length of ring main circuit

[davidjones89]

Its a ring main so 2x2.5mm conductors, you will be in on Vd by a country mile!

now thats what i was thinking, and you are the first to say so

 

[High Tower]

i fancy paying it off the roll and then when its short i will get wholesaler to coil it back up and grovel to me for selling me less than i asked for!! if it is 100m then i donald ducked and will have a snotty pile of cable!!

Ha ha that i would love to see!! you with a massive pile of payed out cable all over your drive!!

 

[DaveyD]

my problem is if you use any length near to the maximum you do not comply with the volt drop ! am i missing something ?

Page 51 Table 7.1 Notes ..."Voltage drop is the limiting constraint on length" ....

But you have the wisdom of other posters too

 

[davidjones89]

To find max cable length on ring allowing for volt drop use formula

4 x max vd x 1000 / ib x mV/A/M

just give a bit more light on this formula please,
4 x 11.5 x 1000 divide by design current x mV /A /M ?

 

[High Tower]

u got it

 

[davidjones89]

u got it

not so sure, 4 x 11.5 x 1000 divide by 32 x 18

 

[IQ Electrical]

Don't confuse length of ring with max floor area, I think the max length limited by volt drop is around 127M allowing design current of 20A

 

[High Tower]

I said you explination of the formula was correct but where do you get your numbers from??

4 x 11.5 x1000 is correct but your Ib will not always be the max admissible current allowed but in a ring that is correct. however i cannot check your mV/a/m as i dont have the regs to hand.

 

[davidjones89]

I said you explination of the formula was correct but where do you get your numbers from??

4 x 11.5 x1000 is correct but your Ib will not always be the max admissible current allowed but in a ring that is correct. however i cannot check your mV/a/m as i dont have the regs to hand.

volt drop for 2.5 is 18, using the mcb of 32a as Ib. kitchen ring main has got me thinking in a barn conversion, due to the above size rooms to a standard house. It is measuring out at about 53 metres, just applying the maths to it and getting my head around it