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Grid switch ratings enquiry

Farmboy
Had an interesting chat with a tech dept this afternoon after coming across some grid switches in a domestic kitchen.


Four grid switches (sharing a common backbox) are each fed via their own 16A cb's, and each feeds 1G sockets (for a cooker hood, fridge freezer, etc). Ignoring the cable sizes (the focus being on the grid switches), given the 13A plug fuses limits the loads in each cct, would you have the current rating of the grid switches equal to or higher than the 16A cb's (e.g. 20A), or lower (but equal to or higher than the socket rating e.g. 13A/14A)?


F
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    gkenyon:

    This leads to the question "Is it OK for a tumble dryer and a washing machine to be simultaneously plugged into a double socket-outlet?"


    Answers on a postcard to ...




    Ours have been for the past 20-odd years. ?


    Of course, it depends upon the machines. Ours total 5.15 kW = 22 A, which exceeds a double socket's rating of 20 A until diversity comes into play.

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    gkenyon:




    wallywombat:

    Bear in mind that a single socket could have a 2-way unfused 'cube' adaptor plugged into it, effectively turning it into a double socket, where 20A may flow (but never 26A, because that never happens, because Reasons),




    Being a little devilish ...


    Double socket-outlets to BS 1363-2 are now (to the current standards) rated at 13 A. Single socket-outlets are also rated 13 A.


    This leads to the question "Is it OK for a tumble dryer and a washing machine to be simultaneously plugged into a double socket-outlet?"


    Answers on a postcard to ...


     




    Best not to have a washing machine and a tumble drier on the same double 13 Amp. socket, as I have found recently when that situation caused the failure of the double socket due to a burn out of the switches.


    Z.

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    AJJewsbury:




    Presumably the single 13 Amp sockets are behind the appliances like the fridge freezer, or at high level above the extractor hood, so are very unlikely to be used for additional appliances. That is why there are conveniently positioned grid control switches. Therefore this is a non-issue. A 10 Amp grid switch will not catch fire or blow up if carrying 11 Amps in most cases. A 20 Amp grid switch will be fine for other appliances like washing machines or tumble driers etc. Overloading is very unlikely if the single 13 Amp sockets are inaccessible. Stop worrying needlessly.



    Ah, but you're only considering overload - what about fault currents?


      - Andy.

     




    Relating to the original post, I can not see how a cooker extraction hood or a fridge freezer can in any way cause a 20 Amp sustained current to flow through a grid switch for hours. The extractor will no doubt be fused at 3 or 5 Amps. The fridge freezer can not do so also. If the makers of the fridge freezer consider a 13 Amp fuse good enough to protect its flex then who am I to disagree?


    The other two appliances are unknown, they could be a hob and oven. Both can not by design each cause an overload of a 20A value under healthy or fault conditions. Also don't forget the R.C.D. protection.


    Anyway 20 Amp grid switches will cover that scenario.


    Z.


     

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    Zoomup:



    No it can't supply 20 Amps for hours. These are apparently single 13 Amp sockets for individual dedicated appliances like a cooker extractor hood and fridge freezer etc., so the loads are fixed. No overloading can occur.


    Z.



    I don't know that I would agree that no overloading can occur, though I would agree it is highly unlikely.  Generally a circuit overcurrent regions will be overload (from full load current up to about 2.5 times flc) and short circuit above that (and ok, there is a considerable overlap but I am trying to simplify here). Generally the overload is a mechanical problem such as a seized motor while the short circuit is an electrical problem such as insulation failure. Both of the examples you give (cooker extractor hood and fridge-freezer) have motors with bearings which can seize so an overload can occur. I would agree it is very unlikely as these devices normally fail for other reasons first.

    Alasdair

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    Some broken element faults cause overload. Luckily many of those are also earth faults so are detected by RCD these days, but not always overcurrent protective devices.
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    Chris Pearson:




    gkenyon:

    This leads to the question "Is it OK for a tumble dryer and a washing machine to be simultaneously plugged into a double socket-outlet?"


    Answers on a postcard to ...




    Ours have been for the past 20-odd years. ?


    Of course, it depends upon the machines. Ours total 5.15 kW = 22 A, which exceeds a double socket's rating of 20 A until diversity comes into play.


     




    20-odd years ago, BS 1363-2 socket-outlets, both double and single, used to be rated for (and marked) 20 A.


    The machines won't use full power all the time, only when heating elements are on, which is why a 20 A socket-outlet would likely be OK, but with 13 A rated double socket-outlets, I would strongly recommend against the use of 2 laundry and/or dishwashing appliances on the same double socket-outlet.

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    I agree with Graham here. The standard calls for a “per accessory” rating of 13A regardless of the number of outlets, so the maximum current that can be drawn from a double socket is 13A, the same as a single, and indeed a triple which should have a 13A fuse fitted to it.


    I am aware that certain manufacturers do rate their double sockets in excess of what is required by BS1362-2, however there is no need for them to do so, or guarantee that they will continue making sockets with the enhanced ratings. 


    Regards,


    Alan.
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    I agree with Graham here. The standard calls for a “per accessory” rating of 13A regardless of the number of outlets, so the maximum current that can be drawn from a double socket is 13A, the same as a single, and indeed a triple which should have a 13A fuse fitted to it.


    I am aware that certain manufacturers do rate their double sockets in excess of what is required by BS1362-2, however there is no need for them to do so, or guarantee that they will continue making sockets with the enhanced ratings. 


    Regards,


    Alan.
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    BS1363-2:2016+A1:2018


    Section 3: definitions


    "socket-outlet" accessory having a set of three socket-contacts designed to engage with the pins of a corresponding plug ...


    "multiple socket outlet" combination of two or more socket outlets


    Section 6: classification and rating


    6.1 The rated current of all socket-outlets shall be 13 A


    Section 16 specifies 14 A + 6 A for temperature testing.


    It must be that every BS1363 socket can safely supply 13 A indefinitely because that is what users are entitled to expect of them. Nowhere does it say that the total of a multiple socket-outlet is limited to 13 A. It is not expressly stated, but if a twin socket-outlet may safely supply 14 A + 6 A for at least 4 hours with a stable temperature, it may be inferred that it is safe to do so.
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    It must be that every BS1363 socket can safely supply 13 A indefinitely because that is what users are entitled to expect of them.




    Er, well the ones marked "EV" are supposed to be able to - which does rather beg the question of the others...

     




    It is not expressly stated, but if a twin socket-outlet may safely supply 14 A + 6 A for at least 4 hours with a stable temperature, it may be inferred that it is safe to do so.



    But equally it can be inferred that a continuous 13A+13A load (total 26A) isn't expected if they're only testing to 20A - and then for a limited time.


      - Andy.

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