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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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  • Yes David.


    So, how do I know increased resistance can tip things over the edge?


    As you'll be aware, it isn't unknown for the wiring in a detached garage to be spurred off a kitchen ring, using [cynical moment coming up] 2.5 T&E clipped to a fence.


    The number of failures of this type, where replacement capacitor lasts only a short time, was observed to happen far more frequently with tumble dryers used in this situation, or also off a "4-way" with other appliances. And this is compared to very few observed failures in garages supplied using SWA in a more conventional [compliant] manner, from their own way on the primary CU.


    I'm guessing a combination of primary voltage drop on the kitchen ring, plus additional through the FCU to the garage etc, is the real issue, and similar for running the tumble dryer off a 4-way extension in a kitchen.


    This won't be too different to an FCU feeding a socket outlet for a tumble dryer in the same kitchen - hence my initial comment on this. If you want to provide isolation "above the unit" for under-counter appliances, use a 20 A DP switch to supply the under-counter socket-outlet ...  and not an SFCU.
Reply
  • Yes David.


    So, how do I know increased resistance can tip things over the edge?


    As you'll be aware, it isn't unknown for the wiring in a detached garage to be spurred off a kitchen ring, using [cynical moment coming up] 2.5 T&E clipped to a fence.


    The number of failures of this type, where replacement capacitor lasts only a short time, was observed to happen far more frequently with tumble dryers used in this situation, or also off a "4-way" with other appliances. And this is compared to very few observed failures in garages supplied using SWA in a more conventional [compliant] manner, from their own way on the primary CU.


    I'm guessing a combination of primary voltage drop on the kitchen ring, plus additional through the FCU to the garage etc, is the real issue, and similar for running the tumble dryer off a 4-way extension in a kitchen.


    This won't be too different to an FCU feeding a socket outlet for a tumble dryer in the same kitchen - hence my initial comment on this. If you want to provide isolation "above the unit" for under-counter appliances, use a 20 A DP switch to supply the under-counter socket-outlet ...  and not an SFCU.
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