Voltage drop to sub main.

[mattmoo1974]

I need to feed a new board 50m away.
Iv been doing clacs 16mm drops 7.2v over this distance. Is voltage drop to point of origin?
Does this mean im going to end up using 25mm?
Sorry if am being stupid,been there for hours and had info overload today :S
Hes got 2 water supplys in his house(not bonded)
There are 3 CCU's with 3036 fuses.
I did a Zs test on 1 of the rings at it was 30 ohms!.
Its got board feeding another board feeding another, Mix match of cable between each 1.
the 1 on the end is fed in 6mm and got 10mm coming out to feed the shower!
Hes buying the cable for the job even tho i can get it cheaper(hes buying from screwfix)
Iv also told his what hes putting in his new extention is way over the top for the supply.
I got the answer "well its the same as what iv got in here" hes got a AGA in his house and a 7500w hob going in down the other end. No shower in his part and a 10.5Kw going in the other. And he wants to put a waterheater 10Kw and 2x 3Kw panel heaters!
Diversity dont even go there. Do i just walk away? He thinks hes been coned cos they want 1100 quid to put the supply in.
Any suggestiuons would be helpfull only just started out and its turning into a mare.

 

[Guest 004]

oh what a picture you have painted for me, ROFL

 

[Dunc]

If you design at 5% VD, 16mm will be OK, from the origin of course

What about the rest of the installation? If the submain in 16mm just meets the 5% volt drop limit then wouldn't that leave you without any allowance for volt drop in all the other circuits from the secondary CU. Thought volt drop was always calculated to the furthest point so a light at the very end of the line wouldn't have a volt drop greater then 3% from the origin of the installation (the cut out/meter position).

 

[mattmoo1974]

thats how i worked it out dunc, 16mm was 7.2 after 50m so over.
Then 25mm was starting to cost the extra they want to move it. Plus im not brave enough to try and change CCU from Bs3036 to RCD and sort out the issues there, it needs a rewire. but "well its working now"

 

[ian.settle1]

Don't forget that when you are calculating for volt drop you have to take into consideration the the maximum volt drop is from the point of origin of the supply eg DNO incomer to the end of the final circuit on any DB. So that the total volt drop for al parts adds up to no more than 3 or 5 % from point of origin to end of final circuit.

 

[mattmoo1974]

Yeah i think 25mm left me with a 1 volt to play with then i had to deal with the 3 CCU's at the incomer and i thought fk dat.
So rang him and said get it put there. As per it all needs doing for doing for less then minimum wage