Electrical / runnable MCP tool
Run the Wire Size 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: wire_size.
What you get back: wire size, breaker, ground, and a verdict.
How it computes the answer
Sized from NEC Table 310.16 at 125% for a continuous load (210.19(A) conductor / 210.20(A) device), with the 110.14(C) terminal cap (60°C on 100 A or less unless the equipment is marked for 75°C), the 240.6(A) breaker rule with 240.4(B) and (D), and the Table 250.122 ground, increased per 250.122(B) where the conductor is upsized.
What it cites
Your assistant calls the same engine the interactive calculator calls, with the inputs listed under Inputs. These are the sources that engine reads.
- NEC Table 310.16
- Allowable conductor ampacity by size, material, and insulation temperature column. NFPA 70-2023, p. 70-187. Cross-checked against the Helukabel and Cerrowire published ampacity tables. This is the general ampacity table for conductors in raceway or cable.
- NEC 210.19(A) and 210.20(A)
- Continuous-load sizing. A load running three hours or more is sized at 125%: both the conductor (210.19(A), whose (1) compares that 125% figure with the ampacity before any correction or adjustment factor and whose (2) compares the load with the ampacity after them) and the overcurrent device (210.20(A)). The web calculator treats the load as continuous by default, so the 125% factor is applied unless you turn it off; the wire size tool an AI assistant calls over MCP treats a load as NOT continuous (sized at 100%) unless the assistant says the load is continuous, so for a load running three hours or more it must say so, and its readout names which basis it used.
- NEC 110.14(C)
- Terminal temperature limitation. Ampacity is held to the lowest temperature rating of any connected termination, even when a 90°C conductor is installed. On a circuit rated 100 amperes or less, 110.14(C)(1)(a) makes the 60°C column the rule and allows the 75°C column only under (3), "Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors" (NFPA 70-2023, p. 70-65); over 100 amperes, 110.14(C)(1)(b) makes 75°C the baseline. NEC 334.80 holds NM-B cable to the 60°C column. The calculator sizes on the column you choose, and where the 75°C answer holds only on equipment marked for it, it says so and gives the 60°C conductor from the same engine. This is the cap most calculators skip.
- NEC 310.15(B)(1) with Table 310.15(B)(1)(1), and Table 310.15(C)(1)
- Ambient-temperature correction factors (310.15(B)(1)) and the more-than-three-conductor bundling adjustment (310.15(C)(1)), applied to the base ampacity before the terminal cap.
- NEC 240.6(A) and 240.4(B)
- Standard overcurrent-device ratings (240.6(A)). The breaker is the smallest standard OCPD that both protects the conductor and covers the design load; where the ampacity does not land on a standard rating, 240.4(B) permits the next standard size up (800 A and under) only on a circuit that is not a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads, and every answer that relies on it says so and names the conductor that circuit would need. Fetched two-pass from the primary.
- NEC 240.4(D)
- Small-conductor overcurrent cap: #14, #12, and #10 copper are limited to 15, 20, and 30 A regardless of their table ampacity (aluminum #12 and #10 cap at 15 and 25 A). Verified against both the 2017 and 2023 editions.
- NEC Table 250.122
- Equipment grounding conductor, sized from the circuit's overcurrent device. NFPA 70-2023, p. 70-158, copper and aluminum columns. Where the sized conductor is larger than the smallest the code permits for this load (210.19(A)(1)'s two tests, either 310.15(B)(1) method), 250.122(B) increases the ground in proportion to the circular mils, computed by the same engine as the ground wire size chart, and the answer says 250.122(B) beside it.
These are NEC table values, looked up and applied by the engine under the conditions you enter, not laboratory measurements. The calculator does the 125% continuous sizing, the derating, and the 110.14(C) terminal cap for you; the installer is responsible for the final conductor choice and the conditions of use.
The full receipt, with every source and how each is cross-checked, is on the interactive Wire Size Calculator.
Ask your assistant
The one rule that makes it reliable: name Intry in your question. That is what tells Claude to run the wire_size 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 |
|---|---|---|---|
| amps | yes | number | Load current in amps. |
| continuous | optional | boolean | Continuous load (3h+)? Applies the 125% factor. Default false. |
| voltage | optional | number | System voltage (default 240). |
| phase | optional | single, three | Default single. |
| material | optional | cu, al | Default cu. |
| insulation | optional | TW, UF, THW, THWN, XHHW, RHW, USE, THHN, THWN-2, XHHW-2, RHH, RHW-2, USE-2 | Insulation type (THHN, THWN-2, XHHW-2, TW, THW, ...). Default THHN. |
| ambientTemp | optional | number | Ambient temperature in °F (default 86). |
| conductorsInConduit | optional | 1-3, 4-6, 7-9, 10-20, 21-30, 31-40, 41+ | Current-carrying conductors in the raceway (default '3'). |
| distance | optional | number | One-way run length in feet (informational; default 0). |
| terminationC | optional | 60, 75 | Equipment termination temperature rating per NEC 110.14(C)(1), from the marking on the breaker, panelboard and lugs. 60 for unmarked or 60°C-marked equipment, 75 for 60/75°C or 75°C-marked. Default 75. NEC 110.14(C)(1)(a) makes 60°C the column for circuits rated 100 amperes or less UNLESS the equipment is listed and marked otherwise, so 75 is a marking-conditional value and not the code default. If the marking is unknown, 60 is the conservative choice. |
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.