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Shower and undersink water heater.
Former Community Member
I have a property that has 6mm mains swa cable coming into the consumer unit via an RCD isolation switch. The home has a 7.2kw electric shower and I wanted to add a 7kw under sink water heater. So as to prevent overheating of the main cable and tripping of the main incoming fuse which is just 40 amps, could I put a 32 Amp 3 Pole Change Over Switch ahead of the two six mm cable wires which would be serving the shower and the water heater. Therefore negating overloading the main wire coming into the home by allowing only one of the appliances to be used at a time.
You could indeed have a simple change-over switch (a double pole or even single pole would do) - nothing electrically wrong with that. Might be a bit inconvenient for the user though - about to step into the shower and find the switch is in the wrong position...
The other approach is to automatically disconnect the water heater when the shower is in use - there are various load shedding relays available to do that, or they can come ready assembled as a "priority" unit - e.g. https://www.meteorelectrical.com/catalogsearch/result/?q=priority (just one example).
Yes, Andy thanks for the info. I posted a similar post on another electrical forum and got the same answer. Another similar solution could be to use a 40 amp NC contactor with a wire running back from the load contacts of the shower isolation switch to the consumer unit and into the contactor? When the shower is on this would open the contacts of the contactor, which would be wired to the mcb for the water heater. Does this sound reasonable and passable for an EICR?
The EICR needs to be done by someone who can understand it, and part of that is the instructions and description information provided with the installation, but yes, no reason why an EICR would be a problem if it is done well. If the signal wiring going back from the shower to the contactor is only protected by the 40A breaker then it should probably be fused down to avoid raised eyebrows.
Ok, many thanks for all the advice. Will have to give this some more thought as I was hoping this might be an easier solution to replacing an old gas water heater which is past it's shelf life.
