One run
Voltage drop calculator
Enter the copper class, the current and the one-way metres. The drop uses IEC 60228 class 2 copper resistance, corrected from 20°C to 70°C. It is not a current rating from a Havells coil.
Drop on 2.5 sq mm
3.7%
8.5 V of 230 V. Over a 3% check. Within 5%.
| Class | Drop |
|---|---|
| 1.5 sq mm | 13.9 V · 6.0% |
| 2.5 sq mm | 8.5 V · 3.7% |
| 4 sq mm | 5.3 V · 2.3% |
| 6 sq mm | 3.5 V · 1.5% |
| 10 sq mm | 2.1 V · 0.9% |
| 16 sq mm | 1.3 V · 0.6% |
| 25 sq mm | 0.8 V · 0.4% |
These figures are for planning. Cable size, the breaker and the final list have to be confirmed against the drawing, the load and the Havells datasheet.
More planning tools
House wiring costTurn rooms into points, wire length and a total once you add rates.Wire sizeStart from the circuit class, then step up if the run drops too much voltage.Wire quantityTurn planning metres into 90 m Havells Lifeline Plus coils.MCB selectorPick a standard breaker rating that stays within the wire class.Connected loadAdd appliance watts from the nameplate and see the total amps.Material listWrite the coils, points and board into a list you can send on WhatsApp.
Reading the drop
Which length do I enter?
The one-way route from the distribution board to the point, in metres. The return conductor is already in the single-phase formula.
What do 3% and 5% mean here?
They are the two planning checks shown on the page. Lighting on the wire-size tool uses 3%, and other circuits use 5%. Neither figure is a utility approval.