Which Wire for AC and Geyser Points: 1.5, 2.5, 4 or 6 sq mm?

Which wire for AC: the short answer

Which wire for an AC or a geyser is decided in a fixed order: first the current the appliance draws, then the MCB its circuit needs, then a wire that, as it is actually laid, carries at least that MCB’s rating, then a check that the run is not so long that the voltage sags.

Read against our catalogue’s current table for wire in conduit, that order gives a pattern. A 16A circuit needs at least the 2.5 sq mm size, which our catalogue rates at 18 A in conduit. A 20A circuit needs at least 4 sq mm, rated 24 A. A 25A circuit needs 6 sq mm, rated 31 A. The 1.5 sq mm size, rated 13 A in conduit, sits below a 16A MCB.

That is a reading of a table, not a design. Your electrician adjusts it for the length of the run, how many cables share a pipe, the heat around it and the AC’s own manual, under IS 732. We make the MCBs, DP switches and sockets at our works in Marol, Andheri East, Mumbai; our VIYONA wire is made for us by a partner to IS 694.

Why the MCB, not the tonnage, decides the wire

The MCB decides the wire because an MCB exists to protect the cable behind it: it must trip before that cable overheats, so the cable, as installed, has to carry at least the MCB’s rating, whatever appliance is plugged in at the far end.

That gives the one rule worth remembering: wire as installed ≥ MCB rating. Break it and a 16A MCB on 1.5 sq mm wire in conduit lets 14 or 15 amps flow for hours through a wire our catalogue rates at 13 A. Nothing trips. The insulation slowly cooks inside the wall.

Tonnage is cooling capacity, not current. Two 1.5 ton ACs from different makers can draw quite different currents. The AC’s nameplate input watts and the breaker in its manual are the numbers that feed the sum.

The MCB ratings themselves are set out in our guides to the MCB for 1, 1.5 and 2 ton AC and which MCB for home: commonly 16A for a 1 ton AC, 16A–20A for 1.5 ton, 20A–25A for 2 ton, and 16A–20A for a geyser.

How much current does an AC or geyser draw?

An AC or geyser draws its input power divided by the supply voltage, so at 230 V a 1,500 W AC input draws about 6.5 A, a 2,000 W storage geyser about 8.7 A and a 3,000 W geyser about 13 A, and the MCB and wire are then chosen above that running figure.

Two things push the MCB, and so the wire, above these figures. A fixed-speed AC compressor draws a brief surge at every start. And a geyser or AC runs for hours in summer, which is the condition wire ratings are written for. That is why a 13 A geyser sits on a 16A or 20A circuit, not a 13A one. The watts behind each appliance are in our appliance power consumption chart.

Which wire for a 1.5 ton AC?

A 1.5 ton AC on a 16A MCB needs wire that carries at least 16 A as installed, which in our catalogue’s in-conduit table is 2.5 sq mm at 18 A; on a 20A MCB it needs at least 4 sq mm, rated 24 A in conduit, with the electrician confirming against the run length and the AC’s manual.

So the question to ask is which MCB? first. If the manual and the electrician settle on 16A with a 16A socket, the table points to 2.5 sq mm. If they settle on 20A, with the AC wired to a 20A switch or a 32A DP switch, the table points to 4 sq mm.

A 1 ton AC on a 16A circuit follows the same reading: 2.5 sq mm, with phase, neutral and earth in every run. Each AC gets its own circuit. Sizes, coils and MRPs for each wire are in our house wire price list.

Is 4 sq mm wire needed for an AC?

4 sq mm wire is needed for an AC when its circuit takes a 20A MCB, as many 1.5 and 2 ton units do, because our catalogue rates 2.5 sq mm at 18 A in conduit and 4 sq mm at 24 A; it also suits long runs where 2.5 sq mm loses too much voltage.

When 4 sq mm comes up: a 20A MCB on the circuit; a 2 ton AC; a long run from the board, such as a living room AC at the far end of a flat; and several cables sharing one conduit, which lowers what each can carry.

A 25A MCB goes past 4 sq mm in conduit (24 A) in our table, to 6 sq mm at 31 A. That is the reading for a large 2 ton unit whose manual asks for 25A.

Planning a bigger AC later? Running 4 sq mm to the AC point at the wiring stage costs a little more wire and nothing else. Running it after the walls are plastered means chasing them again.

Wire size for geyser

The wire size for a geyser follows its MCB: a 2,000 W storage geyser drawing about 8.7 A is commonly given a 16A circuit, which by our catalogue’s in-conduit table needs at least 2.5 sq mm, while a 3,000 W geyser or one on a 20A circuit needs at least 4 sq mm, rated 24 A in conduit.

Storage geysers are 2,000–3,000 W typically, and run their element for long stretches, which is the hardest test a wire gets. Instant geysers typically draw 3,000 W or more while water flows; read the nameplate and the manual, which states the breaker it expects.

A geyser point is usually wired to a DP switch with indicator high on the bathroom wall, or a 16A socket outside the wet zone. Our geyser switch guide covers the switch; VIZA V1250 is a 32A DP switch with indicator at ₹330 MRP.

Bathrooms add one more requirement: protection against shock, which an MCB does not give. Ask your electrician about an RCCB on bathroom circuits. We do not make RCCBs.

1.5 vs 2.5 sq mm: can 1.5 sq mm wire run an AC or geyser?

1.5 sq mm wire should not feed an AC or geyser on a 16A circuit, because our catalogue rates it at 13 A in conduit, below the 16A MCB that protects such a circuit; 2.5 sq mm, rated 18 A in conduit, is the smallest of our sizes that covers a 16A MCB.

The difference in copper is real: our catalogue gives a maximum resistance of 12.10 ohms per km for 1.5 sq mm and 7.41 for 2.5 sq mm, so 1.5 sq mm turns more of the same current into heat.

Where 1.5 sq mm belongs: light and fan circuits, commonly on a 6A or 10A MCB. Where it does not: AC, geyser, induction, microwave, or any 16A point.

The common shortcut is an AC added to an old bedroom point that was wired in 1.5 sq mm for a table fan and a lamp. The AC works. The wire runs warm every summer night. Our guide to the signs a house needs rewiring covers how that shows up.

Long runs: why distance changes the wire size

Distance changes the wire size because every metre of copper adds resistance, so a long run to a far AC or geyser loses voltage under load, and a thicker wire with lower resistance per km keeps that loss small; the electrician checks the drop for each long heavy run.

An example, using our catalogue’s maximum resistance at 20°C: a point 20 m from the board means 40 m of copper out and back. At a 10 A AC load, the drop on each size works out as shown.

Double the run, double the drop. A compressor starting on a long, thin run sees an even deeper dip for a moment, which is one reason AC circuits on long runs move up a size. Our voltage stabilizer guide covers drop from the grid side.

Many wires in one pipe: grouping and heat

Several circuits sharing one conduit carry less current each than a single circuit would, because the wires heat one another and the pipe sheds that heat slowly, so an electrician may choose a larger size for an AC or geyser run that shares a crowded pipe or passes through a hot roof or loft.

Our catalogue’s figures are for two cables of one single phase circuit, in conduit or trunking, or clipped direct. Pack the phase and neutral of three or four circuits into one pipe and each pair is working in warmer air than the table assumes.

Where this bites in a flat: the pipe from the board to the first junction, which can carry every circuit at once, and runs through a sun-baked terrace slab. Separate conduits for the AC and geyser circuits are common practice for that reason.

Grouping and temperature corrections are part of sizing under IS 732, which is your electrician’s job. Our types of wiring system guide compares conduit, casing-capping and surface systems.

What does the heavier wire cost?

Moving an AC circuit up from 2.5 sq mm to 4 sq mm costs about ₹24 more per metre of each conductor at our 90 m coil MRPs, roughly ₹49 against ₹73, so a 20 m run with phase, neutral and earth adds about ₹1,440 in wire at the wiring stage.

The sum, approximate: 60 m of conductor for a 20 m three-wire run. 2.5 sq mm about ₹2,940; 4 sq mm about ₹4,380. VIYONA 653 (2.5 sq mm) is ₹4,384 MRP for a 90 m coil and VIYONA 654 (4 sq mm) is ₹6,544.

Against a wall that has to be chased and replastered later, the heavier wire is the cheap option. Wire is sold by the coil; the full 45 m and 90 m list is on our VIYONA electrical wire page.

Switch, socket and MCB that pair with the wire

The wall point and the MCB must both match the wire: a 16A circuit on 2.5 sq mm takes a 16A socket and a 16A MCB, while a 20A or 25A circuit on 4 or 6 sq mm takes a 20A switch or a 32A DP switch with the appliance wired in, because the wall point must be rated at least as high as the MCB.

From our range, as printed in the catalogue: VIYONA 401 single pole 10 kA MCB, 6–32A, ₹145; VIYONA 411 double pole, ₹350. On the wall, VIZA V263 16A socket ₹160, KEMPS K147 20AX switch ₹120, VIZA V1250 32A DP switch with indicator ₹330, and for non-modular boards the VIYONA 175 surface DP switch ₹195 and 176 concealed ₹205.

A 20A MCB feeding a 16A socket leaves the socket as the weak point. A 32A DP switch on 1.5 sq mm wire looks heavy-duty and protects nothing. Our DP switch guide explains when a DP switch is the right wall point.

Old wiring and a new AC or geyser

Before a new AC or a bigger geyser goes on an old point, have an electrician read the wire size at the board and check the run, because a point wired years ago for a fan or a smaller unit is often 1.5 sq mm or worn, and no MCB change makes an undersized wire safe.

Warning signs on an existing point: a warm switch or socket, a brown plug top, an MCB that trips on hot afternoons, or lights that dim when the compressor starts. Each one says the wire, a joint or the point is working too hard.

Adding heavy loads also changes the total for the house. Our electrical load calculation guide adds them up against your sanctioned load and main MCB.

Work on any AC or geyser circuit starts with the MCB off and the circuit tested dead, and the wiring is for a licensed electrician.