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Two high-power appliances on a single 40A RCD

Former Community Member
Former Community Member
I have an electric shower installed on a 40A RCD, in a room adjacent to my kitchen. The shower is only used in an emergency - i.e. when our gas boiler is unable to provide hot water to our main bathroom. I would like to take a spur from this 40A connection to use for a new double oven, which is rated at 32A. Can anyone advise on a safe and legal way to do this, ensuring that only one of the two appliances can be connected at any one time?
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    cfcman:

    I have an electric shower installed on a 40A RCD, in a room adjacent to my kitchen. The shower is only used in an emergency - i.e. when our gas boiler is unable to provide hot water to our main bathroom. I would like to take a spur from this 40A connection to use for a new double oven, which is rated at 32A. Can anyone advise on a safe and legal way to do this, ensuring that only one of the two appliances can be connected at any one time?







    Presumably you have a 40 Amp M.C.B. A changeover switch will allow only one of the loads to be used at a time.


    Here is an example of a big 100 Amp version. I am sure that small versions are available say rated at 45 Amps.

    https://www.tlc-direct.co.uk/Products/CGCS1004P.html?source=adwords&ad_position=&ad_id=315107931576&placement=&kw=&network=u&matchtype=&ad_type=&product_id=CGCS1004P&product_partition_id=576185600782&campaign=shopping&version=finalurl_v3&gclid=EAIaIQobChMIja3cz7Gh5gIVQbDtCh1-owZSEAQYASABEgKq1vD_BwE


    Z.

  • Former Community Member
    0 Former Community Member
    Yes I have a 40A circuit breaker in the consumer unit. Presumably an MCB changeover switch is something which sits in the consumer unit? I would actually need a switch downstream of that - i.e. in the kitchen/bathroom - as I would want to switch the supply between two appliances on the same circuit?
  • 0

    cfcman:

    Yes I have a 40A circuit breaker in the consumer unit. Presumably an MCB changeover switch is something which sits in the consumer unit? I would actually need a switch downstream of that - i.e. in the kitchen/bathroom - as I would want to switch the supply between two appliances on the same circuit?




    A 40 Amp M.C.B. is a miniature circuit breaker. You referred to a 40 Amp R.C.D. I assumed that you meant an M.C.B.


    The changeover switch will not be located in the consumer unit, it is too big. It will be installed downstream of the origin of the circuit.


    Z.

  • 0
    It might be worth use of a "shower priority unit" these are primarily intended for connection to two electric showers so as to prevent simultaneous use. I have used these units for other large loads.

    Get one that gives priority to shower number one. Connect the cooker to the "shower one" terminals and the shower to the "shower two" terminals. The cooker can then be used as normal, but the shower will be isolated when the cooker is in use. The shower may be used as normal provided that the cooker is not in use.


    Or a manual changeover switch as previously suggested. These are widely sold and primarily intended to connect an installation to either mains supply or to a generator, but never both. They can also be used to connect a single supply to either of two loads, but never to both loads.
  • Former Community Member
    0 Former Community Member
    Yes it's an MK Electric 7937S which is an MCB/Residual Current Device I believe? OK so I would have the MCB changeover switch installed in the kitchen as a replacement for the existing on/off wall switch for the supply to the electric shower?

    I was told by a kitchen fitter that he was not legally able to put two high power devices on the same circuit, so presumably this would address that issue?
  • 0
    What is wrong with simultaneous use, it will trip the MCB at some point, strangely that is what the MCB is for!!!! Belt and braces efforts at design are not required. Kitchen fitter does not have a clue! I wonder which regulation that is? Answers on a postcard to the Screwfix forum.
  • Former Community Member
    0 Former Community Member
    TBH I would be quite happy with simultaneous use, as the shower is not used from one year to the next (and only when our boiler breaks down), but the kitchen fitter told me that connecting the oven and the shower on the same circuit would be illegal for him to do.

    ???
  • 0

    cfcman:

    TBH I would be quite happy with simultaneous use, as the shower is not used from one year to the next (and only when our boiler breaks down), but the kitchen fitter told me that connecting the oven and the shower on the same circuit would be illegal for him to do.

    ???




    The important thing is that the cable is the appropriate size for the circuit breaker. That means that the cable cannot be overloaded - if you connect too much simultaneously, as DZ mentions above, the circuit breaker will trip. That's the worst that can happen, so if you are not going to use the shower whilst cooking dinner, just connect the new cooker to the existing circuit.


    It may be that your kitchen fitter is a member of a competent persons scheme which limits him to kitchen work. Clearly the shower is not kitchen work.

  • 0
    It is not illegal. It may be out of his comfort zone, which is fair enough, but then he should be honest about it. Be aware that wiring in bathroom zones (i.e within 60cm of the bath or shower cubicle ) requires notification under part P, and he may not  be keen to get involved in that, or he may be worried that he gets called back if something trips.

    If it was my house, and I know who will use it, I'd parallel them up and have a variation on the single line working token system for Victorian trains, - perhaps when the bar of soap is in the kitchen it is OK to cook, when someone takes it into the shower it isn't.  Or a label on the shower for visitors - "check is anyone cooking ? Do not overload the trip !" Actually cooking is not as thirsty as folk often imagine - once initial heating is over the thermostat pings on and off and the average current is quite low. It is a cold start that is the problem.
  • Former Community Member
    0 Former Community Member
    Ah OK so when he said he wasn't "legally" able to do it what he maybe should have mentioned that this was due to a limitation of his professional certification, rather than being an absolute legal constraint. So basically I was talking to the wrong type of tradesperson?

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