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Diversity of two single ovens?

Discussion in 'Electrics UK' started by eveares, 2 Dec 2015.

  1. eveares

    eveares

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    So was doing a little paper excessive to keep by brain active. If you had:

    A) A single oven rated 3.5Kw (i.e. Steam oven)
    and
    B) A second single oven rated at 3.0Kw (i.e. Microwave combi oven)

    That would give you a current rating of 11.56A for the first oven and 10.91A for the second oven once diversity had been taken into account right? (Domestic household and no socket)

    (10A + 30% remaining current + 5A for socket outlet if applicable) for each appliance.

    Now the catch is each oven's manual stipulates that it must only be fed from a OCPD of a maximum rating of 20A.

    Now if I have done the diversity calcs correct, the current with the diversity taken into account would be 22.48A - Roughly 2.5A over the maximum OCPD that can be used, meaning the ovens would effectively have to be on their own circuit from the CU.

    Have I got this all correct?

    Regards: Elliott
     
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  3. ban-all-sheds

    ban-all-sheds

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    Not 15.12A?
     
  4. ericmark

    ericmark

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    In the real world diversity depends on what is being used. Take a standard oven and on switch on it takes maximum power for may be 10 minuets but after that time the load will be intermittent and very short. The microwave oven is very different cook baked spuds and 15 minutes could be followed with another 15 minutes at full load. Although it is a microwave combo oven the oven load and microwave load may be very different. So in the real world we have to guessterminate on likely hood of the load tripping a 20A MCB. Likely that will be very low so we use a 20A MCB what ever result we get to calculations.

    That is the real catch. It is what I expected, but I have looked at the spec for many ovens expecting to see a maximum size of supply, but all those over 3 kW and under 3 kW a simple FCU will do so only interested in over 3 kW I have not found one where the manufacturer stipulates anything under 32A which seems to be the standard size for most cookers.

    Have you actually found an oven over 3 kW where the manufacturers says 20A? I think not?
     
  5. cjard

    cjard

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    (((3.5 x4.17)-10)*0.3)+10 = 11.38
    (((3x4.17)-10)*0.3)+10=10.75
    ((((3+3.5)*4.17)-10)*0.3)+10=15.13

    BAS, Did you sum the loads first? (Not saying it's wrong, just curious)
     
    Last edited: 2 Dec 2015
  6. OwainDIYer

    OwainDIYer

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    Not quite. You can provide a shared 32A circuit from the CU, and provide individual 20A OCPD to each oven locally.
     
  7. JohnW2

    JohnW2

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    He did, and that's the normal way of doing it. If you think about it, the more separate cooking appliances one has on a circuit, the more does the concept of diversity apply to the total load.

    Kind Regards, John
     
  8. ban-all-sheds

    ban-all-sheds

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    I have a money-saving tip for you - just throw the potatoes in the bin before wasting electricity like that...
     
  9. ban-all-sheds

    ban-all-sheds

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    Which means installing a CU just for the ovens.
     
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  11. eveares

    eveares

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    Yes, Page 44: https://drive.google.com/file/d/0BxexGKdHyIBmVXNHbnBPangySW8/view?usp=sharing It's the oven I have and is rated 3.5Kw by the sticker on the front.

    The Combi Microwave oven says the same thing on page 40 and is rated at 3.0Kw: https://drive.google.com/file/d/0BxexGKdHyIBmTE1DeTJGSHI2cEU/view?usp=sharing


    I got the diversity of the two appliances individually (10A + 30% Remainder) and then simply added the figures together. (11.56A + 10.91A = 22.47A)


    Of course that's possible, but not ideal nor practical. I was talking about if both were fed from one OCPD.
     
  12. JohnW2

    JohnW2

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    Of course, if you want to obey the MIs, since the after-diversity current (of the two appliances combined) is well under 20A, you could theoretically run both off a circuit with a 20A OPD, thereby keeping both MIs happy.

    Kind Regards, John
     
  13. eveares

    eveares

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    So you would treat the two appliances as a combined load, and thus apply the diversity to the total combined load and not each appliance individually?
     
  14. JohnW2

    JohnW2

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    As I said before, yes. As I said, the more appliances there are, the more does the concept of diversity (applied to the total combined load) become justifiable.

    Running your ~28A theoretical total cooking load off a 20A circuit is actually much more conservative than, say, running a "15kW" (65A) mega-range-cooker off a 32A circuit/OPD, although that is perfectly 'allowable' (~26.5A after diversity).

    Kind Regards,
     
  15. ban-all-sheds

    ban-all-sheds

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    What if it were sold as a single item - a twin oven in the same housing, with one set of terminals to connect?
     
  16. Astra99

    Astra99

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    Compare the following:
    Standalone all-electric cooker (four hobs, single oven and grill)
    Electric hob with separate single oven (which includes a grill)
    Electric hob with separate double oven (including grills)

    I contend that all the above (in a domestic environment) would be viewed identically; diversity would be calculated on the sum of the loads. Thus, wherein lies the problem with the OP's setup?
     
  17. JohnW2

    JohnW2

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    Exactly - as was implied (and then clarified) early on.
    As I've said, there is no problem - provided that, if he wants to adhere to the MIs, the circuit has a 20A MCB (which is fine for a total after-diversity load of around 15A).

    KInd Regards, John
     
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