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]

sounds like a complete rewire, dont walk away think of a price and treble it!

 

[IQ Electrical]

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.

At the end of the day, it is what it is whether that's 16mm or 95mm and as the designer and installer, you either install it to those parameters or walk away.

I hope it's a TT system with the socket Zs value?

 

[mattmoo1974]

I dont think his new supply is man enough for what he wants to do tbh.

 

[mattmoo1974]

TNCS! think i ll walk away.

 

[Guest 004]

you can always put that circuit on an RCBO

 

[Guest 004]

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

 

[IQ Electrical]

you can always put that circuit on an RCBO

You can but there's still a latent defect somewhere on a system that you are relying on to provide ADS on the prospective new install, 30 Ohms isn't from a long run....

 

[Guest 004]

yeah probably just an earth thats come away from the back of a socket, and just resting on the terminal. Or the corner shop socket has been wired as well

 

[mattmoo1974]

Its 1 big radial with 3 CCu's along the way and a 8.5Kw whacked on the end and the ring and some ermz Nice down lighters.
Iv told him to ring the DNO and get the supply fitted to extention and explained AGAIN that the set up in there is far from good and needs looking at ASAP

 

[Guest 004]

What was the Zs of the 10Kw heater?

 

[mattmoo1974]

I didnt do that but i ll have a look tomoz she was washing some 1s hair while i was there!

 

[empress]

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.

walk away if yer got any sense.
trust me

 

[Guest 004]

Most probably will not comply. No actually it WILL not comply, with the length of run already stated, and going down to a 6mm, then back up to a 10mm, and when you tell him it needs a total rewire, I bet he says, 'well it's working ok now'
LMAO, sorry but good luck,

 

[mattmoo1974]

you wont believe how may times iv heard "Well its working ok now" in the last 2 days!
Iv told him to have 1 of the supplys fitted at the extention. As it would be cheaper option :d and i dont have to play with the largest Radial Circuit in devon
And advised him to look into gas cooker and water heater.

 

[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