ring design and voltage drop

[i=p/u]

nice sums malcom, but can you say lets say you have values for r1 r2 rn... if you designing or longest possible

That is how I work out the length and volt drop in a Ring.

Length

2.5mm T&E ring.
1 conductor 2.5mm CSA @ 7.41mohm/m
1 conductor 1.5mm CSA @ 12.10mohm/m
{from page 166 OSG}

so if you have a measured value of say

r1 @ 0.58/7.41 x 1000 = 78.27m
rn @ 0.58/7.41 x 1000 = 78.27m
r2 @ 0.96/12.10 x 1000 = 79.33m

Volt Drop

Divide the length by 4 = 19.57 x 18 x 26/ 1000 = 9.16v

Bs 7671 pg 258, 6.1 correction for operating temp.

This calculation give you a ct of .923, x 9.16 = 8.45v

or

4 x 8.45v x 1000/26/18 = 72.22 / .923 = 78.24m

It assumes 20 amp at the furthest point and 12 amp distributed evenly around the ring so,

average = (32 + 20)/2 = 26 which is the value that Lenny posted.

 

[i=p/u]

so is the moral of the story, dont go over 100m meteres of 2.5mm on a A1 ring circuit???

 

[Deleted member 26818]

I believe it's 10m for 2.5mm² protected by a 32A B type MCB.
That's according to Table 7.1 in the OSG.

 

[i=p/u]

kooool spin london was there all along, knowing the sums is good tho

 

[Deleted member 26818]

Sorry that should be 106m not 10m.
Don't seem to be able to edit it for some reason?

 

[i=p/u]

knew what you ment .... and that 106m meter from table 7.1, does this include the approriate disconnection time???

 

[i=p/u]

yes sorry