ABB HCLD cheat sheet

OSHA 29 CFR 1910.269 approach distances are based on maximum anticipated switching surge and line voltage; minimum approach distance (MAD) increases with voltage class.

Rubber insulating gloves are voltage-rated (Class 00 through Class 4) and must be air-tested and field-checked before each use; test interval is 6 months for gloves in service.

Qualified electrical worker definition requires training in and demonstrated familiarity with construction and operation of equipment and hazards involved, per 1910.269(a)(2).

Arc flash boundary is the distance at which incident energy equals 1.2 cal/cm2; NFPA 70E PPE category is selected from incident energy, not voltage alone.

Step potential decreases with distance from a grounded object; shuffle away with feet together or hop with both feet joined when near a downed conductor.

Ground gradient: touch potential is highest within about 1 m (arm's reach) of a grounded structure; equipotential mat or graded ground reduces it.

Minimum approach distance for 12.5 kV to 15 kV class is typically 2 ft 0 in to 2 ft 1 in; always verify against the current employer table before work.

Two-minute rule: a worker who contacts energized equipment or receives a shock must be removed from duty and medically evaluated before returning.

NESC (IEEE C2) governs supply-line clearances and construction; OSHA 1910.269 governs worker safety practices; both apply and the stricter governs.

NESC vertical clearance for wires over roads is set by voltage and whether the crossing is a highway, street, or railroad; higher voltage requires greater clearance.

NESC Rule 232 covers vertical clearance of wires above ground, roads, rails, and water; Rule 234 covers clearance of wires from buildings and other structures.

29 CFR 1910.269 requires annual inspection of rubber protective equipment and 6-month electrical testing for gloves and sleeves.

Pole loading is governed by NESC Grade B or Grade C construction; Grade B requires higher safety factors (typically 4 for Grade B, 2.5 for Grade C for pole strength).

ANSI C2/NESC requires that lines be designed for the 50-year return wind/ice loading in the applicable district loading map.

Lockout/tagout for distribution is under 1910.269(d); the tag must identify the employee and the equipment, and only the applying employee may remove it.

Grounding for the protection of employees is under 1910.269(p); temporary protective grounds must be sized to carry available fault current and installed with a shotgun or hot stick from a safe position.

Ohm's law: V = I x Z; three-phase power: P = √3 x VLL x I x PF; single-phase: P = V x I x PF.

Per-unit impedance converts to ohms by Z(ohms) = Z(pu) x Z(base), where Z(base) = kV^2/MVA for three-phase.

Delta-wye transformer bank: primary line current = √3 x phase current; line-to-line secondary voltage = √3 x phase voltage.

Voltage drop on a feeder: VD ≈ I x (R cosθ + X sinθ) x length; for three-phase multiply by √3.

Fault current from a transformer: Isc ≈ kVA x 1000 / (√3 x VLL x Z%); a 5% impedance transformer yields about 20x rated current on a bolted fault.

Power factor correction: kVAR required = kW x (tan θ1 − tan θ2), where θ1 and θ2 are the before and after power-factor angles.

Skin effect and proximity effect increase AC resistance above DC resistance; ACSR and AAAC conductors are selected by ampacity and sag, not just resistance.

Symmetrical components: positive, negative, and zero sequence; zero-sequence current flows only in grounded systems and requires a ground return path.

Pole class and length: ANSI O5.1 class 1 through 5; a Class 3 pole of 40 ft has a specified circumference at 6 ft from butt and a rated load at 2 ft from top.

Sag increases with temperature and with span length; sag-tension is set from stringing tables for the ruling span, not the individual span.

Conductor tie-in: preformed ties, armor rods, and clamp-top insulators distribute side load; armor rods protect against chafing and vibration.

Guy leads should be installed at an angle of 45 degrees to the pole where practical; a guy at 45 degrees carries about 1.41 times the horizontal load.

Anchor holding capacity depends on soil class; a screw anchor in Class 4 soil may need a larger anchor or a log anchor to develop the required pull.

Minimum pole setting depth is typically 10% of pole length plus 2 ft; check local standards.

Crossarm and insulator placement: phase spacing is set by voltage; 15 kV class typically uses 8 ft to 9 ft crossarms with 10 in to 12 in insulators.

Conductor clearance to the neutral and to other conductors is set by NESC Table 235-5 for the voltage class and span length.

Cable ampacity depends on soil thermal resistivity, burial depth, duct bank configuration, and ambient earth temperature; deeper burial reduces ampacity.

Concentric neutral cable: neutral carries unbalanced current and fault current; the semicon layers equalize the electric field and must be terminated correctly.

Cable pulling tension: T = L x w x f (straight pull) or use a tension calculator for bends; sidewall pressure at bends is the limiting factor.

Minimum bending radius for solid dielectric cable is typically 8x to 12x the cable diameter; exceeding it damages insulation and semicon.

Faulted circuit indicator and cable identification: cable tags and phase identification must be verified by a phasing set before energizing.

Pad-mounted transformer clearances to buildings and the public are set by NESC and local codes; front clearances are typically 10 ft for operation.

Grounding: URD cable concentric neutral is grounded at both ends and at each transformer; neutral-to-earth voltage is checked before work.

Cable fault locating: time-domain reflectometry (TDR) locates opens and low-resistance faults; a thumper locates high-resistance faults by acoustic and electromagnetic detection.

Wye-wye transformer: neutral must be solidly grounded; a floating neutral causes voltage imbalance and overvoltage on one phase.

Delta-delta bank: one transformer can be removed and the bank operated in open-delta at reduced capacity (about 58% of the three-transformer bank).

Open-delta capacity: kVA of open-delta bank = √3 x kVA of each transformer; two 50 kVA units give about 86.6 kVA.

Additive vs subtractive polarity: subtractive transformers have H1 and X1 adjacent; additive have H1 and X1 diagonally opposite. Most distribution transformers are subtractive.

Paralleling transformers requires matched voltage ratio, impedance, and tap settings; mismatched impedance causes circulating current.

Taps: a ±5% two-position or four-position tap changer adjusts the primary turns to compensate for primary voltage variation.

Wye-grounded primary to delta secondary is not permitted on four-wire multi-grounded primary systems because it provides a path for zero-sequence current and ferroresonance.

Transformer losses: no-load (core) loss is constant; load loss varies with the square of the load current; efficiency peaks when these losses are equal.

Recloser vs fuse: reclosers clear temporary faults with multiple operations; fuses are one-shot and coordinate by time-current curves.

Coordination: the protective device nearest the fault should operate first; time-current curves must not cross within the fault current range.

Sectionalizer counts fault-current interruptions and opens on the last count; it has no fault-interrupting rating and must be backed by a recloser or breaker.

Recloser sequence: typically two fast and two delayed operations; the fast curve protects people and equipment, the delayed curve allows downstream fuses to clear.

Ground-fault protection on four-wire systems uses a zero-sequence CT or residual connection; set above normal unbalanced load and below the minimum arcing fault current.

Switching order: open the load-break device, verify de-energized, apply protective grounds, then tag; restore in reverse order.

Fault current is limited by source impedance; available fault current at the transformer secondary is highest at the terminals and decreases with distance along the feeder.

Automatic reclosing is blocked when the circuit is being worked or when a fuse-saving scheme would re-energize a faulted section.

Insulation resistance test (megohmmeter): apply for 1 minute and 10 minutes; the polarization index (10-min/1-min) should exceed 2.0 for good insulation.

Transformer turns ratio (TTR) test verifies winding ratio and polarity; a deviation of more than 0.5% from nameplate indicates a problem.

Winding resistance test: measure each phase and compare; a difference of more than 2% between phases indicates a loose connection or shorted turns.

Transformer oil testing: dissolved gas analysis (DGA) detects arcing, overheating, and corona; moisture and breakdown voltage tests verify dielectric strength.

Power factor/dissipation factor test on bushings and windings detects insulation contamination and moisture; a rising trend is more significant than a single reading.

Cable hipot and VLF testing: VLF at 0.1 Hz is used for acceptance and maintenance of solid dielectric cable; DC hipot is not recommended for XLPE.

Ground resistance test: fall-of-potential method with a 62% distance rule; a ground grid should measure below the specified ohms (commonly 5 ohms or less at substations).

Commissioning checklist: verify nameplate, ratio, polarity, phase rotation, and grounding before energizing; perform a phasing check across open points.

Voltage complaints: check primary voltage at the transformer, tap setting, and secondary voltage under load; a low reading may be an open neutral or a bad connection.

Blown fuse on one phase of a wye-wye bank causes low voltage on that phase and neutral shift; a delta bank loses capacity and causes voltage imbalance.

Repeated fuse blowing indicates a persistent fault, an undersized fuse, or a fault on the service; do not upsize the fuse to stop the blowing.

Neutral-to-earth voltage above a few volts indicates a poor neutral connection or a bad ground; check the service neutral and grounding electrode.

Motor single-phasing: a three-phase motor on one blown fuse will not start and will overheat; check all three phases before replacing the fuse.

Transformer noise or overheating: check for overload, low oil level, loose connections, or a shorted turn; a hot transformer with normal load indicates internal fault.

Open conductor on a three-phase line causes voltage imbalance and possible single-phasing of customers; use a phasing set and voltage readings to locate.

Fault current indicators and recloser operation counters help locate faults; a recloser that locks out after multiple operations indicates a permanent fault.

Fault types: single line-to-ground is most common (about 70% to 80% of faults); line-to-line, double line-to-ground, and three-phase are less frequent.

TDR (time-domain reflectometry): pulse travels at about 0.5c to 0.7c in cable; distance = (velocity of propagation x time)/2.

Thumper (surge generator): applies a high-voltage pulse to break down the fault; the acoustic and electromagnetic signals locate the fault point.

Faulted circuit indicators (FCIs) indicate passage of fault current; they must be reset after the fault is cleared to indicate the next fault.

Restoration sequence: isolate the faulted section, restore as much load as possible from the source, then repair and re-energize the isolated section.

Sectionalizing: open the sectionalizer or switch nearest the fault, close the source breaker, then progressively test sections to locate the fault.

Ground fault on a four-wire system: check the neutral and grounding connections; a broken neutral causes overvoltage on one phase.

Fault current magnitude decreases with distance from the source; comparing measured fault current to calculated values helps locate the fault.

Hot sticks (insulated tools): fiberglass-reinforced plastic; test electrically every 2 years and inspect before each use for cracks, moisture, and contamination.

Rubber insulating gloves and sleeves: air test before each use; electrical test every 6 months; store in a canvas bag away from sunlight and heat.

Bucket truck: insulated boom and bucket; dielectric test annually; maintain minimum approach distance and use a bucket liner and cover-up.

Voltage detectors: test on a known live source before and after use; a tester that fails the before/after check is unreliable.

Phasing set: verifies phase relationship across an open point; both sides must be energized and the set rated for the voltage.

Grounding sets: temporary protective grounds must be sized for fault current and installed with a shotgun stick from a safe position; never ground a conductor while a worker is in contact with it.

Handline and tie tools: use a handline rated for the load; never exceed the working load limit; inspect rope for cuts and glazing.

Cover-up: insulating blankets, line hose, and hoods are rated by voltage class; inspect before use and do not use damaged cover-up.