Electrical / runnable MCP tool
Run the Box Fill Calculator 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: box_fill.
What you get back: total volume used vs the box volume, pass/fail, and a suggested box if over.
How it computes the answer
Computed from NEC Table 314.16(B)(1) per-conductor volumes and the 314.16(B)(1)-(6) counting rules, against the Table 314.16(A) box volume.
What it cites
Your assistant gets the same verdict and the same citation a technician gets on the interactive calculator, because both call one engine. These are the sources that engine reads.
- NEC Table 314.16(B)(1)
- Free space required within a box, per conductor, by AWG: #18 = 1.50, #16 = 1.75, #14 = 2.00, #12 = 2.25, #10 = 2.50, #8 = 3.00, #6 = 5.00 cu in. Taken from the NEC 2023 book itself, page 70-196, and transcribed twice by two different methods so that a misread column could not survive both. The two readings disagreed on which allowance belongs to which wire size, and the disagreement is the reason both were done: the values this tool uses are the ones the printed page actually shows.
- NEC 314.16(B)(1) through (B)(6)
- The counting rules: each conductor (B)(1); one allowance for all cable clamps (B)(2); one for one or more support fittings (B)(3); two for each device yoke (B)(4); one for all equipment grounding conductors sized on the largest EGC, plus a quarter-volume for each grounding conductor beyond four (B)(5); and one for each terminal block (B)(6), new in the 2023 NEC. Each conductor-based allowance uses the largest conductor of that kind.
- NEC Table 314.16(A)
- The listed volume of each standard box type, used when you pick a box instead of entering a custom cubic-inch volume. Fetched from the primary.
These are NEC Article 314 table values, summed by the engine for the conductors, devices, and fittings you enter, not measurements. The result is the code fill; the installer confirms the actual box and its listed volume on site.
The full receipt, with every source and how each is cross-checked, is on the interactive Box Fill Calculator.
Ask your assistant
The one rule that makes it reliable: name Intry in your question. That is what tells Claude to run the box_fill 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:
Inputs
| Field | Required | Accepts | What it is |
|---|---|---|---|
| boxType | optional | string | Standard box type key (e.g. '4x1-1/2 square'), or omit and pass customVolume. |
| customVolume | optional | number | Box volume in cubic inches (overrides boxType). |
| conductors | yes | array of { size: 18 | 16 | 14 | 12 | 10 | 8 | 6; count: number } | Insulated conductors entering the box. |
| deviceYokes | optional | number | Number of devices (switch/receptacle yokes). Default 0. |
| largestDeviceConductor | optional | 18, 16, 14, 12, 10, 8, 6 | Largest conductor on a device. Default largest present. |
| internalClamps | optional | boolean | Internal cable clamps present? Default false. |
| largestClampConductor | optional | 18, 16, 14, 12, 10, 8, 6 | Largest conductor for the clamp allowance. |
| egcCount | optional | number | Number of equipment grounds. Default 0. |
| largestEgc | optional | 18, 16, 14, 12, 10, 8, 6 | Largest EGC size. |
| terminalBlocks | optional | number | Number of internal terminal blocks. Default 0. |
| luminaireStud | optional | boolean | Fixture stud present? Default false. |
| hickey | optional | boolean | Hickey present? Default false. |
Add Intry to Claude
One paste and Claude can run this tool and every other Intry calculator, right from your phone.
- 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/mcpNo 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.