Maximum lenght of tails from isolation switch

[str]

Am planning to have my electricity meter relocated and an isolation switch installed by my provider and then have the consumer unit relocated

is there a maximum distance/length of tails between the isolation switch and consumer unit? I could be looking at around a 7 or 8m run by the time the cable goes down the wall, under the floor and then back up to connect to the consumer unit.

 

[rebuke]

I'm not sure what the limit is off the top of my head, but you can deal with it by putting a switchfuse in if necessary instead of just an isolator.

 

[Jaymack]

Why not ask the provider, if they're installing the "isolator" which is probably a DP MCB, they will want to be assured that this will protect the cable.

Regards

 

[electronicsuk]

I've heard of various DNO imposed limits, but never anything longer than 5 metres, so you can be fairly sure that they wont allow 8m. In any case, if the cable is going to be run enclosed in a wall then you don't want to be using tails, otherwise you would be forced to RCD protect @ 30mA. In doing so, it would also make it difficult to comply with other regulations regarding minimizing the affects on multiple circuits if a fault develops.

You could circumvent the need for an RCD by burying >50mm in the wall, but if I were doing the work I wouldn't be happy to do that. The run really needs to have earthed metallic protection, and the easiest way to comply will be via use of SWA or Split Con. Neither of these could really be terminated directly into the meter anyway, so you might as well have a switchfuse installed. This kills two birds with one stone as the supplier then has no reason for concern over the length of tails, and it also provides a convenient means of terminating the cable.

 

[Taylortwocities]

AFAIK split con does not comply with the requirement for earthed mechanical protection for concealed conductors.
SWA is the option/

He'll need a switchfuse - probably 80A - depending on the DNO's service fuse size.

 

[too old to learn]

problem with SWA is that you can not terminate it correctly in the usual new consumer units that people buy from various sheds. the last thing they want is a new consumer unit with a metal clad box sitting right near it.

personally I wouldnt use SWA for running cables inside the house, mainly use it for external wiring.

As long as you run and tie the tails to the middle of the joists (therefore normally more then the 50mm safe distance) then this should be all right (IMO of course).

Again, there is a large discussion on how long your tails can be, and these can vary from to who ever you speak to at the DNO, depending on how happy they are in themselves on a specific day.

I always say, 5m or less then connect them straight up to an isolation switch at the meter (i would never pull the fuse ) more then 5m then im afraid you have the added cost of a switch fuse, approx £80 for 80A. Then of course you have the dilemma of what size fuse is in the cutout

 

[Albert]

The last time I had "long tails" to deal with the limit was 3m, but I think it depends on the DNO. There was no requirement for switchfuse, they asked for DP isolator only.