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Replacement Single Oven - 13A or 16A

Discussion in 'Electrics UK' started by imroberts, 11 May 2019.

  1. imroberts

    imroberts

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    I'm looking for a replacement single oven. Ideally I want to use an existing 13A FCU rather than install a new 16A circuit.

    Ideally I'd like to buy the Bosch HBG674BS1B however the supply is detailed as 16A. I understand 16A is a standard circuit across Europe and the oven doesn't necessarily draw this amount of current
    https://www.bosch-home.co.uk/product-list/cooking-baking/ovens/built-in-ovens/HBG674BS1B

    The older model, the HBG673BS1B is rated at 13A and can still be purchased however at a substantially higher price
    https://www.bosch-home.co.uk/product-list/exclusive/HBG673BS1B

    I can't find any detailed spec which details the actual consumption of the oven so I know it's maximum current draw, however all the specifications I can find for the two ovens, including the energy consumption per cycle all appear to be identical.

    How can I determine whether the HBG674BS1B would be fine connected to a 13A FCU or do I need to buy the older model?
     
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  3. JohnW2

    JohnW2

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    The relevant part of the spec for the HBG674BS1B is here ...
    upload_2019-5-11_11-16-31.png

    3.6 kW at 230V equates to 15.65A. Applying the concept of diversity (which takes into account that the full 'maximum load' will not be drawn continuously for appreciable periods of time), that can be regarded as 11.7A (the first 10A, plus 30% of the rest). It should therefore be fine on a 13A supply (13A plug or FCU).

    Kind Regards, John
     
  4. jj4091

    jj4091

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    Is that really applicable with an oven, it is going to be on full load for quite a while whilst it is coming up to temp.. Personally I thought that diversity could only be applied to cookers where all the rings will not be on at the same time. But I would not argue the point if that is a reg.
     
  5. JohnW2

    JohnW2

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    The 'standard' diversity guidelines (not 'regulations') apply equally to all cooking appliances, not just hobs.

    Even with an oven switched on from cold, it will not remain on full power for all that long initially (how long does your oven take to 'heat up'?) and then will cycle on/off. What matters (and what diversity takes into account) is the average load/current over an appreciable period of time (say 30 minutes or so), and that will always be well under 16A for an oven which presents a maximum load of 16A - and that's what the standard diversity calculation takes into account.

    Kind Regards, John
     
  6. imroberts

    imroberts

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    So I should be fine connecting the newer HBG674BS1B to a 13A FCU by the sounds of it?

    The thing that really confuses me is if you look at the older HBG673BS1B and the HBG673BB1B which are identical ovens except the BS1B is silver and the BB1B is black, however the BS1B is listed at 2.99kW total connected load and the BB1B at 3.60kW which makes me think they're probably all 2.99kW in reality anyway.
     
  7. AndyPRK

    AndyPRK

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    Why is the old oven in a 13a fcu anyway?

    Can you post some pics of the cooker isolator switch ?

    And what value Mcb B?? Turns the oven off at the consumer unit ?
     
  8. JohnW2

    JohnW2

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    What do you mean by "the cooker isolator switch"? It sounds as if an FCU was being used for that purpose

    Kind Regards, John
     
  9. ban-all-sheds

    ban-all-sheds

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    I think that jj has a point that that might not be applicable to a single element item, like an oven. As per the other thread, those guidelines are donkey's years old, and when written a domestic electric cooker had an oven and rings. You could argue that a kettle, or a toaster, don't present their full load over "an appreciable period of time", but nobody does.


    Even on the self-cleaning program?
     
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  11. JohnW2

    JohnW2

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    As I said, that would be my opinion.
    That does seem odd - but who knows what the truth may be!

    Kind Regards, John
     
  12. AndyPRK

    AndyPRK

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    I was unsure WHY it had an fcu

    Pics can tell a lot.

    If the oven had a grill or second oven diversity could be considered.
     
  13. JohnW2

    JohnW2

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    I obviously agree that the strength of the argument for application of diversity reduces somewhat when there is only one element, but there is still 'diversity over time' and I don't think that, even when switched on from cold, the element(s) will draw 'full power' for an extended period of time - and they will certainly cycle on and off once they have reached operating temp. In any event, I think that, in the 'starting from cold' situation, 'single element' is not particularly relevant since, even if there are multiple elements involved, if they are all switched on simultaneously from cold, they will all draw 'full power' until each of the heated areas get up to operating temp.
    I also wonder how likely it is that a 3.6 kW oven does have a single element?
    If I ever needed to, I would present that argument since, in normal use, the average current draw of such items over, say, half an hour would be very low. However, since such items are always going to have a maximum draw under 13A, I can't see why I would ever need to consider diversity in relation to them
    I have no idea. It's well over 30 years since I had an electric cooker of any sort, let alone a 'self-cleaning' one.

    However, by raising these theoretical arguments, you are at risk of putting doubts in the OP's mind. Do you really think that there would be a problem in connecting the 3.6 kW oven (which may actually be 2.99 kW!) with a 13A plug or FCU?

    Kind Regards, John
     
  14. AndyPRK

    AndyPRK

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    I would like to think any circuit on 2.5mm cable should be capable of supplying at least 20A.

    A pain a 13A fcu has been fitted. Would be nice to understand why.

    If there is a good reason ?
     
  15. JohnW2

    JohnW2

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    Fair enough. I had imagined that the OP's previous oven probably 'required' 13A protection, and that an FCU has been preferred over a 13A plug/socket - but I'm sure the OP can clarify.
    They sometimes can, but if it's just a pic of an FCU, it well not help us much. It seems pretty likely that the OP has a gas hob.
    As I've just written, I somewhat suspect that a 3.6 kW oven might well have more than one element.

    However, as I've also just written, I think this 'single element' argument is a bit of a red herring, anyway, since if everything is switched on simultaneously from cold, all elements will initially draw 'full power', simultaneously, until they reach operating temperature.

    I would also add that it's really only the fuse (in the FCU or plug) that people are fussing about ** - there is no way that this cooker is going to be supplied from a circuit with a cable that cannot happily carry well over 16A, and extremely unlikely that the OPD of the circuit would be rated less than 16A (which, in practice, is only seen with lighting circuits!).

    ** ... and I would add that, as often discussed, it takes something like 22A (continuous) to blow a 13A BS1362 fuse.

    Kind Regards, John
     
  16. JohnW2

    JohnW2

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    Exactly.
    As I said, it's possible that the previous oven said that it should be protected by a 13A fuse, and the person installing it preferred to use an FCU than a plug/socket.

    Kind Regards, John
     
  17. AndyPRK

    AndyPRK

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    Someone following MI. No. Very unlikely!

    Did the old one come fitted with a plug?

    Don’t particularly want a fuse that will just get hot and end up with poor contacts
     
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