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Electrician's Advice Wanted

Discussion in 'Lounge' started by Arquebus, Apr 1, 2019.

  1. I'm OK with most domestic wiring; but this problem has got me confused.

    I need to add a 5.5kw instantaneous electric water heater (under sink type) in one area of my house for hand washing etc.

    There is an 8kw Titan instantaneous shower in the same place, but this is supplied by a single heavy cable (can't recall the size at the moment but IIRC max capacity is around 10kw) via an RCD at the mains distribution board.

    There is also an isolator switch outside the shower as one would expect.

    There is no chance of getting another cable to the same location as the shower to feed the water heater as it would have to run through a very long roof space with limited access.

    So what I think I need is a 3 position switch fitted after the shower isolater which is 'On' for water heater; 'Off'; and 'On' for the shower.

    This so either unit can be used subject to the switch position; but not both at the same time because of the risk of overloading the cable.

    If the idea isn't daft, what sort of switch do I need and what amperage rating?

    The switch would be fitted in a studwork wall as is the isolater.

    The plumbing side is simple.

    Any assistance advice would be appreciated.

    Thanks, AL.
     
  2. You need a changeover switch rated at 40 Amps or above. If you look at RS Components website they should have something suitable but most will be surface mounted not flush fitting.
     
    #2 NoGutsNoGlory, Apr 1, 2019
    Last edited: Apr 1, 2019
  3. Thanks.....I assume you mean a rotary type switch?

    I thought the bulk at the back of them could be accommodated behind a panel??

    AL
     
  4. The switch itself could be removed from the enclosure and fitted into a custom made panel.
     
  5. Cheers, I guess the panel lid could be cut down to a more respectable size and screwed to the plasterboard with some decent fixings.

    But you don't think the idea is daft?
     
  6. You can't cut it down, as the other side is bigger and needs to form the enclosure to protect the cables and act as a cable clamp for cable security.
     
  7. Not at all it will be safe as long as installed correctly.
    Not at all. It will be safe as long as it's installed correctly. Both heaters will still require local isolation switches.
     
    • Agree Agree x 1
  8. Q. What size is the fuse on the board, as this defines the switch....
    40A is big and is more unusual for a domestic.... 32A perhaps?
    Loads of 32A and 20A change overs around.... nice and neat.... but that fuse defines it.
     
  9. The problem with giving advice on the net is we aren't there to see the bigger picture as to what other regulations/advice may come into effect.
    A short video or even some pictures could help.
     
    • Agree Agree x 1
  10. The shower is 8kw so 32A would be under rated.
     
  11. After the meter, the same size cables as the incoming tails, run to a chocolate box, then that serves the distribution board; and two separate trips; one of which is a 40A RCCB 30mA trip for the shower supply cable. IIRC it is 6mm twin and earth.

    I checked out to see if that size cable would be adequate for one appliance; but not two; hence what I am suggesting is a way round it.

    But I will have to make sure on the cable size just in case it is 4mm, although I am sure when I had to do some jiggery around with positions for the new distribution panel; chocolate box; trips and tails, it was the same as the cooker cables which are 6mm.

    I will get some pics later on.

    Thanks, AL
     
  12. OK - so the single isolator switch before the changeover switch isn't sufficient?

    To my thinking it would isolate any power to the switch and therefore neither appliance can be used.
     
  13. Pics: The isolator switch is about 25 metres from the RCCB and I ain't crawling horizontally on my belly through that length of roof space and back to get another cable in. (I hate wasps, flies and insulation).
    ISO.jpg DIST.jpg RCCB.jpg
     
  14. Ok... my concern is now that you really need a 10mm cable to do that much current over 25m....
     
    • Agree Agree x 1
  15. Is there any overload protection on the shower circuit or the karlgester circuit?
     
  16. The 40Amp RCCB with earth leakage trip is pictured for the shower... can't read the treatment plant.... cable looks very small?!!
     
  17. Been looking at it all this morning.

    Just to sort the Klargester question, the motor is only 50 watt with a full load current of 0.51 amps. The RCCB is 80Amp, but there is another RCCB next to the Klargester as well. That end has an earth stake - quite a distance away from the house. Inside the white box with the running light, the white cable connects to armoured cable.

    I have probably made an error on the size of the shower dedicated supply cable. Without removing the RCCB and checking the core sizes, and not being able to spot any text on the bit that shows; I looked at the two cooker cables again, because I know for certain they are the same size as the shower cable. They are definitely 10mm (and they all measure 16.5mm x 9.5mm).

    Bear in mind the majority of the wiring here is 25 years old (red/black twin and earth). I have been here 20 years and I haven't looked at the system for at least 19 years when it was all tested OK after I had fitted the new distribution unit because it had the old wire 4 fuse box and very little in the way of separate circuits.

    Hope that clears some of it up.

    AL
     
  18. AirCon, sorry, I can see the RCCB and the adjacent RCD, which provide the earth leakage protection, but not overload protection? They aren’t RCBOs which would provide both? Unless I’m missing something.
     
    • Agree Agree x 1
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