cable length ring cct

d o'c

Is there a maximum run length for 2.5 T&E when used in ring ccts

The consumer unit is planned for the utility, which is back to back with the kitchen, so close to heaviest loads. Both these rooms are toward one end of the length of the building

However some bedrooms sockets are 22m from the CU, opposite end.

Splitting up into multiple rings I can easily keep the cable area coverage down, but it’s the long run until I get to the first socket on the far away rooms that I’m concerned about.

M cebee

was on a similar first fix yesterday -fuseboard in utility
used 4 radials for kitchen/ utility
and 2 rings for the long runs



100m2 is the floor area allowed -after that the 4%VD and Zl for the MCB are prob the limiting factors

you could always de-rate them to 20amp - anyhow

i reckon you'll prob be ok-go with the rings anyhow imo

2011

you could always de-rate them to 20amp - anyhow

The last edition of the regs will not allow this, I have not checked it in this edition but I think it is the same.

M cebee

enquired recently about this(my inspector) -was told it's acceptable



then again the rules may show 32-


i don't normally de-rate anyhow

but i've been on large jobs all wired in 4sq rings /20amp rcbos go figure

ft9

I thought ring circuits were not allowed anymore?

M cebee

ft9 wrote: »

I thought ring circuits were not allowed anymore?

not in kitchens

d o'c

I can keep well within the 100m2 for the rings. Another thought I had was to move the CU to the inner kitchen wall, I'd gain 12-13 metres (L shape) closer to the 'centre' of the building, but I'd rather not as the layout of the first floor make feeding cable much more difficult.

how can I get a ballpark figure for say 100m of 2.5 T&E IZ max, disregarding for a minute, ambient cond, temp, routing etc.

I will be able to route the longer runs down my service ailse behind the purlin,not bunched up near insulation, and I've fitted 25mm conduits,so things shundn't get too cosy

M cebee

if you mean the Zl at the socket on a ring circuit using 100m of 2.5 T+E

http://myweb.tiscali.co.uk/gospry/gospry2_033.htm

a 100m run gives an R1+R2(uk terminology) of 0.48

add that to your external fault loop impedance if you have it- and that's your Zl

the max ZL of 0.9 for B32 allows for 0.4 ohms on the supply fault loop using those figures