The wiring behind the AC: circuit, MCB, earthing and sanctioned load

Updated September 2, 2026 · Claude AC · 3 sources cited

Contents (8)

What an air conditioner actually draws
Decision one: a dedicated circuit
Decision two: the MCB, its rating and its curve
Decision three: cable size and the length problem
Decision four: earthing and residual current protection
Decision five: your sanctioned load with the DISCOM
A short brief for your electrician
Frequently asked questions

The machine is chosen over three weeks of comparing star ratings. The wiring that feeds it is decided in ninety seconds on installation morning, by whoever is holding the drill, by extending whatever circuit happens to be nearest. That asymmetry explains a large share of the summer complaints that get blamed on the air conditioner: the breaker that trips every evening, the socket that browns around the pins, the machine that cuts out when the fridge compressor starts.

None of this is exotic electrical engineering. It is five decisions, all of which should be made before the AC arrives, and all of which a competent electrician will recognise immediately.

What an air conditioner actually draws

Indian domestic supply is nominally 230 V, single phase. The figures below are planning indications only — the authority is the nameplate on your specific model, which prints rated and maximum input current.

Machine	Indicative running current at 230 V	Circuit usually specified
1.0 tonne inverter split	Roughly 4–6 A in steady operation	Dedicated 16 A circuit
1.5 tonne inverter split	Roughly 5–8 A, rising on pull-down	Dedicated 16 A circuit
1.5 tonne fixed-speed split	Roughly 8–10 A whenever running	Dedicated 16 A circuit
2.0 tonne inverter split	Roughly 8–11 A on pull-down	Dedicated 16–20 A circuit
1.5 tonne window unit	Roughly 8–10 A	Dedicated 16 A socket

Two behaviours matter more than the averages. A fixed-speed compressor starts at several times its running current for a fraction of a second — the surge that dims the lights and, on an undersized breaker, trips it. An inverter machine ramps up gently instead, which is easier on the circuit, but it can hold a high current for many minutes while pulling a hot room down, so it is not a licence to undersize anything. How that translates into rupees is set out in our guide to what an AC costs to run in India.

Decision one: a dedicated circuit

An air conditioner should have its own circuit from the distribution board — its own breaker, its own cable, nothing else on it. Shared with the bedroom lights and sockets, a 1.5 tonne machine leaves very little headroom, and the day someone plugs in an iron the breaker trips. Worse, the shared cable was sized for a lighting load and now carries a continuous motor load for six hours a night. A dedicated circuit also lets a technician isolate the machine at the board without darkening the room.

Decision two: the MCB, its rating and its curve

The miniature circuit breaker protects the cable, not the appliance — a distinction that explains why oversizing it is dangerous. A breaker larger than the cable can carry lets the wire overheat inside the wall before anything trips.

Rating. Sized to the cable and the machine’s maximum input current, commonly 16 A or 20 A for domestic splits. This is the electrician’s calculation, not a shop-counter default.
Curve. Motor loads are usually given a C-curve breaker, which tolerates a brief inrush without nuisance tripping while still protecting against a genuine fault. A B-curve breaker on a fixed-speed compressor is a classic source of « my AC keeps tripping the MCB ».
An isolator near the outdoor unit. A local switch lets a technician kill the supply where he is working. It is standard good practice and costs very little at installation time.

If a breaker trips repeatedly, the answer is never a bigger breaker fitted blind. It is a diagnosis: wrong curve, undersized cable, a failing capacitor or a genuine earth fault.

Decision three: cable size and the length problem

Copper cable is sized for two things at once — the current it carries, and the voltage it loses along the way. A short run to a 1.5 tonne split is commonly wired in 2.5 mm² copper; a longer run, a bigger machine or a hot conduit packed with other cables pushes that to 4 mm². These are indications; the selection belongs to the electrician working to the wiring code.

Length is the part people underestimate. Voltage drop grows with distance, and a machine at the far end of a thin, long run sees a lower voltage than the board does, which is precisely the condition that makes the question in our guide to voltage stabilisers live again — except here the cause is inside your own flat rather than out on the feeder.

Two more real failure modes:

Terminations, not cable, burn. A loose screw at the socket or the breaker creates resistance, resistance creates heat, and heat browns the plastic. Discoloured or warm socket faces are an emergency, not a cosmetic issue.
Never on an extension board. Multi-plug strips and light extension cords are not rated for a continuous motor load. The AC goes into a proper socket or is hard-wired, with nothing in between.

Decision four: earthing and residual current protection

Metal-bodied appliances are earthed so that a fault current has a path other than through a person. That obligation is the backbone of Indian electrical safety rules, and an air conditioner — a metal box, outdoors, in monsoon rain — is the least negotiable case there is.

Modern Indian wiring practice pairs that with a residual current device (RCCB, typically 30 mA for domestic circuits) which trips on the tiny leakage current that precedes a shock. Two questions to ask on installation day: is the AC circuit earthed, and is it behind an RCCB? « The building is old » is a reason to upgrade the board, not to skip either.

Warning signs worth acting on the same week

A socket or plug that is warm to touch, or discoloured around the pins.
A burning or fishy plastic smell near the board or the socket.
The breaker tripping repeatedly, or a slight tingle from the indoor unit’s casing.

Decision five: your sanctioned load with the DISCOM

Every domestic connection in India carries a sanctioned load in kilowatts, agreed with the distribution company and printed on your bill. It is not a suggestion: the service cable, the meter and the tariff category are all set against it, and drawing well beyond it can mean penal charges or a forced revision.

An air conditioner is the appliance most likely to breach it. A household sanctioned at a modest load, already running a fridge, pump, geyser and fans, can add one 1.5 tonne machine and sit at the edge — and a second machine puts it over. Enhancing the sanctioned load is a routine application to the DISCOM, usually with a revised fixed charge and sometimes a new meter or cable. Do it before the second AC, not after the third complaint.

There is a tariff consequence too. Many states bill domestic electricity in telescopic slabs, so the units an AC adds land at the top of your consumption, at the highest rate you pay — which is why the marginal cost of running one is usually higher than an average tariff suggests.

A short brief for your electrician

Sizing first — decide the tonnage with our tonnage calculator for India — then hand over four numbers: the model’s maximum input current, the cable run length from board to unit, whether the machine is inverter or fixed-speed, and your current sanctioned load. Ask for a dedicated circuit with an appropriately rated C-curve MCB, correctly sized copper, a local isolator at the outdoor unit, verified earthing and RCCB protection. Then keep the installation slip with the invoice, because the electrical work is exactly where a warranty argument starts, as our guide to AC warranty in India explains.

Frequently asked questions

Which MCB rating should an AC have?

It depends on the model’s maximum input current and the cable feeding it, which is why the honest answer is that your electrician calculates it — commonly 16 A or 20 A for a domestic split, on a C-curve breaker that tolerates compressor inrush. What you should not do is fit a larger breaker because the old one keeps tripping — that lets the cable overheat instead.

Can I run a 1.5 tonne AC on an ordinary 6 A socket?

No. A 1.5 tonne machine draws well beyond what a 6 A socket and its light circuit are built for, and the result is heat at the plug, browned contacts and eventually a failure at the socket. A window unit belongs on a dedicated 16 A socket; a split is normally hard-wired to its own circuit with a local isolator. Extension boards and multi-plugs are unsuitable in every case.

Why does my AC trip the breaker only on hot afternoons?

Because that is when the machine works hardest and draws its highest current, so a marginal circuit finally crosses the line. Common causes are a breaker rated or curved wrongly for the load, a cable undersized for its length, a condenser starved of airflow so the compressor draws more, or a failing capacitor on a fixed-speed unit. Have the current measured under load rather than guessing.