Electrical / runnable MCP tool
Run the MCA & MOCP Breaker 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: mca_mocp.
How it computes the answer
From an HVAC nameplate MCA and MOCP, or from compressor RLA and fan FLA in RLA mode: the minimum wire size from NEC 310.16 at the ambient Table 310.16 itself assumes, with 3 or fewer current-carrying conductors, the breaker as the largest standard 240.6(A) rating not exceeding MOCP per 440.22, the ground from 250.122, and voltage drop.
What it cites
Your assistant calls the same engine the interactive calculator calls, with the inputs listed under Inputs. It sizes the conductor at 86 F, the ambient Table 310.16 itself assumes, with 3 or fewer current-carrying conductors and insulation rated at the termination temperature you give, so no ambient correction (Equation 310.15(B)(1)), bundling adjustment (Table 310.15(C)(1)) or rooftop adder (310.15(B)(2)) is applied here. This tool takes no ambient, conductor count or insulation input; the web calculator takes them (with a rooftop run) and resizes the conductor. These are the sources that engine reads, including the ones for inputs only the interactive calculator takes.
- NEC 440.33, 440.34, 440.35 and 430.24
- Minimum circuit ampacity, when computed from RLA/FLA: 125% of the largest motor-compressor or motor full-load current plus 100% of the others in the group (440.32 governs a lone compressor, the same 125% result). NEC 440.34 governs instead once a non-motor load such as strip heat shares the circuit, and NEC 440.35 is the ampacity the conductor must reach. In nameplate mode you enter the marked MCA directly. NFPA 70-2023, p. 70-369 / p.70-345.
- NEC 440.22, 440.22(A) and 440.22(B)(1)
- Maximum overcurrent protection: the branch-circuit short-circuit and ground-fault device, the largest standard rating that does not exceed the calculated maximum. 440.22(A) is the ceiling for an INDIVIDUAL motor-compressor, 175% of its rated-load current or branch-circuit selection current and 225% where the motor will not start on 175%. Where other loads share the circuit, 440.22(B)(1) permits that value PLUS the sum of those other loads, and the tool applies Exception No. 1's round-up to the next standard rating and Exception No. 3's 15 A floor. Fetched from the primary (p.70-368).
- NEC 240.6(A)
- Standard overcurrent-device ratings. The recommended breaker is the largest standard rating at or below the MOCP ceiling (and, where minimum-sizing applies, the smallest standard rating at or above the MCA). Fetched from the primary.
- NEC 240.4(G) (Article 440)
- Air-conditioning and refrigeration branch-circuit conductors are protected under Article 440, so they are exempt from the 240.4(D) small-conductor overcurrent cap. This exemption applies inside Article 440 only, never on a general branch circuit. Fetched from the primary (p.70-124).
- NEC 440.1, 440.21, 424.4(B) and 424.19 (a circuit with no compressor)
- Article 440's special provisions, including the Part III overcurrent relief Table 240.4(G) points to, are for circuits supplying a hermetic refrigerant motor-compressor (440.1, 440.21). When you say no compressor is on the circuit (or, in the calculator's RLA mode, leave the compressor RLA at 0; over MCP, answer that no compressor is on the circuit), this tool does not size it: an air handler's heat strips and blower on their own circuit are Article 424, where 424.4(B) sizes the conductors at 125% of the heater and blower and Table 240.4(G) has no row, so it sends you to the heat strip calculator, and its disconnect is 424.19's (rated at least 125 percent of the motor and heater load, lockable, within sight of the unit's supplementary devices), never 440.14's. Read from the NFPA 70-2023 primary (p.70-365, p.70-368, p.70-323).
- NEC 310.15(B)(1) and 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 310.15(B)(2)
- The rooftop option. For raceways or cables in direct sunlight where the distance above the roof to the bottom of the raceway is less than 19 mm (3/4 in), a temperature adder of 33 C (60 F) is added to the outdoor temperature. Type XHHW-2 conductors are excepted. NFPA 70-2023, p. 70-184.
- 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 tool sizes on the column you choose, and where the answer holds only on 75°C terminations it says so beside it. This is the cap most calculators skip.
- NEC 440.14, 440.12 and 110.26(A)
- The disconnecting means: within sight from and readily accessible to the equipment (NEC 440.14), rated by NEC 440.12, with the working space of 110.26(A) preserved. This tool prints the requirement and does NOT check it: nothing here has been anywhere near the equipment, so the row says so in the row itself. The horsepower tables NEC 440.12 sends you to (NEC Table 430.248 and Table 430.251) are named for the same reason, cited and not read.
- NEC 440.52
- Compressor overload protection. On an Article 440 circuit the branch-circuit device covers short circuits and ground faults while the equipment's own overload protection, required by 440.52 and verified by the listing, is what protects the conductor. This is why 240.4(G) can relieve the 240.4 conductor rule inside Article 440 and nowhere else.
- NEC Table 310.16
- Conductor ampacity for the minimum circuit ampacity, the general ampacity table for conductors in raceway or cable, held to the termination column per 110.14(C). Fetched from the primary (p.70-187).
- NEC Table 250.122
- Equipment grounding conductor, sized from the circuit's overcurrent device. NFPA 70-2023, p. 70-158.
- NEC 440.4(B) and 110.3(B)
- The nameplate minimum circuit ampacity and maximum overcurrent rating marked on the equipment govern; the manufacturer's marking is the field ceiling under 110.3(B). Fetched from the primary.
- NEC Chapter 9 (voltage drop) and 210.19(A)
- The voltage-drop reading reuses the voltage-drop engine: conductor circular mils from NEC Chapter 9 Table 8 against the advisory 3% recommendation (210.19 Informational Note, guidance, not an enforceable limit).
These are NEC Article 440 rules and referenced tables, applied by the engine to the nameplate values you enter and to the conditions you state, not measurements. The conditions have defaults and the tool says which it used; state yours and the conductor can change. When the nameplate marks MCA and MOP, those markings govern the install; the engine's code-minimum output is a check, and the AHJ has final say.
The full receipt, with every source and how each is cross-checked, is on the interactive MCA & MOCP Breaker Calculator.
Ask your assistant
The one rule that makes it reliable: name Intry in your question. That is what tells Claude to run the mca_mocp 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 |
|---|---|---|---|
| mode | optional | nameplate, rla | nameplate (enter MCA/MOCP) or rla (enter loads). Default nameplate. |
| mca | optional | number | Minimum circuit ampacity from the nameplate. Required in nameplate mode (the default): an empty request is refused rather than sized from a default circuit. To size from compressor RLA and fan FLA instead, pass mode: 'rla' with loads. |
| mocp | optional | number | Maximum overcurrent protection from the nameplate. |
| loads | optional | array | MOTOR loads only in rla mode, the compressor RLA FIRST, then fan FLA; the largest gets the 125% factor per NEC 440.33. For a circuit with no compressor (an air handler's strips and blower), pass compressorOnCircuit: false instead: this tool cannot tell a blower from a compressor. |
| compressorOnCircuit | optional | boolean | Is a hermetic compressor on this circuit? Default true. false is refused with a pointer to the heat strip calculator: Article 440's relief (Table 240.4(G)) is for circuits supplying a compressor (440.1, 440.21), and an air handler's strips and blower are Article 424, where 240.4(D) holds #10 copper to 30 A. |
| otherNonMotorAmps | optional | number | Any NON-motor load on the COMPRESSOR's circuit (strip heat in a packaged unit, crankcase heater). NEC 440.34 governs once this is present, so it must not be passed inside loads[]. |
| voltage | optional | number | Circuit voltage (default 240). |
| phase | optional | single, three | Default single. |
| distance | optional | number | One-way run feet for a VD check; 0 skips it (default 0). |
| material | optional | cu, al | Default cu. |
| tempRating | optional | 60, 75 | Termination temperature rating (default 75). |
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 Article 440 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.