WireGaugeCalc Free calculator · NEC cited · works offline
Sizing Transfomer Secondary Conductor Calculator
Sizing transfomer secondary conductor calculator work is fast with WireGaugeCalc, since you enter the secondary current and the tool returns a wire size.
It reads the secondary amps, the conductor material, and the termination column, so the AWG follows NEC 310.16 ampacity.
You get a secondary conductor size before you set the transformer.
Open the calculatorEnter any two values and read the rest.
Ohm’s law: V = I × R and P = V × I. Field aid only, verify against the current NEC and your local authority having jurisdiction.
From secondary current to a conductor size
Secondary current rises as the kVA grows, so a larger transformer drives a larger conductor.
WireGaugeCalc takes your secondary amps and matches them to the 310.16 ampacity table.
The conductor must carry the full secondary current, so the size follows that load.
What the secondary conductor size depends on
A few values set the secondary conductor size:
- Secondary current in amps from the transformer
- Conductor material, copper or aluminum
- Termination temperature column at the equipment
- The matching NEC 310.16 ampacity
- The next standard AWG when the current falls between sizes
One app for every NEC calculation
WireGaugeCalc keeps the calculations you reach for most in one place:
- Voltage drop and wire sizing for any run
- Conduit fill for EMT, PVC, and RMC
- Box fill and junction box sizing
- Ampacity and temperature derating
- Motor circuit and load calculations
- Conduit bend offsets and saddles
Built for the field, works offline
The whole app runs on your phone, so it keeps working in a basement, an attic, or a job site with no signal.
There is no account to create and nothing to load. Open it, run the number, and get back to work.
- No signup and no signal needed
- Answers in a tap, not a spreadsheet
- Same tool on phone, tablet, and desktop
Every result cites the NEC article
Each answer shows the table or formula it came from, so you can check the method and learn the code as you go.
That makes the app useful on the job and during exam prep, since the reasoning is right next to the number.
Switch the code year your job runs on
Jurisdictions adopt the NEC at different times, so you can match the calculation to the code in force:
- NEC 2017, 2020, and 2023 tables
- Copper and aluminum conductors
- 60, 75, and 90 degree C terminations
- Single-phase and three-phase systems
Run the number, then get back to work
Stop flipping through a paper book or hopping between calculator sites. Enter your values, read the code-cited answer, and move on. Free to use, no signup.
Open the calculatorFrequently asked questions
How do I find the secondary current?
Divide the transformer kVA by the secondary voltage, then adjust for phase. The calculator sizes the conductor once you enter that current.
Does the secondary conductor have its own overcurrent rules?
Yes, transformer secondary conductors follow specific NEC tap and protection rules. Confirm the conductor size and protection against the current NEC and your local authority having jurisdiction.
Is WireGaugeCalc free to use?
Yes. Every calculator is free to run with no signup. A paid tier adds saved projects, PDF reports, and extra code years, but the core math stays free.
Does it work without internet?
Yes. The app runs on your device, so it keeps working with no signal on a job site, in a basement, or in an attic.
Are the results code accurate?
Results follow published NEC tables and standard formulas, and each answer shows the article it came from. It is a field aid, not a stamp of approval, so verify against the current code and your local authority before you wire anything.
Which NEC code year does it use?
You can switch between NEC 2017, 2020, and 2023, since jurisdictions adopt the code at different times. Pick the year your job runs on.