Engineering Calculators for Power & Energy Systems

Using the K-factor method: VD = (2 × K × I × D) / CM for single-phase or VD = (1.732 × K × I × D) / CM for three-phase, where K is a resistivity constant (about 12.9 for copper, 21.2 for aluminum), I is load current in amps, D is one-way distance in feet, and CM is the conductor's circular mil area. This is an approximation that ignores reactance and is best suited to feeders under about 250 feet.

Divide your real load in kW by its power factor to get required kVA, then round up to the nearest standard transformer nameplate rating (common ANSI/IEEE sizes include 75, 112.5, 150, 225, 300, 500, 750, and 1000 kVA). Always leave margin for future load growth.

Multiply the critical load in kW by the required backup duration in hours to get usable energy in kWh, then divide by your assumed depth of discharge and round-trip efficiency (commonly around 90% each for LFP systems) to get the nameplate energy rating you need to procure.

No. These tools use standard simplified formulas for early-stage budgetary sizing and procurement planning. Final designs, especially fault current and arc-flash coordination, require a licensed engineer's study using actual system impedances.

The theoretical Lee equation (NFPA 70E Annex D, for open-air arcs above 600V) and the empirical Doughty equations (for open-air or in-a-box arcs at 600V or below) estimate incident energy in cal/cm² from the bolted fault current, system voltage, arc duration, and working distance. These are simplified, standard-referenced methods for early-stage estimates — a real arc-flash study for PPE selection and labeling should use the full IEEE 1584 arcing-current method performed by a qualified person.

Divide the fuel tank capacity (gallons) by the fuel consumption rate at your expected load (gallons per hour), taken from the generator's own spec sheet — most gensets publish consumption rates at 50%, 75%, and 100% load.