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Voltage Drop Calculator
Voltage drop is what makes a borewell pump run hot, a top-floor air conditioner underperform and lights dim when a motor starts. It grows with distance, so a cable that is perfectly adequate at 10 metres can be undersized at 40.
Frequently asked questions
What is an acceptable voltage drop in house wiring?
3% is the recommended design limit for a domestic circuit, and 5% is generally treated as the maximum permitted from the supply point to the furthest outlet. Beyond that you get dim lighting, poor motor starting and, in pumps and compressors, overheating.
Why does a long cable run need a thicker wire?
Because voltage drop is proportional to length. The same current over four times the distance produces four times the drop, so a cable sized purely on current capacity can be well within its rating and still deliver unusable voltage at the far end.
What causes a borewell pump to burn out?
Frequently voltage drop over the cable down the borewell. Low voltage at the motor increases current draw and heat, which degrades the winding. Sizing the submersible cable for depth, not just for motor rating, is the single most effective preventative measure.
How do I reduce voltage drop?
Increase the cable size, shorten the run, or move the distribution point closer to the load. Increasing the size is usually the practical option — this calculator shows the smallest size that brings the run within 3%.
Does three phase have less voltage drop?
For the same power, yes. Three-phase current is lower for a given load and the line-to-line drop calculation carries a factor of about 0.866, so three-phase runs generally tolerate longer distances at the same cable size.
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