25 year old condo...never had HWH.  There is an open slot in my box for a new circuit.  3500 watt heater.  Would like to know if a 20amp breaker, and a 20amp safety switch would be OK?  And what guage wire?  Been getting several different answers...3500/220=15.909..which would indicate a 16 amp breaker, but I recall the switches are 20 or 30..so would it be best to have them match.

Thanks!

2.5mm² cable and a 20A breaker would be adequate.

 

If you're running new cable. Installing 4mm² cable and a 30A breaker would allow you to go to 6kW when the 3.5kW isn't hot enough.

 

You could use an RCBO instead of a simple MCB in the box, no need for an additional "safety breaker".

 

Post an image of your box with the lid off for more directed advice.

the main is 45...then a 16, a 16, and a 20.....then the open slot.  Would be nice to not do the safety switch..but is that possible with an ungrounded system?

and the AC is on the 20 with no safety switch, and is still working good and efficiently at age 15.

 

Let me know if you want me to remove the cover for another photo..

The majority of water heaters I looked at recently had a built in earth leakage device...its easy to tell without taking the cover off if one is installed because there will be a button labeled "test" and some mechanism to reset the safety switch...however I still took the lid off in the shop to check and also see if the heating element was housed in a copper or plastic jacket...plastic being the norm now on the lower priced units I looked at,sales assistant said plastic ones more liable to split/leak...? ? still I went with a plastic one as it was a "good price"

My old Joven (on the left) had no built in earth leakage detection and developed a leak at the flow sensor switch which was in exactly the correct spot to come in contact with 220AC and then run down the water input hose !...I had installed an separate 15ma earth leakage breaker,but luckily spotted the leak before inadvertently testing it out for real.

Despite it trying to make a run for it (motion blur) that looks like a Schneider / Square-D box, you should be able to get 10 or 30mA RCBOs to fit so no need for an extra safety breaker.

 

You really need to arrange an earth, certainly run 3 core from your heater back to the box.

 

As far as earthing is concerned, do you have metal water pipes, good for a functional earth (don't use the fire pipes), maybe there's access to the building steel.

 

Whilst many, if not all, modern heaters having built-in RCDs they won't protect from contact with the incoming supply, I like to see RCD/RCBO in the box too.  

strictly PVC plumbing.  my ceiling is all metal under the poured concrete, with a drop down ceiling, which is likely aluminum.

 

As far as plastic vs. metal tanks .they were pushing that at Powerbuy, but I see sediment causing trouble on either.  My installer five years ago suggested letting it run cool for a few seconds before shutting the water off..that seemed to make sense, because notice if you turn it off hot, and then back on, it will make sizzling noises.  But, I wonder why the safety switch is so common here, even when the unit has the test?