What is voltage drop?

The voltage lost pushing current through a cable. The longer the run and the smaller the cable, the less voltage arrives at the far end.

How much voltage drop is allowed?

Usually around three per cent for lighting and four per cent for general circuits, with a little more sometimes permitted for motors. The exact figures depend on the regulations for the building.

Why does my garden light flicker?

Often voltage drop over a long thin cable, made worse when something else switches on. The last light in a long chain is always the one that shows it first.

Why does my water pump hum and not start?

Starting a motor takes the most current, and that is when the voltage drop is worst. A pump at the end of a long run can have too little voltage to start even though it runs once going.

How do I reduce voltage drop?

Use a larger cable, shorten the run, or split the load across two circuits. A bigger cable is the usual answer and doubling the size roughly halves the drop.

Does voltage drop waste electricity?

Yes. The voltage lost in the cable turns into heat in the cable, which does nothing useful and is paid for on the bill.

Voltage Calculator

Supply voltage

Phases

Current in the cable

Length of the run

One way, from the board to the load.

Cable size

Allowed drop

Your answer

Voltage at the far end

221 V

A drop of 3.9 per cent, inside your 4 per cent limit.

Voltage lost: 8.96 V
Drop as a percentage: 3.9%
Allowed: 4%
Cable size: 2.5 mm2
Within limits: Yes

Copper conductors assumed. This is a planning figure, not a design. Cable selection also has to satisfy current capacity and protection.

Voltage Drop Calculator for Dubai and the UAE

This tool works out how much voltage is lost along a cable. It matters because a long run does not deliver the same voltage at the far end that it started with.

Every cable has resistance. Current flowing through resistance loses voltage, and the longer the cable and the smaller it is, the more is lost.

It is the reason a pump at the end of a villa, or a light at the end of a garden run, can behave badly while everything near the board is fine.

What voltage drop is

Electricity leaving your distribution board at 230 volts does not arrive at 230 volts. Some of it is used up pushing current through the cable itself.

The cause is resistance. Copper is a good conductor but it is not a perfect one, and a long thin wire has more resistance than a short thick one.

The current has to flow out and back, so the length that matters is double the distance you measured. That surprises people and it is why long runs go wrong faster than expected.

The result is that a load at the end of a long run sees less voltage than the board is supplying, and it may not have enough to work properly.

Why it matters more than people think

Low voltage at the far end causes specific problems, and they are often blamed on the equipment instead.

Motors run hot
A motor on low voltage draws more current to do the same work. More current means more heat, and heat is what kills motors.
Pumps struggle to start
Starting is when a motor needs the most. A pump at the end of a long run may hum instead of starting, and that is a voltage problem, not a pump problem.
Lights dim and flicker
Especially when something large switches on elsewhere. The drop gets worse as current rises.
Electronics behave oddly
Some equipment resets or reports faults on low voltage without ever saying that is the reason.
Heaters take longer
Less voltage means less power, so a heating element simply works more slowly and costs more to do the same job.

The limits and where they come from

Wiring rules set limits on how much voltage may be lost between the supply and the point of use.

Lighting is held tightest, usually around three per cent, because flicker and dimming are immediately visible.

General circuits are allowed a little more, around four per cent.

Motors are sometimes given five per cent, because they tolerate it better in normal running, though starting is still the difficult moment.

These are not arbitrary. Below those limits equipment behaves as designed. Above them, things start working badly in ways that get blamed on the equipment.

The exact figures that apply to an installation depend on the regulations in force for that building, which is one of several reasons the design belongs with a qualified electrician.

Where long runs happen in UAE properties

These are the places voltage drop actually shows up here.

Water pumps
Often at the far corner of a plot or in a plant room a long way from the board. And a motor, so starting matters.
Garden and boundary lighting
Long runs, small cable, and the last light in the chain is always the dimmest.
Gate motors and intercoms
At the end of the drive, which in a villa can be a very long way.
Roof plant
Water tanks, pumps and AC condensers on a roof are a long climb from a ground floor board.
Outbuildings and staff rooms
Separate structures fed from the main house, often on cable sized for the distance rather than for the load.
Villa extensions
A new room added years later and fed from an existing board at the other end of the house.

What to do when the drop is too high

There are only three answers, and one of them is not really an answer.

Use a bigger cable. This is the normal fix. Doubling the cross section roughly halves the drop, so going from 2.5 to 6 square millimetres makes a large difference.

Shorten the run. Sometimes a board or a sub board can be placed closer to the load, which fixes the problem at the source rather than compensating for it.

Reduce the current. Splitting a load across two circuits halves the current in each, which halves the drop in each.

The thing that is not an answer is ignoring it because the equipment still runs. Equipment running on low voltage is running hot, and it will fail earlier than it should.

Sizing cable for voltage drop rather than only for current is the difference between an installation that works and one that works for now.

Questions people ask

What is voltage drop?: The voltage lost pushing current through a cable. The longer the run and the smaller the cable, the less voltage arrives at the far end.
How much voltage drop is allowed?: Usually around three per cent for lighting and four per cent for general circuits, with a little more sometimes permitted for motors. The exact figures depend on the regulations for the building.
Why does my garden light flicker?: Often voltage drop over a long thin cable, made worse when something else switches on. The last light in a long chain is always the one that shows it first.
Why does my water pump hum and not start?: Starting a motor takes the most current, and that is when the voltage drop is worst. A pump at the end of a long run can have too little voltage to start even though it runs once going.
How do I reduce voltage drop?: Use a larger cable, shorten the run, or split the load across two circuits. A bigger cable is the usual answer and doubling the size roughly halves the drop.
Does voltage drop waste electricity?: Yes. The voltage lost in the cable turns into heat in the cable, which does nothing useful and is paid for on the bill.

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