What Wire Size Do You Need for an AC?
As a quick rule for Indian homes, a 1 ton AC runs happily on 2.5 sq mm copper, a 1.5 ton on 4 sq mm, and a 2 ton on 4 to 6 sq mm, each on its own dedicated circuit. Getting this right keeps the compressor healthy through the long Tricity summer and protects against the voltage swings common in the region.
What wire size do I need for an AC?
Use 2.5 sq mm copper for a 1 ton, 4 sq mm for a 1.5 ton, and 4 to 6 sq mm for a 2 ton, each on its own dedicated circuit with a C-curve MCB. Step up a size on long runs.
01Why an AC needs a dedicated circuit
An air conditioner is one of the heaviest loads in a home and it draws a big surge every time the compressor starts. Sharing that circuit with sockets or lights means flickering, nuisance tripping, and a cable that runs hot. A dedicated circuit, its own cable running straight from the board to the AC point, isolates that surge and lets the wire and breaker be sized precisely for the job.
It also makes fault finding simple and safe. If the AC develops a problem, its own MCB trips without knocking out the rest of the room, and the unit can be fully isolated for service.
A dedicated line should ideally include its own isolator near the indoor unit so the technician can work with the circuit completely dead. During the fierce Tricity summer an air conditioner may run for many hours at a stretch, and that sustained load is exactly what a shared socket circuit was never designed to carry safely.
02Wire size by tonnage
Cooling capacity is rated in tons, and the bigger the unit the more current it pulls, so the cable must grow with it. A 1 ton split typically needs 2.5 sq mm copper, a 1.5 ton needs 4 sq mm, and a 2 ton needs 4 to 6 sq mm depending on run length and whether it is a power hungry fixed speed model. Window units of the same tonnage draw similar current and follow the same sizing.
These are starting points for a short run at 230V. Always cross check the current on the AC rating plate, and if the unit is far from the board or the wiring is old, step up a size for margin.
Inverter and fixed speed models of the same tonnage draw broadly similar peak current, so the cable sizing is much the same for both. What changes is the running pattern, since an inverter modulates its compressor rather than cycling fully on and off, but the wire must still be rated for the peak the unit can pull on a hot afternoon.
03The right MCB: C-curve
An AC compressor draws a large inrush current for a fraction of a second at start up. A standard B-curve MCB, which trips at three to five times its rating, may see that surge as a fault and trip every time the AC kicks in. A C-curve MCB trips at five to ten times its rating, so it rides through the normal starting surge but still protects the cable against a real fault.
Match the MCB rating to the cable, not the appliance: a 4 sq mm AC circuit usually takes a 20A C-curve breaker. Pair it with a 30mA RCCB at the board for shock protection.
04Stabiliser versus inverter AC
Tricity voltage can sag on hot evenings when everyone's cooling is running, and a fixed speed AC often needs an external stabiliser to protect its compressor from low or fluctuating voltage. If you fit one, remember the stabiliser also sits on that dedicated circuit and must be wired for the same load.
Modern inverter ACs have a wide input voltage range built in and usually run without a separate stabiliser, which is one reason they suit areas with unstable supply. Even so, the cable and MCB sizing stays the same, because the running and starting currents are broadly comparable.
05Run length and derating
The distance from the board to the outdoor point matters. A long cable run drops voltage and gets warmer, both of which stress the AC. If the run is more than about fifteen metres, or the cable is bunched with others in a hot conduit, step up one size to keep voltage healthy and the wire cool.
- Short run under 10m: use the base size for the tonnage.
- Run of 15m or more: consider one size up.
- Cable bunched in a hot conduit: derate and size up.
- Old or brittle existing wiring: replace rather than reuse for a new AC.
06Common AC wiring mistakes
The classic error is running a new AC off a nearby 6A socket circuit on 2.5 sq mm, which is only safe for the smallest units and often not even then. Another is using a B-curve MCB that trips on every start, then oversizing it to compensate and leaving the cable unprotected. Both put the compressor and the wiring at risk.
Do it properly: a dedicated copper circuit sized to the tonnage, a C-curve MCB matched to the cable, RCCB protection, and a size up for long runs. It is a small job at installation that prevents years of tripping and premature compressor wear.
It is also worth planning the AC point before the walls are finished, because the outdoor unit, the drain and the power all want to arrive at the same spot. Deciding the tonnage early lets the electrician lay the correct cable first time, rather than chasing a thin existing wire into service for a load it cannot handle.
AC wire and MCB sizing by tonnage (230V, dedicated circuit)
| AC size | Copper wire | MCB (C-curve) | Notes |
|---|---|---|---|
| 1.0 ton | 2.5 sq mm | 16A | Own circuit from board |
| 1.5 ton | 4 sq mm | 20A | Most common split size |
| 2.0 ton | 4 to 6 sq mm | 20 to 25A | 6 sq mm on long runs |
| Any, run over 15m | One size up | Match to cable | Limits voltage drop |
| Fixed speed unit | As above | As above | May need a stabiliser |
Frequently asked questions
What wire size do I need for an AC?
Use 2.5 sq mm copper for a 1 ton, 4 sq mm for a 1.5 ton, and 4 to 6 sq mm for a 2 ton, each on its own dedicated circuit with a C-curve MCB. Step up a size on long runs.
Why does an AC need a C-curve MCB?
The compressor draws a big surge at start up. A C-curve MCB rides through that surge without nuisance tripping while still protecting the cable against a genuine fault.
Does an AC need its own circuit?
Yes. A dedicated circuit isolates the heavy starting surge, prevents flickering and tripping, and lets the cable and breaker be sized exactly for the unit.
Do I still need a stabiliser?
A fixed speed AC often needs one where voltage fluctuates, as it can in the Tricity. Most inverter ACs have a wide voltage range built in and usually run without one.
Can I run my AC off a normal socket?
Only the smallest 1 ton units, and even then a dedicated circuit is far safer. Larger ACs must have their own properly sized copper circuit.
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