Factory-direct from Lahore · Nationwide delivery in 2–4 days
+92 319 4262451
WhatsApp
The breaker protects the cable, so either the cable comes up to the load, or the load and the breaker come down to the cable.
Both are legitimate answers and an electrician will offer you both. Replacing the run gives the capacity back and costs you the wall; dropping the MCB to the cable's rating costs nothing and takes the heavy appliance off that circuit. What is not on the list is leaving a 32 A breaker sitting on 2.5 mm² and hoping — that is the pairing that lets a wire burn without anything tripping.
A wire is too small when the current the circuit actually draws is above what the conductor can carry in the way it is installed. On BS 7671 reference method C at 30 °C, 1.5 mm² carries 19.5 A, 2.5 mm² carries 27 A, 4 mm² carries 36 A and 6 mm² carries 46 A with two loaded conductors, and every one of those figures falls in conduit, in a bundle, or in summer heat. Because the breaker's rating must sit under the cable's derated capacity, an undersized run leaves exactly two honest directions: a larger conductor, or a smaller breaker and a smaller load.
| Option | What it gives you | What it costs |
|---|---|---|
| Replace the run at the correct size | The full load back, nothing else changes | The wall opened and the run pulled again |
| Drop the MCB to the cable's rating | Correct protection the same afternoon, no rewiring | The circuit trips sooner — the heavy appliance has to come off it |
| Give the heavy appliance its own new circuit | One correctly sized run; the old cable keeps the light loads | One new run and one spare way in the board |
| Leave it as it is | Nothing | Not an option if the cable is warm, smells, or is discoloured |
In a house the third option is usually the cheapest real fix, because it is almost always one appliance — an AC point, a geyser, a kitchen circuit — that outgrew the wire, while the lighting and socket circuits behind the same board are fine. Pulling one new run from the board beats rewiring the floor.
| Size | Trade code | Capacity | Largest MCB | Circuit it then serves |
|---|---|---|---|---|
| 1.5 mm² | 3/.029 | 19.5 A | 16 A | Lights and fans |
| 2.5 mm² | 7/.029 | 27 A | 25 A | Sockets, kitchen |
| 4 mm² | 7/.036 | 36 A | 32 A | AC point, geyser |
| 6 mm² | 7/.044 | 46 A | 40 A | House submain, instant geyser |
| 10 mm² | 7/.052 | 63 A | 63 A | Meter to distribution board |
Read the table in whichever direction your problem points. Downwards, it tells you the biggest breaker a cable already in the wall may keep. Upwards, it tells you the smallest cable a load already in the house needs. What it never allows is the reverse move — fitting a bigger MCB so the tripping stops. That deletes the report and leaves the load, and the full arithmetic of that mistake is on cable overheating.
Two cases force the cable to be replaced whatever you do at the board. The first is damage already done: insulation that has gone brown, tacky or brittle from running hot has lost life it does not get back, and a smaller MCB will not restore it. The second is length. A cable can be comfortably inside its current rating and still deliver too little voltage at the far end — 2.5 mm² carries 27 A, but at 20 A over a 30 m run it loses 10.8 V, nearly 5% of 220 V. A smaller breaker does nothing about that; only a bigger conductor does. The run-length limits by size are on voltage drop.
Before you buy anything, check that the cable in the wall is the size it was sold as. Under-section coils and copper-clad aluminium are common enough in Pakistan that a circuit can be undersized without anyone having chosen the wrong number — the weight check for a coil is on the overheating page, and we will check conductor size and resistance on a sample.
We draw the copper in Lahore and sell it at the day's rate — no dealer margin. Send the load, the run length and your city: Punjab in 1–2 days, rest of Pakistan in 2–4. Where the answer is 4 mm², that is 4mm 3 core standard cable.