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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?
Parents
  • Graham, I think that is wrong and misleading. The only thing which affects the slip in an induction motor is the LOAD, not the supply voltage. A fuse that lost 1V at 13A wouldn't last long, 13W is quite sufficient to blow a 100A BS88 fuse quite quickly. If the motor is electronically controlled, it is probably not an induction motor and so there is effectively no slip. This is not a mechanism of induction motor failure, mechanical overload is due to increased motor current and therefore winding resistance loss, not due to excessive rotor (squirrel cage) current which is entirely caused by the level of "slip". A normal 13A fuse dissipates around 500mW- 1W under normal maximum current, which is less than 500 mV drop. Note that supply voltage variation between 208 and 253 V (phase to neutral) does not cause failure!
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  • Graham, I think that is wrong and misleading. The only thing which affects the slip in an induction motor is the LOAD, not the supply voltage. A fuse that lost 1V at 13A wouldn't last long, 13W is quite sufficient to blow a 100A BS88 fuse quite quickly. If the motor is electronically controlled, it is probably not an induction motor and so there is effectively no slip. This is not a mechanism of induction motor failure, mechanical overload is due to increased motor current and therefore winding resistance loss, not due to excessive rotor (squirrel cage) current which is entirely caused by the level of "slip". A normal 13A fuse dissipates around 500mW- 1W under normal maximum current, which is less than 500 mV drop. Note that supply voltage variation between 208 and 253 V (phase to neutral) does not cause failure!
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