NEC Electrical Calculators

Electrical calculators built for the field, not the classroom

SparkyTools is an electrical calculator app for electricians who need fast, NEC-referenced answers on a phone. Conduit fill, voltage drop, motor FLA, fault current, transformer and panel load — each calculator is tuned for jobsite speed so you can keep moving instead of flipping through tables.

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What's inside the calculator set

Every calculator references the relevant NEC 2023 tables and gives you a clear result you can act on.

Conduit Fill

Size conduit using NEC Chapter 9 Tables 5 and 5A. Enter conductor type, size and count to check fill percentage and avoid derating surprises.

Voltage Drop

Estimate voltage drop over a run length so your farthest loads stay within acceptable limits. Works for common copper and aluminum conductor sizes.

Motor FLA & Sizing

Look up full-load amperes for three-phase and single-phase motors and size overcurrent protection and conductors with NEC 2023 references.

Fault Current

Calculate available fault current at a point in the system to verify interrupting ratings and equipment selection.

Transformer Sizing

Size transformers and primary/secondary protection for the load you actually serve.

Panel Load & Demand

Apply NEC demand factors to estimate service and feeder loads instead of adding every circuit at 100%.

Who uses these calculators

  • Apprentices checking conduit fill and voltage drop on a classroom takeoff before it hits the field.
  • Journeymen pulling feeder runs and verifying motor FLA against the nameplate during a service call.
  • Foremen sizing temporary power and fault-current ratings for a new jobsite distribution setup.
  • Contractors putting together a quick panel load estimate before sending a proposal.

A practical field example

You're on a commercial retrofit pulling a 250-foot feeder to a new sub-panel. Open the voltage drop calculator, enter the length, conductor size and load, and confirm the drop is within limits before you order wire. Then jump to the conduit fill calculator to verify the conduit size for the number of current-carrying conductors in the raceway. Two calculations, one app, no printed tables — and you can screenshot the result for your records.

Run your first calculation in under a minute

The free plan includes core NEC calculators. Pro unlocks higher-volume daily reports and AI. No credit card to start.