Electrical & NEC
32 free electrical & nec tools in the Calculators & Converters collection — every one runs in your browser with no signup and no uploads.
Box Fill Calculator (NEC 314.16)
Sum conductor, device, clamp, and fitting equivalents to verify junction/outlet box fill
Bundling (Adjustment Factor) Derating Calculator (NEC 310.15(C))
Apply NEC bundling adjustment factors when more than 3 current-carrying conductors share a raceway
Busbar Ampacity Calculator
Estimate the current-carrying capacity of copper or aluminum bus bars.
Cable Tray Fill Calculator (NEC 392)
Verify cable tray fill area for single and multiconductor cables per NEC Article 392.
Ground Fault Loop Impedance Calculator
Verify that fault current through the EGC is enough to trip the breaker in time.
Harmonic Derating (K-Factor) Calculator
Calculate transformer K-factor from a harmonic current spectrum to select a K-rated transformer
Lighting Power Density (LPD) Calculator
Calculate installed lighting power density in W/ft² and compare against ASHRAE 90.1 limits.
LiPo C-Rating & Max Burst Current Calculator
Find safe continuous and burst current limits for any LiPo pack
Microgrid Load Shedding Priority Calculator
Assign load-shedding priority tiers to circuits and find generator or battery runtime per tier.
Motor Starting (LRA) Current Calculator
Estimate locked-rotor amperes and starting kVA for AC induction motors by NEMA code letter.
NEC Tap Rule Calculator (210% and 100 A Rules)
Check NEC 240.21 tap rules for 10-ft, 25-ft, and outside feeder taps
Multifamily Dwelling Load Calculation (NEC 220.84)
Size service for apartment buildings using NEC 220.84 optional demand factors
NEC 310.16 Full Ampacity Table Lookup
Searchable NEC 310.16 conductor ampacity table for copper and aluminum at 60/75/90 °C
NEC Article 430 Motor Circuit Summary Calculator
Get FLC, conductor, max OCPD, overload, and disconnect for a motor in one step.
NEC Demand Factor Calculator
Apply NEC Article 220 demand factors to reduce calculated load for services and feeders.
NEC GFCI/AFCI Requirement Checker
Look up 2023 NEC GFCI and AFCI protection requirements by room type and circuit voltage
NEC Kitchen Circuit Requirements Calculator
List the dedicated kitchen circuits required per NEC 210.52, 210.8, and 210.12
Panel Schedule / Load Center Calculator
Build a load center panel schedule, auto-assign circuits to legs, and compute total demand.
NEC Chapter 9 Table 9 AC Resistance & Reactance Lookup
Look up AC resistance and reactance per 1000 ft by conductor and conduit type
Phantom Power Cable Resistance Drop Calculator
Estimate phantom power voltage drop across XLR cable resistance
Total Harmonic Distortion (THD) Calculator
Calculate voltage or current THD from individual harmonic magnitudes
Receptacle Circuit Count Calculator
Calculate the minimum 20 A small-appliance and dedicated dwelling circuits required by NEC 210.11
Residential Optional Load Calculation (NEC 220.82)
Fast residential service sizing using the NEC 220.82 optional calculation method
Service Entrance Conductor Sizing Calculator
Size service entrance conductors from a calculated service load per NEC 230.42 and 310.12
Service Load Calculation (NEC 220)
Compute residential service load per NEC 220.82 optional dwelling-unit method
Short-Circuit Current Rating (SCCR) Calculator
Find available fault current at any point in a distribution system for SCCR and AIC verification
Single-Phase Panel Load Balancing Calculator
Balance circuit loads across panel legs to minimize neutral current and optimize panel capacity.
Surge Protective Device (SPD) Sizing Calculator
Select SPD type, MCOV, and discharge current for service-entrance and branch use.
VFD Motor Cable Derating & Shielded Cable Calculator
Conductor derating and shielded cable specs for variable-frequency drive installs
Wire Ampacity Calculator (NEC 310.16)
Look up conductor ampacity from the NEC 310.16 table by AWG/kcmil and insulation type
Parallel Resistance Calculator
Total resistance of resistors wired in parallel.
Series Resistance Calculator
Total resistance of resistors wired in series.