Been to a customers today to price laying a patio.(great weather )The customer has already laid the base(solid concrete, 12 inches thick!) and underneath has run the swa to feed his shed.(2.5mm only)
The swa is to be jointed into the utiliy room ring via a fcu,on this dedicated ring is washing machine and tumble dryer.Measurements as follows:-
cu to fcu point=15m
fcu to edge of patio = 4m
patio to shed =20m
All the elderly chap wants is to run 1 light and 1 double socket for his woodworking hobby,nothing to serious at all.
Question is,would this set up be alright for the full length in 2.5mm?
If not, could he do an external/underground joint from the edge of the patio and joint the 2.5 to two 2.5's (he has got enough left over,so therefore making the 20m run from the patio to the shed 5mm)
If none of the above look like a good idea then i'll have to do what i don't want to do,dig up his concrete base
Please bear in mind i'm only a humble brickie so if none of my ideas sound sensible,dont shout to loud!

    Thanks in advance.

thanks jonny,as long as i dont have to dig up and as long as his drill turns i'm happy
All the works are to be done by his sparkie (or himself,not me),i just didnt want a phone call after i'd finished asking me to dig up and re-lay the patio!I'll tell him the info and put the ball in his court,thanks again.

They would have to be exactly equal lengths of cable, as if one was slightly longer, the majority of current would travel through the shorter, lower-resistance cable, potentially overloading it.  You've also got the issue of two seperate supplies terminating at one point.  The only option would be to treat each cable as a seperate supply, with an FCU for each, but you'd have to label the fact you have two incoming supplies in the shed.  This is feasible, but 13A should be sufficient for his needs anyway.
Glad you noticed the comment, i won't mention plumbers...!! lol!

[quote author=supersparky  link=1098546631/0#6 date=1098559778]if you wanted to be future proof you could stick some duct in along the surface- ie just cut a channel [/quote]

You are the expert so I'm not questioning the advice - but I thought the regs required cables to be buried at some depth and covered with warning tape etc?

Andrew

were talking at cross purposes here
look at my reply
then see the reg you quoted lol

its SWA so will have earthed protection

it will be buried to a depth to prevent damage in the future...its a patio and although this could be disputed, its not likly to be dug up every 5 mins

and the 'warning tape or other cover'
hence i said ducting



ss

The regs to recognise doubled up cables, but it is beond the scope of most people to fit such a system - and I wouldn't want to see it anyway.

Doubling up cables...I can't believe I am reading this....Noone here can be any sort of qualified electrician, otherwise the penny would drop that they are talking about a perfectly standard ring main here...just configured in a slightly different way...no wonder you can't rely on the so called experts to do anything right...

[quote author=qw  link=1098546631/0#13 date=1099061963]Doubling up cables...I can't believe I am reading this....Noone here can be any sort of qualified electrician, otherwise the penny would drop that they are talking about a perfectly standard ring main here...just configured in a slightly different way...no wonder you can't rely on the so called experts to do anything right... [/quote]

And where did you train?..

I strongly question your judgment!  

I must say that i asked a sensible(to me anyway ???) question and by consensus of opinion (ie the majority,if not all replies ) said or replied in the same way to it,so as far as i am concerned these respondees (where did i get that word from ) are correct.
 Now to all those, whom i gratefully respect, for answering,(as i've said before,i am just a bricky with VERY basic  knowledge of electricity ) can you explain what is the difference in what i thought could be done (connecting 1 feed to 2 cables to the shed) as opposed to a ring as qw says is all that i thought of!
As i have said,this isn't an 'argumentative' question,it's just not being a sparky,i can see where he's coming from! (even if the current crop of replies is  telling me he's talking tripe)
SO what exactly is the difference?

Can I ask a quick question here?  If the cable is rated at 20 amps, how is it that you can use a 32a MCB?

My understanding is:

Design current </= Protective device </= Cable rating

I presume there is some 'correction' to be applied because it is a ring?

I need to know, my exams are soon  

but 2/3 of 32 amps is 21.33 amps, still more than the 20 amp rating of the cable.  How is this allowed?

[quote author=JerryD  link=1098546631/15#20 date=1099090875]but 2/3 of 32 amps is 21.33 amps, still more than the 20 amp rating of the cable.  How is this allowed? [/quote]

I want to put this to rest  

but to awnser your question, ring mains are an exception where the IEE regulations set out the maxium floor area surved, the type and size of cable that can be used, and maxium cable length

This allows a ring main of 32A using 2.5mm Twin+Earth Cable + 100M of Cable in total.

You could as an alternative have a Radial of 50m of 2.5mm T+E on a 20A CC

Or Radial of 100m with 4mm Twin Cable, with a CB rated at 32A..

[quote author=JerryD  link=1098546631/15#20 date=1099090875]but 2/3 of 32 amps is 21.33 amps, still more than the 20 amp rating of the cable.  How is this allowed? [/quote]
burried in a normal non insulating wall counts as method 1 (the same as clipped direct) and the rating of 2.5mm in that situation is considerablly more than 20A (though not as high as 32A)

[quote author=sparkyjonny  link=1098546631/15#25 date=1099236723]22 or 24A from the top of my head? [/quote]

Table 4D5A says clipped direct has CCC of 27A

Read that awhile back, the findings was the important bit  8)

or in my case 1.5mm

the answer is those who see the current ratings in the sheds and don't know about the concept of voltage drop (or don't realise its significant)

also i still think you can get away with a lot more voltage drop than the regs allow for

And there was I thinking that volt-drop was affected by the electrical resistance of the cable too........!

TT

[quote author=plugwash  link=1098546631/30#30 date=1100541204]
also i still think you can get away with a lot more voltage drop than the regs allow for

[/quote]

That's not the point

Quote:


And they seem to forget about expansion..

Quote:


Well quite a few people it seems, its got to be better than 1.5mm unprotected flex tho