WireGaugeCalc Free calculator · NEC cited · works offline
25 Kva Secondary Wire Sizing
25 kva secondary wire sizing is simple with WireGaugeCalc, since it finds the secondary current and a conductor gauge from the transformer rating.
You enter the kVA, the secondary voltage, and the phase, so the tool computes amps and reads NEC 310.16 ampacity.
The result gives you a conductor that carries the secondary load at your termination temperature.
Open the calculatorSmallest conductor whose ampacity meets the load, NEC Table 310.16. Field aid only, verify against the current NEC and your local authority having jurisdiction.
Getting Secondary Current For 25 Kva Wire Sizing
Conductor size starts from current, so 25 kva wire sizing first converts the rating to secondary amps using voltage and phase.
On a 208V three-phase secondary, 25 kVA works out to about 69 amps, since you divide volt-amps by voltage and the square root of three.
The tool then picks a gauge from NEC 310.16 at your chosen termination column.
Inputs For Sizing The Secondary Conductors
These values set the secondary conductor gauge:
- Transformer kVA rating, here 25 kVA
- Secondary voltage, such as 208V or 240V
- Single-phase or three-phase configuration
- Conductor material, copper or aluminum
- Termination temperature column from NEC 310.16
- Secondary overcurrent protection per the transformer article
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 amps for a 25 kVA transformer?
Divide the volt-amps by the secondary voltage, and for three-phase also divide by the square root of three. A 25 kVA unit at 208V three-phase yields roughly 69 amps.
Does the secondary conductor follow the transformer protection?
Secondary conductor sizing ties to the transformer overcurrent rules in the transformer article, not just the load current. Verify the protection and conductor size against the current NEC and your local authority having jurisdiction.
Can I use aluminum for the secondary conductors?
Yes, but aluminum carries less per size than copper, so the gauge goes up. Read the ampacity from the correct termination column before you finalize the size.
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.