Electrical / runnable MCP tool
Run the Biggest EV Charger Calculator (NEC 220.87 + EVEMS) 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: max_ev_charger.
What you get back: the largest standard EVSE output that fits, plus the branch wire, breaker and ground. The added charger enters the 220.87 service check at 100% of its 220.57 value, so the fit is the service headroom divided by the voltage, floored to a standard rating; the 125% continuous factor sizes only its branch.
How it computes the answer
Computed from the NEC 220.87 inverse solve against your metered demand, with the EVEMS relaxing only the service calc (220.70 / 625.42(A) / 750.30); the branch is always 125% of the full charger output (210.20(A) / 625.41) on NEC Table 310.16 (75°C only on terminations marked for it, 110.14(C)(1)(a)(3)) with the 240.6(A) breaker and Table 250.122 ground.
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 220.87
- Existing-dwelling load method, run in reverse: your metered maximum demand at 125% sets the headroom, and the biggest charger is the amps left before the service rating is reached. The added charger enters the service check at 100% of its rating (its 220.57 value, no demand factor). NFPA 70-2023, p. 70-100.
- NEC 220.70
- Energy management systems, new in the 2023 NEC: an EMS-controlled maximum (the device setpoint) may be used as a single continuous value in the feeder and service load calculation. This is what lets a shed or throttle device relax the SERVICE calc without a panel upgrade.
- NEC 625.42 and 750.30
- EV charging is a continuous load (625.42). An external EMS relaxes only the service and feeder calculation (625.42(A) / 750.30), never the branch; the EVSE's own restricted-access adjusted setting under 625.42(B) is the one route the NEC gives for a smaller branch, and it is not one this tool takes: every condition 625.42(B) attaches, under 750.30(C) and the manufacturer's instructions, is a fact about installed equipment. The tools name the rule and size from the full rating.
- NEC 210.20(A) and 625.41
- The branch overcurrent device and conductor are sized at 125% of the FULL EVSE hardware output, always, for every external device type. An external shed or throttle does not change the EVSE's rating, so the branch is protected to what the unit can pull if the device fails or is bypassed.
- NEC Table 310.16
- Conductor ampacity for the branch, the general ampacity table for conductors in raceway or cable, read at the 75C column with the 110.14(C) terminal cap. The branch routes through the locked wire-size engine. Fetched from the primary (p.70-187).
- NEC 110.14(C)(1)(a)(3) and 334.80
- When the 75C column holds. On a circuit rated 100 amperes or less, 110.14(C)(1)(a) allows the 75C 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), and 334.80 holds NM-B cable to the 60C column. So where the branch this tool names holds only at 75C, the answer says so beside the conductor. Whether your breaker and charger are marked for 75C conductors is a fact on the equipment, not something this tool can see.
- NEC 240.6(A), 240.4(D), and Table 250.122
- Standard overcurrent-device ratings (240.6(A)), the small-conductor cap on #14/#12/#10 (240.4(D)), and the equipment grounding conductor sized from the overcurrent device (Table 250.122). Fetched from the primary (p.70-158).
- NEC 750.30(C)(1) through (C)(4), and 750.50
- The four conditions on using an EMS to limit current, stated by the code in the order the code states them. 750.30(C)(1) permits a single current setpoint equal to the system's maximum ampere setting, and names that same value as the one 220.70 allows in the connected-load calculation, which is why the two citations travel together in this tool. 750.30(C)(2) requires the system to use monitoring and controls that cease current flow automatically when the EMS malfunctions. 750.30(C)(3) permits adjustable settings only where access is behind a removable and sealable cover, behind a cover or door needing a tool, behind locked doors reachable only by qualified personnel, or under password protection. 750.30(C)(4) requires the equipment supplying the branch circuit, feeder or service to be field marked with the maximum current setting, the date of calculation and setting, the loads and sources tied to the current-limiting feature, and wording that the setting is not to be bypassed, marked per 110.21(B) and visible before servicing. 750.50 adds a directory of the controlled devices and circuits, posted on the controller, disconnect or branch-circuit overcurrent device. Not one of these is visible to a calculator, so this tool names them as site conditions and sizes the branch from the full charger output regardless. Read from the printed primary at folios 70-668 and 70-669 on 2026-08-23.
- NEC 220.60
- Noncoincident loads, NFPA 70-2023, p. 70-96: "If it is unlikely that two or more noncoincident loads will be in use simultaneously, using only the largest load(s) that will be used at one time for calculating the total load of a feeder or service shall be permitted." This is the section a circuit-share switch actually works under. It is why this tool's answer for that device type cites 220.60 and 220.57 and NOT 625.42(A), 220.70 or 750.30: time-sharing one existing branch invokes no service relaxation, and saying otherwise would attribute a branch-interlock answer to sections written about a service and a feeder.
- NEC 210.20(A)
- Branch-circuit overcurrent protection at 125 percent of a continuous load, p. 70-84. This is the rule behind the sentence this tool repeats on every path: the branch is always sized to the FULL charger output at 125 percent, whatever an energy management system does to the service calculation. 220.70 limits current to a feeder or service and never to a branch, which is the same split as 625.42(A) against (B).
- NEC 230.90 and NEC 240.4
- Named where this tool tells you a feeder or service still needs its own overcurrent protection. NFPA 70-2023, p. 70-115, 230.90(A): "Such protection shall be provided by an overcurrent device in series with each ungrounded service conductor that has a rating or setting not higher than the ampacity of the conductor." NEC 240.4 is the general conductor rule on the feeder side, p. 70-122 for the lead-in and (A), with 240.4(D) on p. 70-123. Neither is computed here; the tool names the requirement and stops.
- NEC 110.3(B)
- Equipment must be installed and used in accordance with its listing and labeling, which is why a manufacturer's instruction outranks a generic code minimum in this tool. It is the section behind the refusal that fires when a restricted-access adjusted rating is entered: NEC 625.42(B) permits an EVSE to be rated at that setting, but this tool accepts the value without applying it, says so in those words, and leaves the listed equipment's own instructions governing.
These are NEC 2023 demand rules and referenced tables, looked up and applied by the engine to the service and metered demand you enter, not field measurements. The service headroom is only as good as your metered peak. Any EVEMS must be listed and installed per its instructions; your AHJ and your actual metered demand have final say, and the branch is always sized to the full charger output.
The full receipt, with every source and how each is cross-checked, is on the interactive Biggest EV Charger Calculator.
Ask your assistant
The one rule that makes it reliable: name Intry in your question. That is what tells Claude to run the max_ev_charger 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 |
|---|---|---|---|
| serviceAmps | yes | number | Service / main breaker rating, e.g. 100, 125, 150, 200. |
| voltage | optional | number | Service/charger voltage (default 240; use 120 for Level 1). |
| demandSource | optional | utility, recording | Source of the peak-demand figure (default utility). |
| demandValue | yes | number | Existing measured peak demand. |
| demandUnit | optional | kw, a | Unit of demandValue (default a). |
| material | optional | cu, al | Branch conductor material (default cu). |
| distance | optional | number | One-way run length in feet (informational; default 0). |
| device | optional | shed, throttle, circuit-share | Load-management device TYPE. Omit for the plain 220.87 inverse solve. |
| deviceRatingAmps | optional | number | shed: the EVSE pass-through breaker; circuit-share: the existing shared-branch breaker; throttle: the EVSE hardware output. |
| hardwareOutputAmps | optional | number | The full EVSE hardware output the branch is protected to. Defaults from device+deviceRatingAmps if omitted. |
| evseAdjustedRatingAmps | optional | number | NEC 625.42(B): the EVSE's OWN restricted-access adjustable rating, if one is set. It is accepted but never applied to the branch: passing it does not shrink the conductor. It returns a blocker naming 625.42(B) / 750.30(C) and the site conditions that would have to be verified first. |
Add Intry to Claude
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- 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.