Discuss Volts drop too high... in the Business Related area at ElectriciansForums.net

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Morning Chaps,

Thanks for your continued assistance. It is looking rather like the calcs will fail.

Does it matter that the building is empty and unlikely to be used for anything other than visiter centre in the summer?

What is the maximum LOR for RFC? 120 Meters is roughly worked out, lets say it would be the worst case. It is more likely to be about 100m if measured with a tape measure

If we calc 18 x 20 x 100 / 4000 = 9

Would it be acceptable to show these calcs?

ALso, should a job like this come up in the future how would I get round the VD?

Surely you wouldn't wire a RFC in 4mm? And there is nothing I could do about the LOR. It is purely down to distance from the DB

And my final question would be.... Am I correct in stating LOR as beggining at DB going to every socket and include the return leg to DB?
 
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Morning B

As Tel and I were saying in the real world your 120m RFC will most likely never cause you a problem and would chug away happily but you said you needed to show calcs, and on paper it is non compliant with VD

If you use the OSG guide of 106m for a normal 2.5 RFC it would calculate @ 26.5 x 18 x 26/ 1000 = 12.402 v then you have your correction factor of 0.923 that would bring it to 11.45volts & your 5% is 11.5volts

So rule of thumb is the 100 sq mt one as maximum

I have seen RFC wired in 4mm, in fact for IT solutions if I decide to use a ring final I would do it is 4mm. This though is not for VD but to adhere to the regs with regards to protective conductor currents. So a 4mm ring would be fine, in fact a 4mm ring would give you an approx sq area of 175mt
 
It's a longshot but can you re-route some of the cables and make it 14m shorter? You wouldn't have to show calcs just quote the OSG if you could.
 
Just a bit of food did thought. I don't do much domestic more industrial but I am currently working with sparks who do quite a bit. The subject of ring mains and NIC inspections come up. At his last inspection the NIC inspector told him that a ring should be no more than 100M. Based on this a ring of 120 M is incorrect anyway.
 
I have heard 100 square meters from them not 100 mtrs, not sure what the difference is or even if it is true, I always have at least 3 rings in a house anyway and it is never anywhere that amount of length so I don't take any notice about that rule, even if there is something in it, and ahem there may not be, quick check the regs.
 
As Malcomsandford said,OSG table 7.1 gives you max length of 106m for 2.5mm , table H2.1 gives the 100m2 floor area.

Using 4mm it's 176m , not as uncommon as you think. Plenty of designers now are covering themselves by upping the cable size if the calcs are close.
 
yeah thats very true durham, a few consultancy's I do work for specify 4mm2 as standard now and also it has to be LSF too.
 

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