Engineering calculators, built in the open
The dwelling load engine is live for electrical designers today. The tools below are planned next; tell us which one you need first.
Available now
Contractor Load Calculator
ProDwelling-unit service and feeder load per NEC 2023 Article 220, standard and optional methods, exported as a permit-ready packet with cover sheet and panel schedule.
Calculated per NEC 2023
Start a free trial →Panel Schedule Builder
ProTurn a saved load calculation into a balanced 120/240 V panel schedule: circuits per load, leg balancing, spares, tandems, and a schedule section in the permit packet.
Calculated per NEC 2023
Start a free trial →Common questions
The load-calculation questions electricians ask, each worked through the same engine engineers use.
- Load calculationsWhat does a 200 A service load calculation look like, line by line?A complete NEC 2023 Article 220 standard-method calculation for a 2,400 ft² all-electric house with a heat pump and well pump, every line item with its clause, plus the 220.82 optional method on the same house.
- EV chargingHow much does an EV charger add to a load calculation, by charger amps?Standard-method results for one 2,000 ft² house with a 16, 24, 32, 40, 48 and 80 A EV charger under NEC 2023 (220.57 floor plus the 125% continuous adder) and NEC 2026 (120.57 nameplate, no adder).
- PanelsAre tandem breakers allowed, and how many can a panel take?Yes, where the panelboard is listed for them. What the CTL limit and the "30/40" on a panel label mean, and a panel schedule engine placing 36 circuits in a 30-space, 40-circuit panel versus a 30/30 panel.
Planned
Built on the same clause-by-clause approach as the load calculator. Order is decided by the interest below.
Voltage Drop Calculator
PlannedConductor voltage drop for single- and three-phase feeders and branch circuits, copper and aluminum, with NEC 210.19 and 215.2 informational-note limits.
Fault Current Calculator
PlannedAvailable fault current at the service and downstream panels from utility contribution, transformer impedance and conductor runs, for AIC selection.
Three-Phase Load Calculator
PlannedBalanced and unbalanced three-phase feeder and service loads with per-phase amps and neutral current.
Transformer Sizing Calculator
PlannedkVA selection from connected and demand load with growth allowance, primary and secondary OCPD per 450.3.