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Overloaded fused spur, opinion please

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?
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  • Chris Pearson:
    perspicacious:

    So, with this in mind, would a 20 A JB attract any coding on an EICR if found on a 32 A RFC?


    OK, I have rummaged around and found an old BS 6220 JB. 2¼" diameter. It is marked, "NOMINAL CABLE 2.5 MM²" and "250 V 20A".


    BS 6220 says:

    5 Classification

    A junction box shall be classified according to:

    a) the number of terminals as declared by the manufacturer;

    b) the nominal conductor capacity of the terminals, as declared by the manufacturer, which shall be one of the capacities shown in column 1 of Table 2;

    c) the method of mounting (e.g. surface or flush).

    6 Marking

    6.1 All junction boxes shall be durably and legibly

    marked with the following:

    a) the number of this British Standard, i.e. BS 62201);

    b) the name or trade mark of the manufacturer or responsible vendor;

    c) the nominal conductor capacity of the terminals, i.e. “n mm2” or “n” ‘ where n is the conductor size in mm2;

    d) the rated voltage, e.g. “250 V”. Compliance shall be checked by inspection.


    So what we have is a (4-terminal) 2.5 mm² surface mounted JB. There is no current rating!


    The BS goes on to specify that at least 2 x the nominal conductor must be accommodated (else it wouldn't be a JB! ? ) and that the test current for the 2.5 mm² version is 30 A.


    So the answer, BAD, is "no".




    Why? The test current is greater than that for a BS 1363-2 socket-outlet? The voltage and current rating is that of conductors in a cable in a RFC?


    What makes it unsuitable for an RFC?


Reply
  • Chris Pearson:
    perspicacious:

    So, with this in mind, would a 20 A JB attract any coding on an EICR if found on a 32 A RFC?


    OK, I have rummaged around and found an old BS 6220 JB. 2¼" diameter. It is marked, "NOMINAL CABLE 2.5 MM²" and "250 V 20A".


    BS 6220 says:

    5 Classification

    A junction box shall be classified according to:

    a) the number of terminals as declared by the manufacturer;

    b) the nominal conductor capacity of the terminals, as declared by the manufacturer, which shall be one of the capacities shown in column 1 of Table 2;

    c) the method of mounting (e.g. surface or flush).

    6 Marking

    6.1 All junction boxes shall be durably and legibly

    marked with the following:

    a) the number of this British Standard, i.e. BS 62201);

    b) the name or trade mark of the manufacturer or responsible vendor;

    c) the nominal conductor capacity of the terminals, i.e. “n mm2” or “n” ‘ where n is the conductor size in mm2;

    d) the rated voltage, e.g. “250 V”. Compliance shall be checked by inspection.


    So what we have is a (4-terminal) 2.5 mm² surface mounted JB. There is no current rating!


    The BS goes on to specify that at least 2 x the nominal conductor must be accommodated (else it wouldn't be a JB! ? ) and that the test current for the 2.5 mm² version is 30 A.


    So the answer, BAD, is "no".




    Why? The test current is greater than that for a BS 1363-2 socket-outlet? The voltage and current rating is that of conductors in a cable in a RFC?


    What makes it unsuitable for an RFC?


Children
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