I was looking at some loads recently and at Crossys site and the FAQ above.

The following shows the cables sizes for the appropriate circuit breaker;

1.5 mm² cable - 15 amp maximum circuit breaker.
2.5 mm² cable - 20 amp maximum circuit breaker.
4 mm² cable - 25 amp maximum circuit breaker.
6 mm² cable - 32 amp maximum circuit breaker.
10 mm² cable - 40 amp maximum circuit breaker.

thanks to Crossy site click here

When I add up gadgets and stuff on partcular circuits, it is much easier to do that in watts, how to convert watts at 220V to amps ?

For our purposes:-

Watts = Volts x Amps

Transposing for Amps.

Amps = Watts / Volts = Watts / 220

There are also rules of thumb to determine 'diversity' as it's unlikely that all the kit on a circuit will be operating together. So you could actually have more load than the circuit can handle without opening the breaker (think kettle, toaster, grill, microwave).

So, for example, a 3.5kW shower = 3500 Watts / 220 = 15.9 Amps, so 2.5mm² cable and a 20A breaker would be adequate.

For these approximations we can discount Power Factor.

Thanks crossy

Doncaster cables one of the uks leading suppliers have a very good cable sizing calculator on there website.

Volts multiplied by amps = watts

or

Watts divided by volts = amps

Volts in Thailand being 220

Look at the wattage of your appliance, divide it by 220. The answer is the minimum amperage of the breaker you will need but it's better to add around 15% to cover a surge.

Doncaster cables one of the uks leading suppliers have a very good cable sizing calculator on there website.

Indeed they do, here:-

http://www.doncastercables.com/technical-help/

The only negative is that it restricts the volt-drop to the UK requirements of 3% or 5%

The calculator here is limited to a maximum cable of 16mm² but you can juggle the parameters http://www.crossy.co.uk/wiring/VoltageDrop.htm