ring circuit length concerns

[mrloy99]

When you think about it this installation should have been designed , 250 metres on a ring , way to big , ive had houses that have been large long cable runs and the calcs were to close to the mark for my liking so i installed the rings in 4mm just to get the readings to an exceptable level so realy the person doing the design of this one need to get back to the drawing board

I totally agree,But I think even with 4mm and Lennys recommended 26amps we end up with a maximum of 160metres to comply with the permitted voltage drop.I've voiced my concerns that we could be ending up with a voltage drop of 30volts.but I keep getting" there will be a very light load"I don't know if that means their design or rcbo will only be 15 amps(if that makes any difference or is permitted)
I know there is to be a wall mounted lcd tv in each of the 4 rooms on the ring...and also nothing stopping the residents plugging in their own personal kettle or suchlike...A sub dist board in a store would be the obvious way to go and also save them on cabling etc....but I'm only the numpty doing the work....All I can think of is to get their requirements in writing to protect my self from future comebacks

 

[nickblake]

Do you know what id do ,i would write down all your concerns on a piece of paper stick it in an envelope and send it to yourself dont open it ,just leave it , because if a problem arises from this ,and anything comes back to haunt you you are then covered by a your letter not saying anything will but you never know , but judging by what you have said i think a sub main would have been benificial in this case

 

[Steve Richards]

Are you signing the completion certificate as the designer, if no, where is your concern. the designer would take into consideration likely load and diversity.

I cannot understand Lennys theory where you multiply by 4, surely you multiply by 2 (2 x 2.5mm cables to the far end) and as I totally agree with your load of 26amps as an average gives you a circuit length of 49 metres.

A ring circuit 100 metres squared = 10 x 10 or 10 + 10 + 10 + 10 which is 40 metres of cable in total. Based upon the circuit being fully loaded at 32amps

2 x 11.5 x 1000/32 x 18 = 39.93 metres - am I missing something?

 

[Sintra]

Think about the formula for working out R1 + R2 on a ring

r1 + r2 / 4 = R1 + R2

Same principle applies.

 

[Steve Richards]

Of course.........Doh! thanks

 

[dixon9]

If the forman/designer insists on 2.5mm, Is it possible to use a 20A breaker instead of 32A and marking this as a deviation authorised by the designer in order to avoid volt drop issues?

Let´s face it, he´s the one saying "old people....very light load..."

If he doesn´t agree to the 20A breaker then he is pretty much admitting that he doesn´t really believe what he is telling you.

 

[nickblake]

Old people very light load lol who's he trying to kid , older people feel the cold ,example is my father in law central heating on plus a three bar 3kw electric fire so he is incorrect with that statement