Breaker Size Calculator for Dubai and the UAE

This is the single most important idea about breakers, and almost everybody gets it backwards.

People think the breaker protects the appliance. It does not. The appliance has its own protection inside it.

The breaker protects the wire in the wall. If something goes wrong and too much current flows, the wire will heat up. Given enough current for long enough, it heats up until the insulation fails and it can start a fire inside a wall where nobody can see it.

The breaker is set so it trips before the cable reaches that point. That is its entire job.

Which means a breaker is chosen for the cable it is protecting. You cannot put a larger breaker on a smaller cable, no matter what is plugged in at the end.

A circuit keeps tripping. Somebody swaps the breaker for a larger one. The tripping stops. Problem solved, apparently.

What has actually happened is that the safety device has been disabled.

The circuit was tripping because too much current was flowing for that cable. The cable has not changed. Now the breaker allows that current to keep flowing, and the cable gets hot, and nothing stops it.

This is one of the most common dangerous alterations found in existing properties, and it is invisible from outside a distribution board.

If a circuit trips regularly, the answer is to move some load off it, or to have a new circuit installed with cable to suit. Never to fit a larger breaker on the same wire.

Breakers come in types, marked B, C and sometimes D. The letter is about how quickly they react to a surge.

A type B trips fairly quickly on a sudden rise in current. That suits lighting and sockets, where a surge means a fault.

A type C tolerates a larger surge for a short moment before tripping. That suits motors, because a motor starting draws several times its running current for a second or two and there is nothing wrong.

Put a type B on an air conditioner and it may trip every time the compressor starts. Nothing is faulty. The breaker is simply the wrong type for the load.

Type D tolerates more again and is used for heavier industrial motor starting.

So when a circuit trips only at the moment something starts, and never while it runs, the curve is the first thing to check.

A breaker is not the only protection, and the two are often confused because they sit side by side.

The MCB, the breaker this tool sizes, protects against too much current. Overload and short circuit.

The RCD or ELCB protects people. It watches whether the current going out equals the current coming back. If some is leaking away, perhaps through a person or through moisture, it disconnects very quickly.

They do completely different jobs and neither replaces the other. A circuit can be perfectly protected against overload and still be dangerous without earth leakage protection.

In a UAE bathroom or kitchen, or anywhere outdoors, earth leakage protection matters a great deal, because water and electricity are close together.

If your RCD trips rather than a breaker, that is not an overload. Something is leaking to earth, and that needs finding rather than resetting.

Work through these in order before assuming anything is broken.