Offline
No internet, no account required.
NEC 690
Validated against the standard.
PDF export
Pro-only. Generate professional reports.
$2.99 Pro
Lifetime unlock. No subscriptions.
How it works
Enter your values
Type in your inputs — the app fills code tables and constants for you, so there's nothing to look up.
Get a code-checked result
Instant answer with a clear PASS / FAIL and the exact NEC 690 reference behind every number.
Save & export
Keep a history of calculations and export a clean PDF report to share or attach to a permit (Pro).
What this calculator does
Long PV runs from a roof array to the inverter and from the inverter to the panel can lose meaningful energy to voltage drop. This app sizes PV DC and AC conductors to hit a tight drop target — usually 2% or less on the DC side — so you keep the energy you paid for.
How it works
- Enter string or circuit current, one-way distance, and conductor size.
- The app computes drop from the conductor resistance and compares it to your target.
- It handles both the DC string/home-run and the AC output circuit.
Worked example
A 10 A string over a 120-foot DC home run on #10 copper drops roughly 2.9 V. On a 380 V string that is under 1%, but on a low-voltage microinverter trunk the same run could exceed 2% and call for larger wire.
Related calculators
Size the conductors with the solar wire sizing calculator and the raceway with the solar conduit fill calculator.
Solar voltage drop FAQ
What drop target should PV use?
PV designers commonly hold DC circuits to 2% or less, tighter than the general 3% recommendation, because the loss runs all day, every day, over the system's life.
DC and AC circuits?
Both. The app handles the DC string and home-run as well as the inverter AC output circuit, each with its own current and voltage.
Copper and aluminum?
Yes, with the correct resistance for each, since aluminum needs a larger size to match the drop of copper.
Does it work offline?
Yes, it runs 100% offline with no account. Free with rewarded ads; a one-time $2.99 Pro unlock adds PDF export and saved history.
Get Voltage Drop Solar on your phone
Free with rewarded ads · $2.99 lifetime Pro · iOS & Android. Works 100% offline on the job site.