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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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    Chris Pearson:

    BS1363-2:2016+A1:2018


    <snip>

    Section 6: classification and rating


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

    <snip>

     




    That's the bit that the manufacturers use to determine the rating, which is marked on the back of each double socket-outlet, e.g.:

    18a2fd876f5b97478217a2ca2ba699c4-huge-img_20190628_125528133.jpg



    I'm sure many older socket-outlets were marked "20 A", but this stopped quite a while back.



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



    That's a "type test", not an "in-use test".



    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.



    I disagree, the type test is only carried out on samples, for a 1-off occasion. Just because a sample socket-outlet lasts a single exposure of 4 hours to 20 A, doesn't mean production socket-outlets are capable of repeated use at the "overstress" current !



    So, regardless of how you personally interpret the snippets you posted, the manufacturer has stated the rating, and we shouldn't exceed that.


    Whether a user would know, as you say, is another issue, but I guess the manufacturer would class it as misuse if it were to cause a problem.

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    Chris Pearson:

    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.




    Am I reading this differently from everyone else? If a 'multiple socket outlet' is a combination of two or more socket outlets and the rated current of all socket-outlets shall be 13A, surely this means a multiple socket outlet with two socket outlets must be rated at 13A + 13A, or 26A for the unit. Or is this wrong?

    Alasdair

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    The ratings on double socket-outlets say it all.


    In fact, you could interpret the test requirements as they used to be stated, that the double socket-outlet is tested at the same stress level (20 A total) as a single socket-outlet, as these stress tests haven't changed in a very long time.


    The only difference between the two, is that for the single socket-outlet, the load of 14 A is drawn from the socket-outlet, the 6 A load is placed on another set of conductors at the rear.


    The double socket-outlet has, as since combined units appeared, never been assumed to take two 13 A loads in the stress test (otherwise that test would have to be 2 x 14 A loads, one in each outlet)?
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    Am I reading this differently from everyone else? If a 'multiple socket outlet' is a combination of two or more socket outlets and the rated current of all socket-outlets shall be 13A, surely this means a multiple socket outlet with two socket outlets must be rated at 13A + 13A, or 26A for the unit. Or is this wrong?



    If that's the wording from the standard it does seem a little ambiguous. " rated current of all socket-outlets shall be 13A" could be read to mean that the current rating of all outlets taken together as a group shall be 13A, or that each outlet individually shall be capable of carrying 13A but says nothing about the total rating (e.g. you could take the full 13A from either the left hand outlet, or the right hand one, but not necessarily both together).


    Consider too that the ring circuit design assumes that unfused spurs can't draw more than 20A from a dual socket - so there does seem to be a long term understanding that 13A+13A isn't what's expected.


       - Andy.
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    While on the ratings of sockets, has anyone found a supplier of the "EV rated" ones, and what test current are they rated at ? Or are they mythical?

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    The socket-outlets marked "/EV" are tested and rated in the same way, but some tests (breaking capacity, clause 17, and normal operation, clause 18) are carried out at a power factor of 0.6 +0/-0.05 and the number of cycles for the normal operation test, clause 18, has a different number of cycles.
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    Overloading of 13 Amp sockets can cause this sort of problem, although in his case the heating of the plug pin was probably caused by a loose terminal screw and the heat was transferred to the socket. Also sockets can be burned if overloaded by having too many appliances plugged into them and overloading them.

    https://www.youtube.com/watch?v=b99n3tesnqY


    Z.
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    I've seen similar situations where the plug and socket-outlet are not overloaded, say appliances running at about 2 kW, but bad connections in the plug (loose terminal screw, or, with moulded plug, similar cases such as broken strands on crimps or brazing)
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    AJJewsbury:




    Am I reading this differently from everyone else? If a 'multiple socket outlet' is a combination of two or more socket outlets and the rated current of all socket-outlets shall be 13A, surely this means a multiple socket outlet with two socket outlets must be rated at 13A + 13A, or 26A for the unit. Or is this wrong?



    ... e.g. you could take the full 13A from either the left hand outlet, or the right hand one, but not necessarily both together ...

    It would be absurd if one could take the full 13 A from one side of a twin socket and nothing from the other - there would be no point in having a twin socket.
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    gkenyon:

    I've seen similar situations where the plug and socket-outlet are not overloaded, say appliances running at about 2 kW, but bad connections in the plug (loose terminal screw, or, with moulded plug, similar cases such as broken strands on crimps or brazing)




    In my box of souvenirs, I have a (moulded) 13 A plug which was fitted to a 3 kW heater and whose sleeving around the live pins has melted. I don't think that it was overloaded as such, but that it was not pushed all the way into the socket-outlet. Some arcing may have occurred.

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