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Overloaded fused spur, opinion please

Foffer
I was an industrial electrician and have now come across a domestic wiring issue where nothing appeared wrong with the installation.  Those with more experience will have probably have come across this many times.


The kitchen is supplied by a 2.5mm T&E ring fed from a B32 circuit breaker.  On this ring there is a 13A fused switched spur above the worktop feeding a double socket underneath via 2.5 T&E.  There is a washing machine and a dishwasher plugged into this double socket.  Every so often, I assume when both appliances are heating at the same time, the 13A fuse in the spur blows.  The cable supplying this double socket is in the wall so the current-carrying capacity appears to be 18.5A so this was probably being overloaded as well.


I understand that in the regs diversity covers some aspects of this situation, but this specific situation must occur often surely?  The switched spur gives the ability to switch off the appliance easily without having to pull it out in order to reach the switch, so is surely desirable?


In this case I have installed a second switched fused spur feeding a single socket and converted the other to a single.


Is this a common problem in kitchens?
  • 0
    The trouble is it is not ALL there in Appendix 15 which is only informative and does not show everything that is possible.
  • 0
    geoffsd:

    The trouble is it is not ALL there in Appendix 15 which is only informative and does not show everything that is possible.


    Everything I said is there ... to put every possible permutation of a ring final circuit in any diagram, or even a set of requirements, is of course not possible.


  • 0
    Geoff, you have put your finger on the problems we have, and that is the fundamentals are not properly taught or understood. Graham is right, there are any number of possible permutations of circuits. The limits are clearly set out in BS7671 (not the OSG, which is only a set of possibles). If the limits are understood, it is clear that anything else is allowed. A huge increase in education is required, and that is the challenge.
  • 0
    gkenyon:



    BS 5733 if memory serves for the 20 A DP switch.

     




    The Low Voltage Directive 2006/95/EC

    BS EN 60669-1:1999 + A1:2002 + A2:2008

    Modified ISO 22196


    Therein lies the “problem” with 20 amp double pole switches being used in kitchens to switch sockets and appliances, that and the fact that a lot of the “installation managers” working for the big shed kitchen companies like MFI attended 16th Edition Wiring Regulations courses and were awarded the C&G, so they could “inspect” the electrical work completed by kitchen fitters.


    These “electrical inspectors” would point out the requirements of 537 Isolation and switching and in particular Table 537.4 which states that the 20 amp switches don’t provide isolation, unlike 13 amp SFCU.


    That has set the standard for kitchen fitters and kitchen installations for the last twenty years with an insistence that SFCU should be used above work surfaces to control appliances and inaccessible sockets, because you can take the fuse out of them.


    Generally that’s fine, until someone uses a SFCU to control a double socket.


     Andy B.


  • 0
    Sparkingchip:
    gkenyon:



    BS 5733 if memory serves for the 20 A DP switch.

     




    The Low Voltage Directive 2006/95/EC

    BS EN 60669-1:1999 + A1:2002 + A2:2008

    Modified ISO 22196


    Therein lies the “problem” with 20 amp double pole switches being used in kitchens to switch sockets and appliances, that snow the fact that a lot of the “installation managers” working for the big shed kitchen companies like MFI attended 16th Edition Wiring Regulations courses and were awarded the C&G, so they could “inspect” the electrical work completed by kitchen fitters.


    These “electrical inspectors” would point out the requirements of 537 Isolation and switching and in particular Table 537.4 which states that the 20 amp switches don’t provide isolation, unlike 13 amp SFCU.


    That has set the standard for kitchen fitters and kitchen installations for the last twenty years with an insistence that SFCU should be used above work surfaces to control appliances and inaccessible sockets, because you can take the fuse out of them.


    Generally that’s fine, until someone uses a SFCU to control a double socket.


     Andy B.




    The switch is OK to remove power and provide control. The appliance plug and socket-outlet can provide isolation for maintenance.


    If BS EN 60669-1 is good enough for a cooker switch, which requires a "proper" means of isolation such as the circuit protective device, then it's good enough for an under-counter appliance connected via plug and socket-outlet.


    Or the world has gone mad.


    The user will not remove the fuse and lock off the appliance overnight, so the switch on the FCU does nothing different. The purpose of providing the above counter switch - removing power for fire safety reasons and emergency switching - is still achieved by providing a switch to BS EN 60669-1 instead of an SFCU ...


  • 0
    I don't imagine that many of them passed the then 2391 exam, so what did they get? Presumably a one-day "you do it like this" course and a bit of paper.
  • 0
    You know that and I know that, but the kitchen “installation managers” that went on the 16th Edition courses to become “qualified” would not have it, so they set the standard for how things are being done.


    One asked me if I had the “Wiring Regulations” certificate. I replied I did and that I also had the 2360 parts one and two, I&T and 2400. He said “It doesn’t matter about those others, so long as you have the Wiring Regulations certificate”.


    Twenty years ago with a box of SFCUs and a Wiring Regulations certificate you were the go to guy for kitchen electrical work  ?
  • 0
    As always I am concerned about two flat plates clamping a round conductor (sorry I keep harping on about it).

    I think the point about terminal ampacity is that any number of conductors bunched together in a terminal has many points of contact so providing it is mechanically secure then good ho in my opinionas you are not relying solely in the current carrying capacity of the terminal itself.

    That`s what I liked about the old wylex 604 etc - a round terminal hole and two screws, a sight sphere on the pointy end to cause a slight anchor by dimpling the conductor and of course two such screws increased anchoring and area of contact.


    I know a bloke, he says he has a degree in electrical engineering (I have no reason to doubt him).

    He claims that he was taught that doubling (or twisting) conductors to increase point of contact is not only wrong but "ruf" in his opinion.

    He disagrees with me and his wife`s brother (an electrician) about that.

    To my way of thinking, if in an ideal world, your conductor size and shape matches the terminal size and shape then current transfer between conductors is good.

    I did not like the look of his one strand of 1.0mm2 conductor in an ashley JB20A  on his security lighting (tungsten halogen) and that`s why I mentioned doubling to him and got his ruf comment.

    I am not aware of anyone else agreeing with him
  • 0
    This is what happens in the real world, you get a group of people in a certain trade or business that set a way of doing things, that’s not always technically correct or logical, then twenty years later when you question someone who has done things the same way for twenty years as to why they do it that way they either don’t know or can’t remember why, but just know that’s the way it’s done.


    Kitchen fitters and electricians have got into the habit of using SFCU above work surfaces in kitchens to control inaccessible sockets rather than 20 amp switches, because “that’s the way it done “.


    It all goes back to the kitchen installation managers having done a Wiring Regulations short course twenty years ago and Table 537.4 in BS7671 saying that 20 amp switches don’t provide isolation.


    Just to complicate it more they would also point out that table says plug and sockets don’t provide emergency switching, so even if the socket was accessible you still needed the SFCU, as the SFCU fulfils all three requirements of isolation, emergency switching and functional switching.


    Old habits die hard!
  • 0
    Sparkingchip:


    Just to complicate it more they would also point out that table says plug and sockets don’t provide emergency switching, so even if the socket was accessible you still needed the SFCU, as the SFCU fulfils all three requirements of isolation, emergency switching and functional switching.


    Interesting that a switched socket-outlet can't be used for emergency switching


    Regardless of BS 7671 and BS 1363-2 say, people do use them like that ... so the requirements in BS 7671 don't match the real world. An ordinary person wouldn't have any awareness of the difference, and simply switch off at the socket-outlet (if switched) and unplug a portable appliance if they saw smoke coming out of it.


    Anyway, no-one said that a single device has to be provided to meet all of the requirements.


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