2 water heaters can't work together

[jobin]

I have 60 amps total coming into my flat. One water heater takes a 20 amp breaker, then a 10 amp on/off switch outside the bathroom. In addition, I want to install a continuous water heater in the garage which is 29 amps. Obviously I cannot operate both simultaneously. So I want to install a ‘changeover’ (single pole double throw) switch just outside the CPU. What size, amperage, switch would be best? Also of course I would need to up the size of the CPU breaker to 30 amp. Some of this question is whether ‘too big’ is any danger or problem. If I operate the smaller water heater, 6 amps, on the 30 amp breaker, will that be any problem I don’t understand ? I see that now the breaker is 3x the size of the unit so maybe this Q is immaterial. Comments welcome

 

[RedHerring2]

The rating of switches, breakers, etc is the maximum current rating. There's no problem running lower currents through these units.

 

[Paul_C]

One water heater takes a 20 amp breaker, then a 10 amp on/off switch outside the bathroom.

What is the actual rating of the water heater itself?

 

[jobin]

The water heater now in place is 3000W. Which i estimated to be = 6 amps.

 

[Paul_C]

More like 13A at 230-240V, so for a start the 10A switch is underrated and should be changed.

 

[Monkeh]

The water heater now in place is 3000W. Which i estimated to be = 6 amps.

You don't estimate, you calculate. It's a dreadfully simple calculation, and if you can't do it you should put the screwdriver down and leave it to someone who can.

 

[jobin]

Thanks for the comments both up/down. I will make some adjustments to the situation.