Circuit design for new extension

[telectrix]

could the rpm be a typo, should be 2800?

 

[Marvo]

Yeah, something doesn't add up with the figures given. It would be an absolutely enormous lathe requiring that supply stated in the op.

 

[ackbarthestar]

You are talking complete and utter garbage.

A note to every one, look at the RPM!

Who?, Garbage ?, Moi ? - lol

 

[davidcaulfield]

Ok how would you calculate a 25meter run through a loft. The demand is 2 pendants and 2 heaters and a kettle. Tncs system

 

[ackbarthestar]

Ok how would you calculate a 25meter run through a loft. The demand is 2 pendants and 2 heaters and a kettle. Tncs system

There were a whole load of very good sticky posts explaining the basics of cable selection. I can't seem to find them, but then I haven't really looked.

Three things to consider
1/ the method of earthing and any corresponding fault currents
2/ sub main circuit design
3/ Final circuit design

 

[Damian Petsas]

Hi guys, Ive just come from a house to loo at a outbuilding they have. Its curently fed from the house C/U. The C/U main switch is a 80 amp rcd switch. The Outbuilding is fed by a 6mm armoured with arun of about 15 m off a 15amp mcb. it goes into to outbuilding to a 13 amp spur. From the SINGLE spur it feeds 3 radials 1 to 2 double gang sockets, the second to another 2 double gang sockets the the third to a lighting circuit of 4 lamps.

Seriously not right!!!!!......

If i was to remove the first radial and allow the second radial of sockets and spur off that for the lights supply would that confirm to bs7671.

Would it be more practical to install a garage board and break circuits down from that and uprate the supply mcb to 30amp (its a old board)

your advice and knowledge would be most helpful..

 

[davethsparky]

Put a fused spur to cover the lighting circuit and the rest is likely to be messy but not strictly unacceptable. But without seeing it who could possibly say?

 

[Damian Petsas]

I know it couldnt get any messier I had to disconnect the first radial as it was on the supply side of the 13 amp fused spur.

just trying to accomodate the client and keep it decent. so if i had one radial and then spured the lighting off that its within regs??

 

[davethsparky]

What was up with the radial on the supply side of the spur? You said its on a 15amp circuit at the CU.

 

[Damian Petsas]

other than the sockets smashed to **** not a lot . is a garage unit a over kill you think??

 

[davethsparky]

Sorry my crystal ball isn't showing a very clear image at the moment so I couldn't see that they are broken. You made it sound like the only concern was purely technical not physical damage.

Only you can decide what is best for the situation after looking at it. In a purely theoretical sense what you have there is not overly bad but the physical condition of it is quite possibly appalling.
I think we have all been to these places where DIY dad has added a bit her and a bit there over the years and can picture the knitted mess of cables you may be facing, but without seeing it what do you expect people to say?

 

[Damian Petsas]

I appreciate your help and yea it certainly is a diy disaster dad job. You have helped buddy appreciate it. ps if i find a crystal ball there ill be sure to send it over lol, Have a good weekend mate.

 

[shagbite]

if the house's earthing supply is pme, you should consider running a 10mm green and yellow 6491x from the MET, to bond the pipes on the bog.

also, are you sure that there's rcd protection on this board. the main switch on a domestic cu doesn't usually have earth fault protection.

 

[davethsparky]

Bog? Lol I see where you got that from but I think he meant to say look at an outbuilding, I read it as a loo in an outbuilding at first too.

 

[shagbite]

hahaha! well spotted.

 

[Damian Petsas]

lmao that was supposed to be look. clearly im not supposed to be sat at a computer lol. The main incommer on this install is a 30ma rcd rated at 80 amp. it is a pme system and as its an old 3871 mcb type board can only think that the easiest way they could fit a rcd to the install.

 

[Richard Burns]

Electrically apart from the lighting not being fused down to 3A the system is fine, there is the potential for ready tripping of the supply if overloaded but that is just nuisance and not dangerous.

Put both socket radials on the supply side of the FCU and put a 3A fuse in for the lighting and you are done.

 

[Damian Petsas]

superb advice and many thanks Richard. quick qestion as there is a 30 ma rcd as an incommer does the 0.4 s disconnection times for all under 32 amp and 5 s for over still apply or is it all 0.4 s

 

[davethsparky]

By the sounds of it this installation is in a very poor state of repair so may need a little more than just changing the the connections have been made.

 

[Richard Burns]

So long as you have a TN system then the disconnection times do not change because there is an RCD in place.
So distribution circuits and finals over 32A are 5s and finals under 32A are 0.4s