Best Practice / Design question ...

KingKenny · Sep 28, 2013

Hi everyone - I've not been around on here for a bit - hope everyone has had an enjoyable summer. - I have a quick question about best practice / design of a solution for a job I've been asked to consider.

In summary, I've been asked to reconnect an existing SWA supply to a byre (outbuilding) and to install fluoro lighting in this byre. If the supply is in good order, great, if not it's straightforward to replace. So far, so easy.

Now, there is a second outbuilding - a shed - with no existing supply. The shed will run a washing machine, tumble dryer and Fridge Freezer. I haven't yet assessed the load, by the way. The client (I haven't met him yet, the communication was by email) has asked if I can run a supply from the byre to the shed - this would be another new SWA cable, 600mm deep etc..

But - my question is this ... If done this way, wouldn't this supply simply be an extension of the existing (byre) supply, originating at the main CCU CB? If the byre only has 4 fluoro's this adds hardly any load, so I guess it could be done this way, but what about future expansion? - If the byre suddenly has a couple of ring mains added then load could become an issue back at the original board, no?

Would it be better to run the shed supply from it's own CB back at the Main CCU? There are spare ways, RCD protection appears sufficient.

Also, each of the appliances in the shed require their own SFCU - so is it better just to have each on their own radial or run a ring and spur FCU's off sockets?

Loads of ways of doing this, I guess, but I'd be interested in hearing your thoughts as to 'best practice'.

Thanks in advance, as always.

KK

Dizzy_Maskell · Sep 28, 2013

Many ways skin the cat but I think I would use a deprecate supply if each, easier for isolation purposes and own segregated circuit would be good,
Also if used for washing machine etc I have seen cases where older washing machines in sheds cause nuisance tripping so separate circuits at least keep power to original install.
But as always time and finances dictate the end job

Dizzy_Maskell · Sep 28, 2013

Separate supply to each building sorry predictive text out did me

ChrisElectrical88 · Sep 28, 2013

I would sit down with a pen and paper and draw out a couple of scenarios. There are plenty of ways of doing this.
Once you have a few plans in front of you pick out a couple which you think are the best and cost effective (even post them on here I am sure people will be more than happy to chip in if most of the donkey work is done by yourself) then you can price these up and maybe give the client a option 1 and option 2 and the benefits of each.

Octopus · Sep 28, 2013

Why are you planning on FCU's for the appliances, won't sockets suffice?

Rockingit · Sep 28, 2013

You need to sit down and do the load/cable maths for starters, and let that be your guide. If you can achieve an A>B>C scenario and be within the 3% allowable VD for lighting at B, then that would be the way I'd do it, just install a small sub board in the byre and take a radial feed off to the shed in SWA, then adapt into twin or singles/tube and do whatever you have to do.

If the size of the existing SWA is too small for your VD, then you'll have no choice but to run a second feed from origin.
[Assuming, of course, how bothered you think you need to be at complying with BGB VD requirements - it is possible to argue out of them!!]