole resistance with a micro-ohmmeter at 100 A dc or more; healthy readings usually sit in the tens to low hundreds of microhms. ANSI/NETA calls for investigation when a value exceeds the manufacturer's published data or deviates by more than 50 percent from the lowest reading among adjacent poles. The pole-to-pole comparison catches a bad contact even when no factory value exists.

With the contacts open, an ac or dc overpotential is applied across the gap at the manufacturer's specified voltage; a lost vacuum shows up as breakdown or excessive leakage. An insulation resistance test alone will not detect it. High voltage across an open vacuum gap produces X-rays, so never exceed the specified voltage and keep personnel clear of the interrupter during the test.

A current transformer behaves as a current source driven by its primary. Removing the burden forces the core deep into saturation and develops a lethal peak voltage across the open secondary terminals, destroying CT insulation and relay inputs. Always install the shorting screw or a shorting block across the secondary before lifting any lead.

A potential transformer behaves as a voltage source, so its secondary must never be short-circuited and is normally fused. It also must never be back-fed: applying voltage to the secondary steps it up to full primary voltage on exposed terminals. The mnemonic is CT open equals danger, PT shorted or back-fed equals danger.

A 600:5 CT has a 120:1 ratio, so 300 A of primary current yields 2.5 A of secondary current. Current entering the H1 primary mark exits X1 on the secondary at the same instant. Polarity is what makes directional, differential, and residual-ground connections work, so one reversed CT can make a healthy differential scheme trip on normal through current.

A C400 CT will deliver 400 V to its standard burden at 20 times rated secondary current (100 A) without exceeding 10 percent ratio error; the standard classes are C100, C200, C400, and C800. The class is confirmed in the field by the excitation or saturation test, which locates the knee point where a small voltage increase produces a large jump in excitation current.

A 50 element operates with no intentional time delay once current passes pickup, protecting against high-magnitude close-in faults. A 51 element follows an inverse time-current curve, so the higher the current the faster it operates, which gives downstream devices time to clear their own faults. Coordination is normally built on the 51 curve and time dial; the 50 sets the fast upper limit.

Pickup, the level at which the element just operates; timing at several multiples of pickup checked against the published curve and time dial; target and output contact operation; and an actual trip of the intended breaker. Record as-found values before any adjustment and as-left values after, so the next technician can see whether the relay drifted in service.

Bonding joins metallic parts together to form a low-impedance path that carries fault current back to its source so the overcurrent device operates. Grounding connects the system or equipment to earth to establish a voltage reference and control lightning and static. Earth is a poor fault-current conductor, so bonding clears faults and grounding does not.

The grounded conductor is the neutral: an intentionally grounded circuit conductor that carries normal load current. The equipment grounding conductor carries no current under normal conditions and exists only to carry fault current. Bonding the two together anywhere downstream of the service or the separately derived system puts load current on metal enclosures and raceways.

Fall-of-potential (three-point, 62 percent rule) drives auxiliary current and potential stakes and requires the electrode to be disconnected from the system, giving a true single-electrode resistance. A clamp-on tester measures a loop and needs a parallel return path, so it works on a multi-grounded system without disconnection but returns a meaningless reading on an isolated rod.

Specific gravity indicates the state of charge of the electrolyte and must be temperature-corrected before it is compared; many stationary vented cells are specified at a nominal 1.215 at 25 C. Float voltage is what the charger holds on each cell to offset self-discharge, commonly around 2.17 to 2.25 V per cell depending on plate alloy. Compare both to the manufacturer's published values and the string average, not to a remembered number.

A valve-regulated cell is sealed with immobilized electrolyte, so there is no accessible liquid to draw into a hydrometer. Condition is trended instead with internal ohmic measurements - impedance, conductance, or resistance - compared against that cell's own baseline. IEEE 1188 covers VRLA maintenance and IEEE 450 covers vented lead-acid, and only a discharge test proves actual capacity.

Only after every individual component test in the scope is complete and acceptable. The system function test proves the components interact correctly as a system: a relay pickup actually trips the intended breaker, the right alarm annunciates, and interlocks and permissives behave. Running it early means troubleshooting a system-level symptom that is really an untested component.

As-found values are recorded before any adjustment, cleaning, or re-torquing and document how the equipment was actually operating in service. As-left values are recorded after the work and become the baseline for the next interval. Recording only as-left destroys the trend and hides whether the device had drifted out of tolerance before you touched it.