Hi to all, any electricians out there? I have and existing tankless 4500W hot water system in the shower, I would like to know if I upgrade to a 6500W system, what size cable and breaker do I need to supply power to the 6500W system? The current 4500W shower has 2.5 mm cable with a 16 amp breaker. I was thinking maybe 4 mm wiring and 20 amp breaker, not sure? Any info would be appreciated, cheers.

Your 6500W heater is going to pull around 30A so a minimum of 4mm² cable and a 32A breaker.

 

Personally, if I was going to have to pull a new cable I'd stick in 6mm² with a 40A breaker and have done with it.

 

Next stop, 8kW heater!

 

36 minutes ago, Crossy said:

Next stop, 8kW heater!

It is only a few days a year (at least normally - last two years almost none but we may pay the price this year) and with a good heater you can lower the water flow enough to be comfortable (in Bangkok) with the normal 3.5k units (although you may want to turn off the bathroom fan until after the shower).

 

For good T shirts highly recommend this firm - very good price and quality and fast shipment.  Not wife beater weather.

https://shopee.co.th/product/36428537/527434789

  

I replace the master bath shower heater with this... Installed it in the attic just above the shower (Was also thinking of just putting it on the wall just outside the shower but thought it would not look nice)... In the attic works great as is is usually hot up there... The unit only draws 2,000 watts with a regular plug so no special wiring needed...

https://www.homepro.co.th/p/1016377

Here is a selection 

https://www.homepro.co.th/c/PLU0502