19-05-2017, 08:02 PM
(14-05-2017, 04:15 PM)colly0410 Wrote: Remember reading somewhere that ring mains can only be safely used with fused plugs otherwise a faulty short circuited gubbins would get the full 30 amps, wereas with a 13 or 3 amps fused plug the max current would be err 13 or 3 amps in theory..
I used to think on similar lines but that isn't right.
The 30A fuse/32A breaker in the consumer unit protects the ring.
The plug fuse protects the cable connected to it so, if you are using 0.5mm² flex rated at 3A, you shouldn't fit a fuse larger tha 3A.
0.75mm² is rated at 6A and 1mm² at 10A. You should be using 1.25mm² or heavier flexible cable if a 13A fuse is fitted.
As for the equipment at the far end of the flex, it is the manufacturers responsibility to provide protection for that. Hence a wallwart doesn't have a replaceable fuse, although it is essentially a 13A plug because there is no flex to protect. There should, however, be internal protection* inside the (sealed) case. It isn't replaceable because you can't get inside!
* Whether there is or not in a lot of cheap stuff imported from China is, of course, another matter ...
