Calculators
Every result shows its inputs, steps, NEC references, assumptions and warnings.
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Conductors & Raceways
Ampacity, derating, fill and box sizing
Voltage Drop
Voltage drop and percentage for a run, by NEC Chapter 9, Table 9 or the resistivity approximation.
Conductor Ampacity & Derating
Looks up base ampacity, then applies ambient temperature correction and adjustment for bundled conductors.
Medium Voltage Cable Ampacity
Looks up Type MV cable ampacity from NEC 315.60(C) by installation, then applies ambient correction.
Wire Ampacity Reference
Table 310.16/310.17 base ampacity by size, material and installation method.
Copper vs. Aluminum
Sizes a circuit in both materials (0–2000 V, Table 310.16/310.17/310.20) and compares the ampacity, size and rough cost delta. Supports parallel sets for loads above a single conductor's ampacity.
Conduit Fill
Checks conductors against the permitted fill for a chosen conduit type and trade size.
Raceway Sizing
Finds the smallest trade size of a conduit type that accepts a set of conductors.
Box Fill
Required box volume for the conductors, clamps, fittings, devices and grounds in an outlet or device box.
Pull & Junction Box Sizing
Minimum box dimension for a straight, angle or U pull, for conductors 4 AWG and larger.
Load Calculations
Service, feeder and branch-circuit loads
Continuous Load (125%)
Minimum conductor and overcurrent-device rating for a load with a continuous portion.
Dwelling Service Load
Standard-method service load for a dwelling, from floor area, appliances, range, dryer and space conditioning.
Optional Dwelling Load
Optional service load for a dwelling under 220.82, often smaller than the standard method.
Feeder & Branch-Circuit Load
Minimum conductor ampacity and device rating from continuous, non-continuous and motor loads.
Generator Sizing
Total connected load against a generator's rating, with a motor starting-surge check.
Panel Schedule Builder
Lays circuits into a panel and tallies spaces used, per-leg current and balance.
Energy Cost Estimator
Appliance wattage and daily runtime, priced at your electricity rate.
Load Current & Power
Convert between current, apparent power and real power for DC, single-phase and three-phase loads.
Protection & Grounding
Overcurrent devices and grounding conductors
Standard Overcurrent Device
Nearest standard fuse or breaker ratings above and below a required current, with the next-size-up conditions.
Equipment Grounding Conductor
Minimum equipment grounding conductor for an overcurrent device rating, including proportional upsizing.
Grounding Electrode Conductor
Grounding electrode conductor for a service, from the service-entrance conductor size.
Transformer Overcurrent Protection
Maximum primary and secondary protection for a transformer, by protection method — Table 450.3(B) at 1000 V and below, Table 450.3(A) above it.
Motors & Equipment
Motors, transformers, HVAC and EV supply
HVAC Circuit Ampacity & Protection
Minimum circuit ampacity and maximum overcurrent protection for air conditioning and refrigeration equipment.
EV Supply Equipment Circuit
Continuous-duty ampacity, breaker and conductor size for an EV charging circuit.
Motor Branch Circuit
Conductor ampacity, short-circuit protection and overload for a single motor, from the full-load current tables — including the DC rectifier, multispeed, wye-delta, part-winding and duty-cycle cases.
Multiple-Motor Feeder
Conductor ampacity for several motors plus other loads, at 125 percent of the largest motor and continuous load, plus the rest.
Group Motor Branch-Circuit Protection
Short-circuit and ground-fault protection for two or more motors, or motors and other loads, on one branch circuit — Cases A, B or C.
HP, Amps & Power Converter
Converts between horsepower, current, apparent power and real power.
Transformer Current
Full-load current on the primary and secondary windings from the kVA rating and winding voltages.
Solar PV
Array voltage, current and conductor sizing
PV Maximum System Voltage
Coldest-day array voltage from module open-circuit voltage, by temperature coefficient or Table 690.7(A).
PV Maximum Circuit Current
Maximum current for a PV source, dc-to-dc converter or inverter output circuit, before conductor sizing.
PV Conductor Sizing
Smallest PV circuit conductor satisfying both 690.8(B) tests, with the governing one named.
PV String Sizing
Permitted range of modules in series against an inverter's voltage window, at both temperature extremes.
PV Overcurrent Device
Overcurrent device rating for a PV circuit, checked against the module's maximum series fuse rating.
Inverter Output Circuit
Maximum current, required conductor ampacity and overcurrent device for an inverter output circuit.
Load-Side Interconnection
Checks a back-fed PV connection against the busbar under every arithmetic method in 705.12(B).
Feeder Tap Interconnection
Checks a power source connection to a feeder against every applicable test in 705.12(A).
Supply-Side Interconnection
Conductor size for a connection ahead of the service disconnect, against both the ampacity and the 705.11 floor.
PV Equipment Grounding Conductor
Grounding conductor for a PV circuit, including the assumed device where the circuit has no overcurrent protection.
Rapid Shutdown Checklist
Whether 690.12 applies, and the voltage and time limits the installation must meet if it does.
Required PV Labels
The marking a PV installation must carry, from how the system is built and interconnected.
Battery Backup Runtime
Estimated backup hours from a connected-load list and usable battery capacity.