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Do I need to hardwire?

Discussion in 'Electrics UK' started by M1AK, 22 Oct 2016.

  1. M1AK

    M1AK

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    Hi all,

    I bought a new integrated microwave, which spec wise, initially appeared to be equivalent to our existing integrated microwave. Both are 900w however the existing one has a total power figure of 2500w and the new one is 3350w.

    The new 3350w integrated microwave comes with a rather chunky cable but no plug at the end of it. I am assuming that it is so it is hardwired?

    Unfortunately where it is fitted there is no hard wiring capability and therefore I consulted a electrician - who actually said that if i'm just using it for basic microwave capabilities then I can just wire it to a normal 13amp fused plug and it will be fully protected, when in a normal plug socket.

    Is this perfectly ok or should this appliance be strictly hardwired only. The manual of the item does not specifically say whether it needs to be hardwired - which i thought it would. Sometimes there are tags on wires that say hardwire only, but there is nothing here.

    I only intend on using the microwave and not the grill or convection feature as have a grill/oven for that.
     
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  3. winston1

    winston1

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    Well 3350w at 240 v is a shade under 14 amps. It's all very well saying you won't be using the grill or convection feature, at some stage someone will, say if your oven broke.
    Also will this "rather chunky" cable fit in a 13amp plug?

    Two choices

    1. Change the microwave oven for one without the features you won't use.
    2. Get it hardwired on it's own circuit back to your CU.
     
  4. JohnW2

    JohnW2

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    As far as I am aware, diversity can be invoked for a combi-microwave, just as for any other cooking appliance.

    On that basis, one could consider the (after diversity) current of a 3350W appliance at 240V as being about 11.2A, hence OK on a 13A plug (as you say, if the cable will fit in!).

    Kind Regards, John
     
  5. slippyr4

    slippyr4

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    Is it really wise to apply diversity? In the case of a combi oven there would frequently be a time when the element and the magnetron are both powered.
     
  6. JohnW2

    JohnW2

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    Diversity applies over time as well as 'place'. An element would not be on continuously when it was 'switched on' - it would cycle on and off (per thermostat), so that the average over a period of time would be appreciably less than the total 'everything drawing power' figure.

    It's not really any different from a hob - it's not uncommon for most/all of the hotplates to be 'on' simultaneously, but the time-averaged load would be much less than the total of all 'on' hotplates, which is why the concept of diversity is reasonable, and allowed.

    Kind Regards, John
     
  7. slippyr4

    slippyr4

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    So how long might a BS1363 fuse last at 14.5A ? Indefinitely?
     
  8. JohnW2

    JohnW2

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    Yes, indefinitely. If you look at previous discussions here (and illustrations of the performance curve), it appears that it requires something like 21/22A continuously for a 13A BS1363 fuse to blow ever.

    Even a 13A Type B MCB (if you could find one) would be required never to operate with less than 14.69A continuous (13 x 1.13) and could take up to an hour to operate at 18.85A continuous (13 x 1.45). At 14.5A continuous, it could take a good few hours to operate. If it weren't for these facts, the application of diversity would frequently result in fuses blowing or MCBs/RCBOs tripping - which is a very rare occurrence (you'll see a lot of discussion about 'Christmas Day' - but, even then, any problems are very uncommon).

    Kind Regards, John
     
  9. John D v2.0

    John D v2.0

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    The other thing you should really take account of is the 13a plug can heat up quite a lot under its rated load and damage the socket too.
    Check the manufacturer's instructions as you are supposed to follow them regardless of the general standards that apply.
    Personally I'd be tempted to use a fcu even though it would then be a pain to move it for cleaning.
     
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  11. M1AK

    M1AK

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    Thanks for the replies - the reason why I know for sure that we won't use the convection or grill is that we only ever use it to heat up things quickly using the microwave. I already have a big oven and a mini oven, so don't need a third one.

    The ratings are as follows:

    Output: 900w
    Grill: 1750w
    Input: 1650w
    Convection: 1750w
    Max Power 3350w

    240v @50Hz
    Frequency: 2450MHz.

    No where does the manufacterer recommend to hardwire or 13a plug - so it isn't clear from the manufacterers point of view.

    I picked this all singing all dancing unit for next to nothing and thats why i'm trying to make it work as just a replacement to a basic microwave, but only if I can 'SAFELY' get away with wiring it up to a 13a plug. The wiring is a bit chunky but think it will fit a plug perfectly fine.
     
  12. EFLImpudence

    EFLImpudence

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    If it didn't come with a plug fitted, you should hard-wire it.
     
  13. JohnW2

    JohnW2

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    Provided only that the cable can be satisfactorily/safely connected to the plug, then so long as you only use the microwave facility, there would obviously be no problem with connecting it via a plug.

    As you have seen, some people would be less happy if the other (grill/convection) facilities were ever used (at same time as microwave) - but, as I have said, I personally don't see that, in practice, there would ever be a problem using a 13A plug, even then. There are plenty of ovens out there which have a 'max power' of around 3300W which come with a fitted 13A plug.
    I wish that the manufacturers could be clearer in their specs - since it is far from clear (at least, to me!) exactly what all that means - although I presume that one can safely assume that the maximum power consumption is 3350W! Does the 'Input' perhaps refer to the microwave ('Output' 900W) and is it perhaps not possible to use both grill and convection 'separately' (they could well essentially be the same thing) - but, even then 1650 + 1750 is not exactly 3350!

    So, in summary, I would personally be very happy to use a 13A plug if only the microwave was ever to be used, and also happy if that were not the case. In the latter case, the very worst thing which could happen is that the plug could get hot during prolonged use - but I'm sure you would notice that before it became 'a danger' (use your nose :) ).

    Kind Regards, John
     
  14. EFLImpudence

    EFLImpudence

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    I really don't think that that is the way to do things.
     
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  15. JohnW2

    JohnW2

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    As a principle, I agree, but it extremely unlikley to happen in practice. I was merely alerting the OP of the 'very worst that could happen', even though I don't believe it would be any more likely than with many other 'high powered' appliances supplied via 13A plugs ....

    I would (again 'theoretically') be far far more concerned about a tumble dryer supplied via a 13A plug, but how often do you see them hard wired?

    Kind Regards, John
     
  16. John D v2.0

    John D v2.0

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    Just for fun, if you did hard wire it, since it's over 2kw you should then provide its own circuit from the CU. Even if people did hard wire their dryer, they wouldn't be likely to do that!
    I think in summary to the op, it's not strictly compliant, you wouldn't leave it like that in someone else's house, but if you understand the setup it's unlikely to cause any harm.
     
  17. JohnW2

    JohnW2

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    As will be apparent, I certainly personally agree with the latter, but, as I've said, I also believe that it would probably be "strictly compliant" unless one was arguing that, for some reason, it was not appropriate to apply diversity to this particular 'cooking appliance'.

    Would you also regard it as not being 'strictly compliant' if one ran, say, a 10kW ('max power') cooker off a 32A circuit?

    Kind Regards, John
     
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