Yes ok Spin but knowing Col as we do on here i'm sure he knows that it needs to be a fuse as well as an isolator.
To be fair the highlighted paragraph i posted from UK power networks does say a "switch fuse or isolating switch"
Who knows? I thought he was asking how long the tails could be without installing a protective device at the start of the run. Was trying to explain that BS7671 allows 3m. Yes individual DNOs will have their own requirements, which may or may not tally with BS7671.
BS7671 stipulates the max length of an unprotected conductor. DNO's can stipulate whatever they want, they don't work to BS7671.
So to surmise: all these houses which have been carved up in to flats and have 10, 20 metre tails on the DNO's service fuse are wrong!
I've always been happy with an isolator so long as the run is less than the max Zs permiteted by the cut out fuse. What would be the point of putting in a 60a sw on a 60a cut out fuse? How would that possibly be any safer than just the one fuse?
Spin those regs have nothing to do with tail length, those people at the metering site have misunderstood them too.
I take it that you guys are aware that BS7671 only covers the installation and not the distributor's equipment? Are you also aware that except in exceptionally rare circumstances where many conditions would first have to be agreed, the DNO's do not allow their fuse to provide protection for an installation? If you can't grasp any of the above, just explain why the DNO's limit the length of the installation's tails.
I always stick in a KMF regardless if its a new install, what we looking £28.00 all in, but saying that, the last meter monkey who came to connect two pieces of 25mm tails sheared the threads in mine so I never trust that lot. I see there still banging on about seals being cut and fuses pulled, bring it on as what they intend to prosecute you for, working safe or complicating your daily routine and worrying about their profit margin on having a guy in a van driving round with a pair of sealing pliers. . .Pfft!
Mate the DNO don't have any requirments to keep the tails to three meters, if there WAS a requirment then it would be made statutory - there is NO law covering this. Every time I've called to ask about this all they say is anything beyond the meter is nowt to do with us. They might WANT the length of tail between the cut out and the meter to be less than 3m but that's up to them. If you have a cut out rated at 60a and you put in a sw fuse rated at 60a after the meter than you will have two 60a fuses in series. There has NEVER EVER been a requirment for this under BS7671. EVER! In fact you could end up breaching regs for not providing discrimation. In the event of a fault, most likely both fuses would blow meaning both would need to be replaced! Proving the Zs and volt drop is within limits there is technically no reason NOT to use the cut out to provide protection. The electricity doesn't magically change 3m down the cable, it's the same as any other standard final ctt, except it has a meter on it. Would you do the whole hog and provide two CU's or fit two 13a fuses for every fused spur you wire? Hopefully one day a few of you might well have a bit of an epifany and realise that what I propose is NO LESS SAFE than two switch fuse in series and does not breach any regs
Well Coloumb they do have requirements to keep the maximum length to on average 3 meters maximum I've listed 3 of them.. beyond 3 meters you should fit a switch fuse or as UKPN said an isolator, I'm not saying its to do with the fusing down or using there fuse for protection, there would appear to be a slight grey are when it comes to that, although having two 100 / 80 in series at the meter cant be a bad thing necessarily, its not like if both go you loose more then that circuit anyway.. Still the suppliers don't seem to give a specific reason for it but one I would surmise, especially as UKPN mention an Isolator is the ability to de-energise the supply into the building at close to the source as possible. It would appear to me to be pretty dangerous to have a live supply running through a building for any considerable distance (more the 3 meters) without the ability to turn it off if needed.
Caddy mate I should have said, you DEFFO need an isolator at the start of the run. Sozza. But not a switch fuse. Agree that 100/80 in series is fine. Still maintain no one has come up with any proof that any DNO require less than 3m. If they did then they would need to disconect quite a few supplies.
Well perhaps not require but advise / recommend.. There are a lot of installations that need disconnecting that have nothing to do with meter tail length I'm not sure why you don't think the highlighted statement from UKPN is proff that they require a maximum length all be it 4 meters not 3
But look mate it says switch fuse OR isolating switch. If it said SW only I would agree but even the DNO are happy with just an isolator
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