What do you mean by a competent person? It seems to me that you are going to do something without understanding the potential of such an action. It is unlikely that your shed is on a ring final circuit as you state.
I'm very grateful for your concern as to my levels of competence. Most touching.
Oh I see, I get concerned when I see simplistic approaches such as changing the mcb for a higher rating. I incorrectly assumed that you were not aware that this would be notifiable work as required by Part P.
I much prefer the HSE's "Suitability Qualified and Experienced" over the BR's "Competent" for this very reason...
So would your 13 and 15 amp plugs be protected by a 16 amp breaker, and the 16 amp plug be protected by a 20 amp breaker?
The ring main should be consigned into the history books, and there is no usually! Each circuit from a distribution board should be designed to handle the required load and cable chosen based on current, volt drop and method of instalation. 2.5mm radial on a 20 amp device or a 4.0mm radial on a 32 amp device. The protective device is then selected to ensure that circuit wiring is protected under fault conditions. Yes I have seen 16 amp sockets wired into a ring main but this is a no no as there is no protection. Also you cannot just change the type of protective device. A 16 amp type B will need 3 to 5 times the working current to trip (48 to 80 amps). A 16 amp type C requires 5 to 10 times the working current to trip(80 to 160 amps). Is the loop impedance of that circuit low enough to allow the increased fault current required, it could well have been marginal before the change. Also remember that the total loop impedance is not just that of the wiring within your shed, it is the whole circuit back to the local sub, before modern testers it was refered to as external impedance Zo. Providing the fault is L to N then earthing is less of an issue but L to the conductive parts of a machine and then you realise how important the means of earthing can become. Examples here are people using armoured cable, incorrectly glanded or placing to much reliance on the armour for the CPC, run the earth as a core within the cable and that can make life easier. With large industrial supplies we used to run seperate CPC's along with the armoured cables, ie a 95mm cpc with a 185mm 4 core.
Hi Steve
My TS has a 2.2Kw motor and runs from a 13 amp plug, the same as my bandsaw but there is a lot more to supplying a load than just amps. The length of a cable run introduces a volt drop which will effect the current you can pull, your supply is at the end of an extension lead and protected by a 13 amp fuse which will more than likely not be capable of running your loads. There is a solution but not when you have to cross a public space, can you not move the saw closer to your house when it is needed, I know it is weather dependant but there are others in a similiar position. Not knowing what you are cutting, but let's assume sheet goods then rather than the table saw have you thought about a tracksaw! With a couple of tressles it will give you a Portable solution for less cost.
I'll echo Spectric's comments about cable run lengths. As someone who spends a disproportionate amount of his working life out on construction sites I have experienced loads of issues with extension cables which were too long for the machinery we want to run on them. All our cables are on what we refer to as BS.4343 connectors (referred to elsewhere in this thread as CEE type 17 or Commando, although I've never heard a site sparky or HSE inspector refer to them as such) and the only way I've ever found to get my deWalt DW745 portable site saw or my 14cfm compressor to work consistently is to use the 32A sockets on the transformers (which have very large pins in comparison with the 16A ones, which in turn are larger than the 13A square pins on a domestic plug top) and the thickest single extension cable I can lay my hands on. Cheaper extension cables only have 1.5mm cross section wire in them. Heavy duty ones should have 2.5mm cross section and even thet can sometimes be too thin to start an 1800 watt (universal motor) saw at the end of a 15 metre (50ft) cable run. I first adopted a 4mm cross section cable when I bought the DW745 which fixed the issue, but I then needed to go to a 6mm cable a couple of years ago when I acquired the compressor (2.2kW induction motor) because the 4mm cable wouldn't always work. The circuits these go onto are generally just 20A MCB protected, so it isn't the MCB which is the limiting factor, it's the voltage drop caused by trying to use too thin a bit of "electric string". The downside of going to a 6mm cable, though, is that is set me back about £85 at the time, and it is also very "nickable" so it always has to be secured and locked up when not in use.
