Which MCB for an AC: read the nameplate, not the tonnage
A 1.5 ton AC does not draw 5,275 W. That is the heat it moves. The current it draws is printed on the nameplate, and it is a fraction of that. That is the number the MCB and the wire are chosen from.
By Bulan Sarkar · Updated
Find the rated current on the outdoor unit's nameplate, and the maximum current if it lists one. Take the higher of the two. The MCB is the next standard rating at or above it from IS/IEC 60898-1: 6, 10, 16, 20, 25, 32 A. A plate showing 10.5 A maximum needs a 16 A MCB. Don't work from the tonnage: 1.5 tons is 5,275 W of cooling, not of electricity. The AC gets its own circuit, because CPWD gives every load over 1 kW its own MCB, on at least 4 sq mm copper.
Source: IS/IEC 60898-1:2002 Circuit-breakers for overcurrent protection for household and similar installations, checked Oct 2026.
What the nameplate says, line by line
The nameplate is the printed sticker or metal plate on the outdoor unit of a split AC (on the side of a window AC). The installation manual repeats it. The lines that matter for wiring:
- Rated voltage and frequency: 230 V, 50 Hz, single phase for almost every home AC.
- Cooling capacity, in W or kW: the heat the AC removes from the room. It is not electricity, so leave it out of the wiring sum.
- Rated power input, in W: the electricity drawn while cooling at the rated test condition. This is the figure for your connected load.
- Rated current, in A: the current at that condition.
- Maximum current or maximum input, on many plates: what the AC can draw on the hottest days, when the compressor works hardest. If the plate lists it, size the MCB on it.
Some manuals also name a breaker or fuse size. If yours does, use the higher of that figure and the one you work out below.
From the nameplate to the MCB and the wire
IS/IEC 60898-1 cl. 5.3.2 lists the preferred MCB ratings: 6, 8, 10, 13, 16, 20, 25, 32, 40, 50 and 63 A, and up. Shops mostly stock 6, 10, 16, 20, 25 and 32 A. Take the next rating at or above the AC's highest current.
| Highest current on the plate | MCB | Minimum copper wire |
|---|---|---|
| up to 6 A | 6 A | 4 sq mm |
| 6.1 to 10 A | 10 A | 4 sq mm |
| 10.1 to 16 A | 16 A | 4 sq mm |
| 16.1 to 20 A | 20 A | 4 sq mm |
| 20.1 to 25 A | 25 A | 4 sq mm |
The wire must carry at least what the MCB lets through (IS 732 cl. 5.3.3.2: design current ≤ MCB rating ≤ wire rating). CPWD cl. 3.12 puts power wiring at 4 sq mm copper minimum, which covers MCBs up to 25 A on our wire table (IS 3961 Part 5, in conduit, × 1.23 for MCB protection). Above that, or on a long run, use the wire size calculator.
CPWD also asks for an industrial-type socket with its own MCB for any outlet above 1 kW (cl. 3.11 iii). It recommends a double-pole MCB in an enclosure as the outlet for a window AC or a geyser (cl. 3.14 a iii), which cuts both the live and neutral wires.
Why tonnage is the wrong number
A "ton" on an AC is a ton of refrigeration: 12,000 BTU an hour, which NIST lists as 3,516.853 W. It measures the heat the AC pumps out of the room. A 1.5 ton AC moves about 5,275 W of heat. It uses far less electricity than that, because a compressor moves several watts of heat for each watt it draws. That ratio, averaged over a season, is what the star rating is based on.
| AC size | Cooling, W | If misread as electrical load, A at 230 V |
|---|---|---|
| 1 ton | 3,517 | 15.3 |
| 1.5 ton | 5,275 | 22.9 |
| 2 ton | 7,034 | 30.6 |
The right-hand column is the mistake. A 1.5 ton AC that really draws 6.9 A, wired as if it drew 22.9 A, gets a 25 A MCB. If that MCB sits on 2.5 sq mm wire, it can let more current through than the wire is rated for. A bigger MCB is not a safer one.
Worked examples
1. 1.5 ton inverter split, plate shows rated and maximum current
- Sample nameplate: 230 V, 50 Hz; cooling 5,100 W; rated input 1,540 W; rated current 6.9 A; maximum current 10.5 A
- Higher current: 10.5 A
- Next standard MCB at or above 10.5 A: 16 A (13 A is in the standard but rarely stocked)
- Wire: 4 sq mm copper (CPWD minimum for power; rated well above 16 A in conduit)
- For the connected load, use the rated input: 1,540 W
Result: 16 A MCB on its own circuit with 4 sq mm wire. In the electrical load calculator, enter 1,540 W and 10.5 A for this AC.
2. Plate shows only the rated current
- Sample nameplate: 230 V; rated input 1,650 W; rated current 7.5 A; no maximum listed
- Next standard MCB at or above 7.5 A: 10 A
- Manual says "breaker: 16 A"
- Higher of the two: 16 A
Result: 16 A MCB, because the maker's figure is higher. Without the manual's figure, 10 A would be the minimum by the rule, and 4 sq mm wire covers either.
3. Plate shows watts but no amps
- Sample nameplate: 230 V; rated input 1,700 W; current not shown
- 1,700 ÷ 230 = 7.4 A as a floor
- The real current is higher than this, because an AC's power factor is below 1
- Next standard MCB above 7.4 A: 10 A at the least
Result: Treat 10 A as the minimum and look up the rated and maximum current in the manual or on the maker's website before buying the MCB. If the maximum turns out above 10 A, step up to 16 A.
Tips and tricks
- Photograph the nameplate before the outdoor unit goes up on the wall bracket. Reading it later means a ladder or a rope.
- Size the MCB on the maximum current if the plate lists one. The rated current is measured at a test condition that a 45 °C May afternoon will exceed.
- Give every AC its own circuit and MCB. Two ACs on one 16 A circuit with a 4-way extension board is the setup that keeps tripping.
- Run 4 sq mm wire to each future AC point during the first wiring, even if the AC is a year away. A 1 ton AC now may be a 2 ton AC later.
- Write the AC's MCB rating and its room on the board label, so nobody swaps in a bigger MCB when it trips.
What we would do
We'd read the nameplate at the shop or from the manual before the AC is installed, take the maximum current if it is listed, and ask for the next standard MCB on its own circuit with 4 sq mm copper. We'd ask the electrician which curve, B or C, they plan to fit and why. If the AC keeps tripping, we'd have the circuit checked rather than fit a bigger MCB.
Frequently asked questions
Which MCB is used for a 1.5 ton AC?
How many amps does a 1.5 ton AC draw?
What wire size is used for an AC point?
Sources and date checked
- IS/IEC 60898-1:2002, Circuit-breakers for overcurrent protection for household and similar installations: cl. 5.3.2 preferred rated currents, Table 2 instantaneous tripping ranges (B, C, D). Checked Oct 2026.
- CPWD General Specifications for Electrical Works, Part I (Internal), 2013: cl. 3.10 (iv) loads over 1 kW, 3.11 (iii) sockets above 1 kW, 3.12 cables, 3.14 (a)(iii) double-pole MCB for AC and geyser outlets (copy hosted by the Directorate General of Lighthouses and Lightships). Checked Oct 2026.
- IS 732:1989, Code of practice for electrical wiring installations: cl. 5.3.3.2 (design current ≤ device rating ≤ cable rating). Checked Oct 2026.
- IS 3961 (Part 5):1968, Recommended current ratings for PVC insulated light duty cables: Table 1 and Table 8 (factor for close excess-current protection). Checked Oct 2026.
- NIST Guide to the SI (SP 811), Appendix B.9: ton of refrigeration (12,000 BTU per hour) = 3,516.853 W. Checked Oct 2026.
This guide covers reading a nameplate and choosing ratings on paper. Switch off the supply and check the circuit is dead with a tester before anyone opens a board or a socket. Follow your state's wiring rules, and use a licensed electrician to install the circuit and the MCB wherever the law requires one. Earthing and the RCCB are the electrician's job; the AC itself is installed by the maker's technician.