Granny Flat

[eco-tech]

I was asked to do some work on a shop etc.

What the lad wants is a new board and a sub mtr in extenstion he built.

He has a 3 phase supply to his shop and he wants me to take a feed from this to the new board ect.

What he has done is pull x2 twin and earths 6mm cables from his 3 phase supply.
Will this be enough to feed the new board ?
He is having 6 sockets
4 lights
electric oil heating x4
Small kitchen
cooker point

I think 10mm from the old 3 phase board ?

Any help chaps ?

 

[malcolmsanford]

Well you need to factor in quite a lot more information

How it is going to be run, are there any rating factors, how long the run is, what is the loading for the board. As you are going to design this you will need to know how your going to install them heaters on single radials, or whatever. Then your going to have to design the kitchen power, the cooker power, and lights. So you will need to know your loads. You never mentioned sockets I assume there is going to be some?

If I understand you correctly it is going to be a 230v single phase supply to sub board. So the 2 x 6mm T+E I assume are going to be doubled to make 12mm conductors? Not what I would have done. If your going to use T+E I would have used minimum 16mm for a sub board after ALL CALCULATIONS telling me that 16mm is ample. There is nothing in the regs stopping you using conductors in parellel, in fact there is a section just for that, but that is normally used with much bigger cable than your going to use. If I'm right about the doubling of conductors just seems to be a cheap option.

I assume the sub meter is going to be a private meter not DNO. The DNO would most likely not connect to a T+E supply they would insisit on SWA or concentric

 

[eco-tech]

Yes I'm looking at using swa for the feed in.
Kitchen only has 2 sockets
Heaters will be on a radials
The run length for the feed in is 15 mtrs tops
Yes its a landlords sub mtr.
He dont want to pay big money for cable etc and i think this is y he run the 2 (6mm) in to double up.
It would be ok in this doubled up but i think using swa is better ?
Dont have any problems with the lighting or ring or radials but just need to make sure it's correct.
only putting in a 6 way board (rcd)

 

[malcolmsanford]

Your Earth from those 2x6mm cable will be 5mm not good enough. You could do the equation but I would not be happy with a sub main earth of less than 6mm and even then your going to have to prove that 6mm is capable of carrying the fault currents from your load. 15mts of 16mm say SWA is not that much.

Also how are you supplying the submain. You say your taking a single phase from a 3 phase supply, is that direct from the head or from a 3 pahse board. If it's from the head via the 3 phase meter, what service fuse is in it?

Is it just the a bedsit? Surely the frontroom and bedroom will want sockets.

 

[eco-tech]

Its a bed sit very basic.
The feed will come direct from the shops 3 phase board and into the new single phase board.
Do you Think a 10mm earth from the 3 phase board would do the trick ?

 

[eco-tech]

Would a 10mm 3 core swa do the job ?

 

[telectrix]

i'd use 16mm SWA after checking load, volt drop etc.

 

[eco-tech]

thats big ffs

It going to cost him now ohhhhhhhhhhh ha ha ha ha haha ah ha ah aha h