Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 114 replies
  • Subscribers 32 subscribers
  • Views 11969 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

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?
  • 0
    Wow, this discussion is getting a bit heated isnt it?

    well my tenpernorth.

    our traditional diversity for a "cooker" has prettymuch stood the test of time.

    sensible use of the standard clac is allowed providing that we consider if there are any underlying reasons not to use it.

    i have, over time, considered a few where oven and hob are on different circuits but together present no more diversified load than a full blown traditional cooker.if someone wants to put those two units on ond ciruit i would not usuallyhave a problem with that unless cir umstances dictate otherwise.

    however this combinstion we are discussing is different, two possibly unrelated activities.that is the problem.

    the OP suggests that their particular usage pattern would not present a problem and that could be correct in intention and indeed in pratice.

    however, the stiuation does leave to open to abuse, either by the OP or others.

    I have no problem with a sensible change over/power sharing arrangement that prevents both appliances running at the same time if separate circuits would be too inconvenient to install for some reason. Not the most elegant of circuits but hey ho doable.

    what i do feel uncomfortable about is a circuit that invites overloads big or small.

    yes we do allow overloads up to 13% as normal and a circuit must not trip. Cable calcs etc give us that headroom.

    at 45% overload a circuit must trip , altjough it could take hours to trip. 

    a masive overload would (should) trip quite quickly.

    i would not like to run a circuit that encourages a breaker to run on  its curve for any meaningfull duration.

    i feel that this circuit encourages the possibility of such overloads even rarely and is best avoided.

    so my vote is either two circuits or a switchover such as a shower priority type set up.

    by the same token i would not like a ring (or radial) with a 16A mcb in circuit running an oven in most instances, again separate circuits or a low wattage plug in typd if you must.
  • 0

    4000 Watts divided by 240 volts = 16.7 amps, if you divide be 230 it comes out at 17 .4 amps.




    It doesn't work like that.

    If you are going to use 230V for design then it will be 16A - surprise.

    At 250V, it will be 17.4A so perhaps one should allow for that just in case.




    If you look at a selection of double ovens you will find the manufacturers rating stated as required for the fuse or MCB doesn’t tally with the actual ratings they give for the ovens.



    There aren't that many fuse/MCB ratings to choose from and no reason why a manufacturer should specify one anyway.

    Most (single) oven instructions state that a 16A supply is required (even if the actual amperage is lower) because that is the rating of circuits they have in Europe.


    Presumably a double oven states 32A for the same reason - i.e. two circuits except in Britain.

    Even that is only 16.6A after applying diversity.

  • 0
    The calculation based on the requirements of BS7671


    Rating on plate 4.0 kW


    So 17.4 amps at 230 volts.


    Therefore 10 amps plus 30% of 7.4 amps gives an assumed current demand of 12.3 amps


    So is everyone satisfied with having a double pole B16 MCB in a metal enclosure connecting the oven to a 32 amp socket ring circuit, rather than increasing the potential load on the shower circuit by over 12 amps?


     Andy Betteridge 


  • Former Community Member
    0 Former Community Member

    Sparkingchip:

    As I suspected the manufacturer has overstated the circuit requirement.


    That oven will be quite safe on a 2.5 mm circuit with a 20 amp MCB or RCBO. That doesn’t particularly help if you don’t have such a circuit.


    It is almost on the point of being able to be connected to a socket ring circuit with a 16 amp MCB at the point it is connected to that circuit.


    4000 Watts divided by 240 volts = 16.7 amps, if you divide be 230 it comes out at 17 .4 amps.


    If you look at a selection of double ovens you will find the manufacturers rating stated as required for the fuse or MCB doesn’t tally with the actual ratings they give for the ovens.


    To be perfectly honest in my home I would prefer to see it connected to a socket ring circuit using a 16 amp MCB than connected to the shower circuit, after all the existing oven has been wired that way for many years.


    Though I would still recommend a new circuit is installed.

     




    That's interesting. The sockets in the kitchen are on a 32A circuit breaker in the consumer unit. A new circuit is really not feasible for me, mainly on grounds of cost. So are you saying that a separate 16 or 20 amp MCB could be installed in the kitchen - e.g. where the socket for the existing oven is located? (it's a double socket which is also used for a toaster).

  • 0
    1d4fb6705916e847acfe175c9462a539-huge-20191208_231437.jpg

  • 0
    As I suspected the manufacturer has overstated the circuit requirement.


    That oven will be quite safe on a 2.5 mm circuit with a 20 amp MCB or RCBO. That doesn’t particularly help if you don’t have such a circuit.


    It is almost on the point of being able to be connected to a socket ring circuit with a 16 amp MCB at the point it is connected to that circuit.


    4000 Watts divided by 240 volts = 16.7 amps, if you divide be 230 it comes out at 17 .4 amps.


    If you look at a selection of double ovens you will find the manufacturers rating stated as required for the fuse or MCB doesn’t tally with the actual ratings they give for the ovens.


    To be perfectly honest in my home I would prefer to see it connected to a socket ring circuit using a 16 amp MCB than connected to the shower circuit, after all the existing oven has been wired that way for many years.


    Though I would still recommend a new circuit is installed.


    Andy Betteridge
  • Former Community Member
    0 Former Community Member

    Sparkingchip:

    Is the existing oven gas or electric?


    Is the existing oven supplied by a plug from socket circuit or goes it have its own circuit, if it foes have its own circuit what size is the cable and the protective device got it in the consumer unit?


    Exactly what oven have you bought?


     Andy Betteridge 


     




    The existing oven is electric - plugged into a 13 amp socket on the kitchen circuit. The new oven is a Belling BI702FPCT:
    https://www.currys.co.uk/gbuk/household-appliances/cooking/ovens/belling-bi702fpct-electric-built-under-double-smart-oven-black-10190536-pdt.html

  • 0
    Is the existing oven gas or electric?


    Is the existing oven supplied by a plug from socket circuit or goes it have its own circuit, if it foes have its own circuit what size is the cable and the protective device got it in the consumer unit?


    Exactly what oven have you bought?


     Andy Betteridge 


  • 0

    But that is kind of the point, is it not?  


    Is that a deflection or a cloud (sic)?



    Its a female aardvark


    Again, what diversity can you apply to a shower?


    Regards


    BOD



    You can apply it to a final circuit with more than one load, if appropriate. The shower is the only thing on the circuit, so that is the final circuit current demand. So my banana....diversity is not a consideration. The design current Ib is the current demand of the only point of use. But before it is suggested that by adding another point of use, diversity could then be applied to this shower and the connected load and, by engineers magic, Ib remains the same, that can only be so in a controlled environment. A domestic house is not that, as, no disrespect to the OP, that environment can be subjected to misuse. So a changeover system is required
  • Former Community Member
    0 Former Community Member

    Chris Pearson:



    Thank you for the photograph. I feel obliged to make a couple of observations (with all due respect):


    (1) It is not a large property, so a shower for emergency use seems a little lacking in credibility;


    (2) There isn't a lot of room for a double oven. I also note what appears to be a stack of at least three microwaves. ?


     




    Oh dear it seems that a picture is not always worth a thousand words :0(

    I'm not entirely sure how your inferences were derived regarding the size of the property, or the "credibility" of a shower for emergency use - I'm not entirely sure what was meant by that?....

    But to clarify:


    • The property is a 3-storey townhouse. I'm not sure what your definition of "large" is, but my guess is that the average UK homeowner would not describe it as "small"

    • The photo shows a small corner of a reasonably-sized kitchen (approximately 12 square metres)

    • There is plenty of space for a double oven to replace the existing single oven (I don't see much value in another photo to illustrate this particular point)

    • The property has three bathrooms - one on each floor. The photo shows the kitchen on the middle floor. The adjoining bathroom is used as a WC, but also has the electric shower in question, which was installed 10 years ago, specifically as a backup in the event of a boiler failure. The associated power supply was installed at the same time.

    • Those are indeed three microwave ovens - well spotted.


    I'm not entirely sure how/whether any of this is relevant, but I guess more information is usually better than less....

Community Rules & Guidelines