Central Air Conditioner: Complete Wiring Guide
Bill of materials
Central AC and heat pump circuits follow NEC Article 440 for motor-compressor loads. The nameplate on the outdoor unit specifies the minimum circuit ampacity (MCA) and maximum overcurrent protective device (MOCP). Wire size must meet MCA; breaker size must not exceed MOCP. These numbers are on the equipment data plate.
Air conditioner circuits use Article 440, not standard branch circuit rules. The MCA (minimum circuit ampacity) on the nameplate determines minimum wire size. The MOCP (maximum overcurrent protective device) determines maximum breaker size. Never exceed the MOCP. A disconnect within sight of the outdoor unit is required per 440.14. The flexible metallic conduit "whip" from the disconnect to the unit is typically 6 feet of 10 AWG or 8 AWG THHN.
2-ton AC (15A circuit)
| Component | Specification | NEC basis |
|---|---|---|
| Wire (copper) | 14 AWG THHN | Table 310.16, 110.14(C) |
| Wire (aluminum alt.) | 12 AWG THHN | Table 310.16, 110.14(C) |
| Breaker | 15A double-pole | 240.4 |
| Voltage | 240V single-phase | |
| Conduit (EMT) | 1/2" EMT | Chapter 9 Table 4 |
| Max distance (3% VD) | 95 ft at 240V copper | 210.19(A) Note 4 |
3-ton AC (25A circuit)
| Component | Specification | NEC basis |
|---|---|---|
| Wire (copper) | 10 AWG THHN | Table 310.16, 110.14(C) |
| Wire (aluminum alt.) | 8 AWG THHN | Table 310.16, 110.14(C) |
| Breaker | 25A double-pole | 240.4 |
| Voltage | 240V single-phase | |
| Conduit (EMT) | 1/2" EMT | Chapter 9 Table 4 |
| Max distance (3% VD) | 161 ft at 240V copper | 210.19(A) Note 4 |
5-ton AC (40A circuit)
| Component | Specification | NEC basis |
|---|---|---|
| Wire (copper) | 8 AWG THHN | Table 310.16, 110.14(C) |
| Wire (aluminum alt.) | 6 AWG THHN | Table 310.16, 110.14(C) |
| Breaker | 40A double-pole | 240.4 |
| Voltage | 240V single-phase | |
| Conduit (EMT) | 3/4" EMT | Chapter 9 Table 4 |
| Max distance (3% VD) | 164 ft at 240V copper | 210.19(A) Note 4 |
Installation notes
GFCI is not specifically required for this application by NEC, though local amendments may differ. Check with your local building department before starting work.
For the wire run, you have two options: NM-B cable (Romex) for interior runs through framing, or individual THHN conductors in conduit for exposed runs, outdoor installations, or runs through unfinished spaces. NM-B is faster to install but cannot be used outdoors or in conduit. For conduit, use EMT (metallic) or PVC Schedule 40.
Run length matters: every foot of wire adds voltage drop, reducing power to your equipment. The table below shows the exact voltage drop at common distances. If your run exceeds the 3% threshold, upsize one gauge.
Voltage drop by distance
Percentage voltage drop at common run lengths. NEC recommends 3% maximum for branch circuits and 5% for combined feeder plus branch.
| Distance | 14 AWG Co | 12 AWG Al | 12 AWG Co |
|---|---|---|---|
| 25 ft | 0.8% | 0.8% | 0.5% |
| 50 ft | 1.6% | 1.6% | 1.0% |
| 75 ft | 2.4% | 2.4% | 1.5% |
| 100 ft | 3.1% | 3.2% | 2.0% |
| 150 ft | 4.7% | 4.9% | 3.0% |
| 200 ft | 6.3% | 6.5% | 4.0% |
Common products for 14 AWG Copper circuits
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Related wire data
Detailed ampacity: 14 AWG copper, 12 AWG aluminum. Wire size lookup: 15A circuit. Calculators: voltage drop · panel load calculator.
Frequently asked questions
What wire size do I need for central air conditioner?
Use 14 AWG copper or 12 AWG aluminum on a 15A breaker at 240V. This is based on NEC 2023 Table 310.16 ampacity with 110.14(C) termination limits and 125% continuous load sizing per 210.19(A)(1).
Does central air conditioner require GFCI?
No. GFCI is not required for this application.
NEC 2023 references verified April 2026