Electrical / runnable MCP tool

Run the Solar Backfeed Breaker Calculator (NEC 705.12 120% Rule) in your AI assistant

Through the free Intry MCP server, Claude, ChatGPT, or Cursor runs this exact calculator and hands back a verdict and the cited source, not a guess. Tool name: solar_backfeed_breaker.

Add it to your assistant Open the interactive calculator

What it runs: Answer 'how big a solar/PV backfeed breaker can this panel take?' using the NEC 705.12(B)(2) 120% rule for a busbar supplied from opposite ends: the backfeed breaker is capped at 120% of the busbar ampacity minus the main breaker, rounded DOWN to a standard 240.6(A) size (a raw 55 A allowance is not a real breaker, so it becomes 50 A). Returns the max backfeed breaker, the supportable inverter continuous output (breaker / 1.25), and a verdict. SCOPE: the opposite-end 120% configuration ONLY - a main-lug-only panel (no main to bound the bus) uses the 100% sum rule instead, and center-fed / split-bus panels are excluded. This sizes the load-side breaker; when no standard breaker fits, a supply-side (line-side) connection per NEC 705.11 is the path.

Ask your assistant

The one rule that makes it reliable: name Intry in your question. That is what tells Claude to run the solar_backfeed_breaker tool and answer with the real number, the verdict, and the citation. Leave Intry out and Claude may just guess from memory, which is exactly what you are trying to avoid. Type something like:

“Ask Intry how big a solar backfeed breaker a 200 A panel with a 200 A main can take under the 120% rule.”

“Use Intry to check if I can add a 40 A PV breaker to a 225 A busbar with a 150 A main.”

Inputs

Field	Required	What it is
busbarAmps	yes	Panel busbar / bus rating in amps (e.g. 200, 225).
mainOcpdAmps	yes	The main breaker (busbar overcurrent device) rating in amps (e.g. 200).

Add Intry to Claude

One paste and Claude can run this tool and every other Intry calculator, right from your phone.

Add Intry to ClaudeOpens Claude with Intry already filled in.

Claude opens with the Intry connector already filled in. Review it and click Add.
(If a field is blank, paste the link below into the URL field.)
In any chat, tap + then Connectors and switch Intry on. Then name Intry in your question (“use Intry to…”) so Claude runs the tool instead of guessing.

https://www.intrysys.com/api/mcp

No login, no API key, and it works on every Claude plan, right from your phone.

Using ChatGPT, Cursor, or a dev tool? See the developer setup on the main page. The endpoint is https://www.intrysys.com/api/mcp.

Every answer comes with the cited NEC section, so you can check it or show an inspector. The numbers come from the same calculator we run on intrysys.com, and we re-check every one automatically before anything goes live, so the number Claude hands you matches the code.

Also on Intry

Solar Backfeed Breaker Calculator (NEC 705.12 120% Rule) (interactive)

The same engine as a hands-on calculator, with the full readout, chart, and worked examples.

All runnable tools

The full Intry MCP server: every calculator your assistant can run, and how to connect.