Power System Calculators

Solve V = IR and P = VI for any combination. Returns active, reactive, and apparent power for AC loads with a power factor input. The foundation under every other calculator on this page.

NEC 310 ampacity sizing, voltage drop check, and NEC Chapter 9 conduit fill. Picks the larger of ampacity-required vs voltage-drop-required size and reports both.

Stub-up, offset, saddle, and back-to-back 90 bend marks for EMT, PVC, RMC, and IMC. Cosecant-based offset multipliers cover any angle, not just 30°.

Sizing from load (kW + power factor + safety margin), kVA-to-current conversion, fault current from %Z, and buck-and-boost guidance. Single- and three-phase formulas built in.

kW, kVA, kVAR; full-load current of motors, transformers, and resistive heaters; and three-phase voltage imbalance per NEMA MG-1. Single tab for power, one for FLA, one for imbalance.

kVAR sizing to lift PF from current to target. Returns capacitor µF for both wye and delta connections, line current draw, and an estimate of monthly demand-charge savings.

Standby and prime generator sizing: kW or kVA to full-load amps, plus fault-current contribution from a generator running on its own subtransient reactance. Sizing rules-of-thumb table for healthcare, data centers, and industrial.

Series and parallel resistance, complex impedance (R + jX), series/parallel impedance combinations, and the AC power triangle. Worked examples and the parallel-resistor formula explained inline.

IEEE 1584-2018 incident energy at the working distance, NFPA 70E PPE category determination, and arc flash boundary. Screening tool — a real arc flash study still requires a one-line and short-circuit data.

Substation ground grid resistance per IEEE 80, plus touch and step potential checks against the IEEE 80 safety thresholds. Output drives whether the grid passes or needs additional rods/conductors.

Motor full-load current per NEC 430.250, branch-circuit conductor and OCPD sizing per NEC 430.52, plus speed/torque/efficiency conversions. Standard NEMA design type and starter-method options included.

OCPD sizing per NEC 240, time-current coordination across two and three devices, and basic 50/51 relay setting calculations. Good for sanity-checking what came back from a coordination study.

Stationary battery sizing for substation DC systems, UPS, and SCADA backup: amp-hour capacity, cell count, string configuration, and autonomy time per IEEE 485.

Total residential load per NEC 220, service-conductor and OCPD sizing, ground electrode conductor per NEC 250, and grounded-conductor calc. The fast tool for a 100, 150, or 200 amp service entrance.

Utility-scale and commercial renewable: PV array sizing per NEC 690, battery storage capacity with depth-of-discharge, and load-profile analysis. Built around interconnection studies, not residential rooftop solar.

Quick FLA lookup for motors (HP and kW), transformers (kVA), and resistive heaters across single- and three-phase. Use this when you only need the number, not the full motor or transformer calculator.

NEC 210.19 voltage drop check for single- and three-phase circuits, copper or aluminum, with reactance. Routes to the Wire & Cable calculator (where it lives as a tab).

NEC Chapter 9 Table 1 fill check (53/31/40% rules) across EMT, PVC, RMC, and IMC. Routes to the Wire & Cable calculator (where it lives as a tab).

Available fault current at the transformer secondary and at any downstream device location. Drives NEC 110.9 interrupting rating selection on every breaker and fuse.

Step-by-step sizing for commercial standby and prime generators: running load, largest motor starting kVA, redundancy, plus NEC 517/700 and NFPA 110 code adders.