Full step-by-step calculations with standard clause references at every stage โ 59 examples so far, growing toward at least one per calculator. Every number is generated by the calculator's own verified engine, not hand-typed.
IDMT relay coordination and grading, differential and earth-fault protection, arc flash, breaker/fuse sizing, and generator paralleling/fault contribution.
Two IEC Standard Inverse relays look correctly graded at one fault current โ until the full-range sweep reveals the margin collapses at higher currents.
Read the worked example โAn earth-fault relay with both an inverse-time (51N) stage and a high-set instantaneous (50N) stage, checked at two different fault levels.
Read the worked example โA load-end, mid-feeder and source relay all see the same fault โ checking whether each step up the chain has enough time separation from the one below it.
Read the worked example โThe same dual-slope 87T characteristic correctly restrains through normal load with CT mismatch, then trips decisively for a genuine internal fault.
Read the worked example โUsing the classic Base kVA Method to estimate available short-circuit current at two points down a radial LV network, and checking a downstream breaker's interrupting rating against it.
Read the worked example โA routine incident-energy calculation for a low-voltage motor control centre โ and why a result that's barely above one PPE threshold still requires the next full category up.
Read the worked example โTwo different sizing rules in the same calculator โ a general continuous/non-continuous load, and a motor branch circuit sized for starting-current withstand instead of running current.
Read the worked example โThe three checks a synchroscope or sync-check relay makes before it's safe to parallel an incoming generator with a live bus.
Read the worked example โTwo identical 500 kVA gensets running in parallel โ how much fault current does each one contribute to a common bus fault, and what does that mean for switchgear rating?
Read the worked example โCable and conductor sizing, fill and pulling calculations, and overhead/distribution line voltage regulation and losses.
A 50 kW/415 V feeder where the smaller cable that looks fine on paper actually fails the ampacity check โ and the next size up clears both checks comfortably.
Read the worked example โInstead of looking up a table value, this calculator solves the IEC 60287 thermal circuit directly โ the same method behind CIGRE's own published verification cases.
Read the worked example โSix THHN conductors in 3/4-inch EMT pass with plenty of room to spare โ enough room that a smaller, cheaper conduit would technically work too.
Read the worked example โA 12-inch ladder tray loaded with smaller power cables only, checked against the area-based fill rule for cables under 4/0 AWG.
Read the worked example โTension and sidewall pressure both pass comfortably for this pull โ but the jam ratio lands right inside the danger band, the one check that actually fails.
Read the worked example โAn 800 m HART loop checked against the host system's total capacitance limit โ and how much further the same cable could actually run before capacitance becomes the constraint.
Read the worked example โUsing the conductor's own R and X per kilometre to find how much voltage a rural 11 kV feeder loses over 5 km of overhead line.
Read the worked example โConverting a feeder's peak load and load factor into an annual energy-loss estimate โ without needing a full year of interval load data.
Read the worked example โEarthing grid design, lightning protection and rolling sphere method, touch voltage, and static/ESD hazard checks.
A 30m x 20m grid with a perfectly reasonable-looking resistance and GPR still fails the actual touch and step voltage safety checks by a wide margin.
Read the worked example โRunning the full risk-of-loss-of-life calculation for a modest warehouse finds the risk is already below the tolerable threshold โ no LPS is strictly required by the standard's own numbers.
Read the worked example โA simple geometric check โ how far from the base of a 10 m mast does an IEC 62305 Class III lightning protection zone actually extend?
Read the worked example โA modest 15 A imbalance current through a 2 ฮฉ ground path produces a touch voltage that comfortably clears the IEC 60364-4-41 dry-location limit.
Read the worked example โThe same NFPA 77 threshold, applied to two very different real-world bonding-clip readings โ one a clean pass, one a clear failure needing immediate attention.
Read the worked example โA modest 100 pF part charged to 10 kV โ a completely plausible static charge in an industrial process โ stores twenty times the minimum ignition energy of a typical hydrocarbon atmosphere.
Read the worked example โTransformer, CT, VT and busbar sizing/rating, plus insulation resistance and polarization index condition tests.
A 400/1 A protection CT with a 150 V knee point, checked against the required knee-point voltage for its stated accuracy limit factor โ and what happens to its output once the fault current exceeds that limit.
Read the worked example โAn 11 kV phase-to-earth VT feeding a relay and a meter โ sized to a standard VA rating that keeps it loaded in the specific percentage window where accuracy class is actually guaranteed.
Read the worked example โAn 800 kW load with growth margin, hot-climate derating, and full N-1 redundancy โ each of the two installed transformers has to be able to carry the entire load alone.
Read the worked example โTwo independent generator-sizing checks โ steady running capacity and motor-starting voltage dip โ with running load turning out to be the larger, governing requirement in this case.
Read the worked example โA 1000 kVA transformer's own open-circuit and short-circuit test results, used to find its full-load efficiency, the loading point where efficiency actually peaks, and its voltage regulation at rated load.
Read the worked example โA 100 x 10 mm copper busbar carrying 1200 A, checked by solving the actual heat balance between IยฒR loss and convective/radiative cooling โ not a table lookup.
Read the worked example โTwo related IEEE 43 condition-assessment checks on the same winding โ a minimum-IR pass/fail and a polarization index that clears its minimum by a much narrower margin.
Read the worked example โTwo windings with a similarly adequate 1-minute IR reading โ one develops a strong polarization trend over the 10-minute test and passes comfortably, the other barely rises and fails outright.
Read the worked example โPower factor correction, harmonics, demand studies, voltage/load balance, unit conversion and tariff estimation.
A 500 kW load running at a costly 0.75 power factor โ sized up to a 277 kVAr delta-connected capacitor bank that cuts line current by a fifth.
Read the worked example โA 400 V bus with a real-world harmonic spectrum, checked against both the voltage distortion limits (Table 1) and the load-referenced current distortion limits (Table 2) โ passing both, with the fifth harmonic as the closest call.
Read the worked example โFour load categories, each with its own demand factor, combine into a diversified maximum demand that's meaningfully lower than simply adding up connected load.
Read the worked example โA modest 1.5% voltage unbalance between three phases โ well under the 5% NEMA ceiling, but still enough to call for a small motor derating.
Read the worked example โThree unevenly loaded phases in a distribution board โ computing the resulting neutral current directly from the phasor relationship, not just estimating it as the difference between the busiest and quietest phase.
Read the worked example โStarting from real power and power factor alone, the complete AC power triangle for a 415 V three-phase load โ apparent power, reactive power and current, all in one pass.
Read the worked example โPeak and off-peak energy, a demand charge, and a below-threshold power factor all combine into one monthly bill โ with the PF penalty adding a small but real surcharge.
Read the worked example โMotor branch-circuit sizing, motor protection, and VFD energy savings.
A 25 HP motor's branch circuit sized entirely off its NEC table full-load current, not nameplate โ plus checking the voltage dip its direct-on-line start produces at the site's short-circuit capacity.
Read the worked example โThree independent protection settings for the same motor โ overload trip class chosen from its starting time, contactor size from its duty, and ground-fault pickup from the system's earthing arrangement.
Read the worked example โA 75 kW pump motor, currently running throttled at reduced flow โ the affinity laws show why VFD speed control saves dramatically more energy than a valve ever could.
Read the worked example โBattery sizing, UPS sizing, emergency power sequencing, genset fuel, and energy storage (BESS).
The IEEE 485 section method correctly sizes battery capacity for a four-period duty cycle โ but the resulting cell count doesn't actually keep the string above its minimum discharge voltage.
Read the worked example โA 200 kW critical load, sized to a standard UPS frame with full N+1 redundancy โ plus how much battery energy a 15-minute ride-through actually needs.
Read the worked example โThis NFPA 110 Type 10 system's generator actually takes 11.8 seconds to be ready โ 1.8 seconds over its own Type 10 target โ but the UPS bridge easily covers the gap.
Read the worked example โA straightforward but essential check โ how long a 500 L tank actually keeps a generator running, and what that costs per hour.
Read the worked example โA 100 kW, 2-hour backup requirement sized up to nameplate battery energy, checked against C-rate and PCS voltage window, and carried through to an actual AC cable size.
Read the worked example โ4-20mA loop budgets, intrinsic safety, thermocouple/RTD conversion, and fire & gas loop power.
A 24 V loop-powered transmitter at the far end of a 1000-foot run โ checking it still gets enough terminal voltage at the worst-case 20 mA signal, and how much farther the same wire gauge could actually reach.
Read the worked example โEvery basic entity-concept parameter checks out for this barrier and field device pairing โ until a realistic 500 m cable run pushes total capacitance over the barrier's limit.
Read the worked example โA K-type thermocouple reading corrected for its cold junction, and the same raw Pt100 resistance interpreted three different ways depending on wiring configuration.
Read the worked example โA ten-detector initiating device circuit, checked in both its quiet standby state and its worst-case alarm state โ both comfortably clear the minimum operating voltage.
Read the worked example โSolar PV string/inverter sizing and EV charge point sizing โ with room to grow as more renewables tools ship.
A common-looking 550 Wp module and a 10 kW three-phase inverter, checked against IEC 62548's string voltage window and per-MPPT current limit โ string length and module current turn out to be two completely separate problems.
Read the worked example โOne 32A Mode 3 charge point, a common earthing mistake the calculator catches automatically, and how a Load Management System can roughly halve a 10-point site's feeder size.
Read the worked example โHVAC electrical sizing, lighting design, elevators, data-center PUE, life-cycle cost, and heat management.
NEC Article 440 branch-circuit sizing for one compressor motor, then the same compressor paired with a condenser fan on a shared feeder โ showing why combination-load sizing isn't just 'add the two MCAs together'.
Read the worked example โThe same EN 12464-1 lumen-method formula applied to a 500 lux interior office and a 75 lux exterior car park traffic route โ two very different target illuminances driving two very different fixture counts.
Read the worked example โOne traction elevator's motor power from its rated load, speed, and counterweight balance, then the NEC Table 620.14 demand factor that lets a shared four-elevator feeder be sized well below the sum of all four running flat-out.
Read the worked example โA facility drawing 1,500,000 kWh against 1,000,000 kWh of IT load lands on a PUE of exactly 1.5 โ and the classification rule's strict less-than comparison puts it in the band below where a casual reading might expect.
Read the worked example โA $18,000 higher upfront cost for premium-efficiency equipment, evaluated against its lower annual operating cost over 20 years at a 6% discount rate โ with a clear payback point.
Read the worked example โAn 80 m freeze-protection circuit on a 114 mm insulated pipe sizes cleanly for heater output and breaker rating โ but adding the heating cable's own resistance reveals a voltage drop that blows past any reasonable limit.
Read the worked example โA standard free-standing MCC enclosure with 600 W of internal losses โ checked against its own natural-convection dissipating capacity, which turns out to fall well short, forcing a forced-air fan sizing calculation.
Read the worked example โ