NEC Article 440 (Air Conditioning)
MrCool 12,000 BTU Mini Split: Breaker & Wire Size
The breaker, wire, and circuit for a MrCool DIY 4th Gen (E Star) 12,000 BTU (1 ton) mini split, sized straight from the manufacturer nameplate MCA and maximum breaker.
Circuit Spec
| Voltage | 115V (single-pole) |
| Minimum circuit ampacity (MCA) | 19 A |
| Maximum breaker (MOP) | 25 A |
| Installed breaker (NEC 240.6(A) / 440.22) | 25 A |
| Minimum copper wire (MrCool) | #12 Cu |
| Preferred copper wire (MrCool) | #10 Cu |
| Representative outdoor models | DIY-12-HP-C-115C25, DIY-12-HP-WMAH-115C25 |
MCA, MOP, and the minimum and preferred wire are MrCool's own nameplate figures. The installed breaker is the largest standard breaker at or below the MOP (NEC 240.6(A) / 440.22); because 25A is already a standard size, it equals the MOP. Your unit's data plate governs.
NEC Code Minimum vs the MrCool Requirement
The wire only has to carry the 19A MCA, so the bare NEC minimum (Table 310.16, 75°C copper) is #14 — smaller than the #12 MrCool lists. MrCool sizes up for the 25A breaker and voltage-drop margin. You must follow the larger manufacturer requirement (NEC 110.3(B)); the code minimum is shown only to explain the gap, not as a wire to install.
The NEC code-minimum figure is computed from this unit's MCA through NEC Table 310.16 by the same locked engine the calculator uses; the MrCool figure is the manufacturer's own minimum. When they differ, the larger manufacturer value wins.
MCA & MOCP Breaker Calculator tool live, handing back the verdict with its cited source instead of a guess. Then keep the reading as one job in the Intry app.Frequently Asked Questions
What size breaker for a MrCool 12,000 BTU mini split?
A MrCool DIY 4th Gen 12,000 BTU (1 ton) mini split takes a 25A breaker on a dedicated 115V single-pole circuit. That is the manufacturer's maximum overcurrent protection (MOP) from the nameplate, and because 25A is already a standard breaker size (NEC 240.6(A)), the installed breaker equals the MOP. Size to the data plate, never to the BTU number.
What size wire for a MrCool 12,000 BTU mini split?
MrCool specifies #12 copper minimum (#10 preferred) for the 12,000 BTU DIY, on the 25A / 115V circuit. Its nameplate MCA is 19A. The bare NEC code minimum from a 19A MCA is #14 copper (NEC Table 310.16, 75C), but the manufacturer's larger #12 governs the install (NEC 110.3(B)) for the 25A breaker and voltage-drop margin. Install #12.
How many amps does a MrCool 12,000 BTU mini split draw?
The circuit-sizing figure is the minimum circuit ampacity (MCA): 19A for the 12,000 BTU DIY. That is what the wire must carry, and it already includes the NEC 440 compressor factor. The actual running current is lower and varies with load because the inverter compressor modulates, which is why a 1-ton unit needs only a 25A circuit. Use the MCA to size the circuit.
Can a MrCool 12,000 BTU mini split run on a 115V circuit?
Yes. The 12,000 BTU DIY 4th Gen is a 115V unit on a dedicated 25A single-pole circuit (MCA 19A, #12 copper minimum). MrCool groups its 9,000 and 12,000 BTU units on one 115V electrical row, so both plug into a standard 115V branch. The 18,000 BTU and larger units step up to 208-230V.
Is the Intry MCA & MOCP breaker calculator accurate?
Every calculated figure is re-derived from its locked source before any deploy, backed by 4858 automated checks that also guard where each number comes from. A number that drifts from the cited NEC Article 440 section blocks the ship. This is our own deterministic gate, not a third-party audit. The per-tool receipt is public at https://www.intrysys.com/verified.
Source
Circuit data transcribed from the manufacturer: MrCool DIY 4th Gen E Star Installation & Owner's Manual, p.34 (Minimum Wire Gauge for Power Cables), accessed 2026-07-14. The 12,000 BTU (1 ton) DIY 4th Gen is a 115V unit: MCA 19A and a 25A maximum breaker, on a dedicated 115V / 25A single-pole circuit with #12 copper minimum (#10 preferred). It shares the exact electrical row MrCool prints for the 9,000 BTU unit.
Other MrCool DIY Mini Split Sizes
9,000 BTU (0.75 ton)
25A / 115V, #12 Cu minimum.
18,000 BTU (1.5 ton)
30A / 208-230V, #10 Cu minimum.
24,000 BTU (2 ton)
35A / 208-230V, #8 Cu minimum.
36,000 BTU (3 ton)
35A / 208-230V, #8 Cu minimum.
All Models: Breaker & Wire Chart
Every MrCool DIY size on one table: MCA, breaker, and wire, 9k to 36k BTU.
Related Tools
MCA / MOCP Calculator
Enter your unit's MCA and max breaker to get the wire, breaker, and ground.
Mini Split Wire Size (Any Brand)
Size any ductless mini split to its nameplate MCA and MOP, with typical ranges by BTU.
Can My Panel Handle It?
Before you add the circuit, the NEC 220.87 check on whether the service can carry it.