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Cable Size Calculator

A

Work it out from the watts with the watt to amp calculator.

m

One way, from board to load.

A hot or crowded route means the cable carries less safely.

Your answer

Cable size to use

2.5 mm2

Current capacity decides this one. The run is short enough that voltage drop is not the limit.

Needed for current
2.5 mm2
Needed for voltage drop
2.5 mm2
Current
20 A
Run length
30 m
Derating applied
80%

A planning figure only. Cable selection is work for a qualified electrician against the regulations in force for that building.

Cable Size Calculator for Dubai and the UAE

This tool suggests a cable size. It checks two things at once: whether the cable can carry the current without overheating, and whether the voltage still arrives at the other end.

Most simple charts only check the first one. That is why long runs sized from a chart often work badly, because the cable is big enough to be safe and too small to be useful.

It also allows for temperature, which matters here. A cable in a UAE ceiling void is already hot before any current flows.

Cable has to pass two tests

The first test is current. Can the cable carry the load without getting hot enough to damage its insulation. This is the safety test, and it is what a simple chart answers.

The second test is voltage drop. Does enough voltage still arrive at the far end for the equipment to work properly. This is the performance test.

A short run is nearly always decided by the first. A long run is nearly always decided by the second.

That is the trap. A cable can be perfectly safe and still deliver a supply too weak to start a pump. Nothing is overheating, nothing trips, and the pump just hums.

So the right size is whichever of the two tests demands more. This tool works both out and gives you the larger answer.

Why UAE heat changes the numbers

Cable current ratings are published for a reference ambient temperature. That reference is a mild climate.

A cable can only carry current because it can shed the heat that current creates. If the air around it is already hot, it sheds less, so it can carry less.

A ceiling void in a UAE building in summer is a genuinely hot place. A cable sitting in it starts warm and has less margin before it reaches its limit.

The same applies to cables bunched together in a tray or a conduit. Each one heats its neighbours, and the whole group derates.

This is why a cable sized from a chart written for a temperate country can be undersized here even though the arithmetic was done correctly. The chart assumed conditions this building does not have.

What decides the derating

These are the conditions that reduce what a cable can safely carry.

  • Ambient temperature

    The biggest factor here. A hot roof void, a plant room or an outdoor route in the sun all reduce capacity noticeably.

  • Grouping

    Several cables together in a conduit or tray heat each other. The more there are, the less each can carry.

  • Thermal insulation

    A cable surrounded by insulation cannot shed heat at all in that section. This is one of the largest reductions there is.

  • Installation method

    Clipped to a wall in open air is best. Buried in a wall, in conduit, or in a sealed trunking is progressively worse.

  • Buried in the ground

    Different rules again, and it depends on how deep and what the soil is like.

Common cable sizes and what they are used for

Typical usage in UAE homes. Always confirm against the actual circuit and route.

  • 1.5 mm2

    Lighting circuits. Small current, and usually short runs within a floor.

  • 2.5 mm2

    Socket circuits. The most common cable in a home, and the one most often stretched too far on a long run.

  • 4 and 6 mm2

    Water heaters, air conditioning units, ovens, and socket circuits on long runs.

  • 10 and 16 mm2

    Sub mains, larger air conditioning, feeds to an outbuilding or a separate board.

  • 25 mm2 and above

    Main incomers and large three phase equipment. This is where the supply arrangement matters as much as the cable.

Why oversizing a little is often right

Cable is one of the few things in a building that is genuinely hard to change later. It is buried in walls and ceilings, and replacing it means opening them up.

Everything else on a circuit can be swapped. Breakers, sockets, fittings and equipment are all accessible. The cable is not.

So where a run is long, where the load might grow, or where the route is hot, going one size up is usually money well spent. It costs a little more once and it removes a whole class of future problem.

It also reduces the voltage drop and the heat, which means slightly less energy wasted in the cable for as long as the building stands.

What oversizing does not do is replace a proper design. A larger cable on the wrong protection, or with the wrong installation method, is still wrong.

Questions people ask

How do I choose a cable size?

Check two things: whether it can carry the current safely, and whether the voltage still arrives at the far end. Take whichever answer is larger.

What cable size for a 20 amp circuit?

On a short run, 2.5 square millimetres is usual. On a long run the voltage drop test can push it to 4 or 6, even though the current alone would not.

Why does cable capacity drop in the UAE?

Because ratings assume a cooler ambient temperature. A cable in a hot ceiling void starts warm, so it can shed less heat and carry less current safely.

Does cable length affect the size I need?

A great deal. On long runs voltage drop, not current, decides the size. A cable that is perfectly safe can still deliver too little voltage to start a motor.

Is a bigger cable always safe?

Larger cable is generally fine and often sensible, but it does not replace a proper design. The protection, the installation method and the terminations all have to suit it too.

Can I do this work myself?

Cable sizing and installation is work for a qualified electrician, and in this country the installation has to comply with the regulations that apply. Use this tool to understand and to ask better questions.

Need the job done

We do this work across Dubai

Use the numbers above to plan, then let us quote the real thing.

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