Resources
Free tools. No login. No upsell.
The same NEC-compliant calculators we built for our platform, available to everyone, no account required. Use them on the next job. No watermarks, no rate limits, no “upgrade for full results” nonsense.
Free Solar Diagram Editor
Draw a real single-line diagram in your browser: actual equipment, wires that size themselves, live NEC checks. No account needed to start.
PV Interconnection Method Selector
Match your service style and inverter to the interconnection methods that fit, with the real wiring diagram and edition-aware NEC code basis.
Conduit Sizing Calculator
Determine proper conduit size based on NEC fill requirements.
Load Calculator
Residential service load calculations to NEC Article 220.
Voltage Drop Calculator
Wire sizing and voltage drop across distance, AC and DC.
Fault Current Calculator
Available fault current at the end of a conductor run.
Row Spacing Calculator
Solar panel inter-row spacing to avoid winter-solstice shading. Latitude, tilt, azimuth.
Guides
Reference articles for the rules behind the tools.
The NEC sections, design conventions, and inspection checks that drive what the calculators output. Bookmark for the next plan check or AHJ conversation.
NEC Compliance
The 120% Rule vs Power Control Systems
What the solar 120% rule (NEC 705.12) is, how an NEC 705.13 Power Control System differs, when a PCS lets you skip a service upgrade, and where the 120% rule still applies.
NEC Compliance
The Solar 120% Rule (NEC 705.12), Done Right
The 120% busbar rule with the correct citation for every code cycle (2017, 2020, 2023), worked examples, the MLO exception, subpanel propagation, and every fix when a design fails it.
NEC Compliance
PV String Sizing, Explained Properly
The full variable checklist behind NEC 690.7: eight panel inputs, six inverter constraints, ASHRAE temperature corrections, per-MPPT current limits, and the step-by-step math.
NEC Compliance
Service Disconnect Locations
The two-layer problem: NEC 230 and 705 are the floor, but the utility interconnection rules are where a code-perfect planset still gets rejected. Both layers, with the common rejection causes called out.
Solar Design
Solar Wiring Diagram Guide
What every PV (and PV + storage) wiring diagram needs: single-line vs three-line, conductor schedule, OCPD, EGC, AC disconnects, and the labels every AHJ checks.
Solar Design
Solar Panel Row Spacing
How inter-row spacing is computed at the worst-case sun angle of the year, with a live 3D viewer that rotates as you change azimuth and tilt.
Beyond the calculators
These tools are part of a bigger platform.
The same calculations run live as you design plansets in Solar Design Lab. Your team does the design. The platform does the engineering. $50 per planset, flat. Revisions included.