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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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    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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  • 0

    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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