Has anyone had the chance to work on relocating a CU and extending the meter tails? It looks like the new tails will need to be 6-8m long to satisfy the customers request. How did you go about this task if you've experienced this sort of job?
Extending meter tails.
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Terminate the existing tails into a fused switch as this will also give protection to the tails and extend from there. https://www.cef.co.uk/catalogue/categories/switch-fuses-sp-switch-fuses
This question has been categorically answered by Sidney in one fell swoop and needs no embellishment . In my 'umble opinion of course.
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Not sure that I 100% agree with that .................. surely the installation method of the "new tails" might lead to 1 or 2 additional questions and answers ....................
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One would have to choose an installation method that does not trigger a need for RCD protection of the tails.
How about a situation where the new CU location is longer than 3m away, and that intervening space will be boxed in, so that the new fused switch wont be accessable? If you move the new fused switch to next to the meter, or next to the CU you still end up with tails longer than 3m.
Is there a reg associated with keeping the tails less than 3m, or is it just accepted practice? Sorry, what I'm saying I guess is, what are we trying to fulfil by doing so?
**edit** that's weird, @ProDave's reply wasn't there when I typed this in. Thanks Dave
**2nd edit** just scoobed you for that Dave, and brought the scoob total to zero. Which means someone de-scoobed you. That's just mean
Is there a reg associated with keeping the tails less than 3m, or is it just accepted practice? Sorry, what I'm saying I guess is, what are we trying to fulfil by doing so?
**edit** that's weird, @ProDave's reply wasn't there when I typed this in. Thanks Dave
**2nd edit** just scoobed you for that Dave, and brought the scoob total to zero. Which means someone de-scoobed you. That's just mean
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I believe the general DNO approach is that <=3m is acceptable, though quite often long tails are installed in new builds and different DNOs may have different standards I am sure one of them has 4m as the maximum length.
Section 433 mentions 3m as a maximum distance so long as the cables beforehand are installed so they are not likely to overload.
If there is a short single length of protected cable that is safe from overload the protective device can be installed after that section without significant danger, presumably it is thought that lengths over 3m cannot be sufficiently safe to allow this. Practically, in most cases if there is not a space within 3m to fit a switch fuse then it is a very restricted area.
I quite agree but the OP has left us guessing ......................... so best not we take assumptions ..................
It seemed simple to me ............ the C/U is moved 6 to 8 mtrs away ...so fit a sw/fuse and install tails to the C/U . We don't know what method to apply so Occam's Razor applies .
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Somewhere in the dim and distant recesses of my brain I recall something called "CM16 conditional rating of double covered meter tails"
this applied to,the 3m tail length not needing OC protection.....but I am burgered if I can find it anywhere
this applied to,the 3m tail length not needing OC protection.....but I am burgered if I can find it anywhere
I remember it as .....most DNOs stipulated meter tails up to 3 mtrs long could be protected by their cut-out fuse . Longer than 3M a sw/fuse should be fitted to discriminate over theirs .
Then with the 17th we were blessed with fitting an overall ( & unwanted) RCD depending on the install method of the tails.
Eventually there will be so many regs prevailing that you won't be able to do anything . Houses will be wired in surface mounted 25mm steel conduit radiating from a 4 X 4 steel trunking from end to the other .
Ring mains will be banned ..all sockets will be 60A Commando radials wired in 16mm SWA also surface ...in case someone wants to to do some arc welding in the house .
Consumer units will made from 1/4 " steel plate with welded seams
Then with the 17th we were blessed with fitting an overall ( & unwanted) RCD depending on the install method of the tails.
Eventually there will be so many regs prevailing that you won't be able to do anything . Houses will be wired in surface mounted 25mm steel conduit radiating from a 4 X 4 steel trunking from end to the other .
Ring mains will be banned ..all sockets will be 60A Commando radials wired in 16mm SWA also surface ...in case someone wants to to do some arc welding in the house .
Consumer units will made from 1/4 " steel plate with welded seams
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The reason for the "3 metre rule" is nothing to do with the DNO, it is part of the wiring regs, concerning positioning of an OCPD [which as we all know is intended to protect the circuit cable]
Apart from in certain rare instances, the thing has to be positioned either at the point where the current carrying capacity of the cable reduces, or, within a maximum of 3 metres of that point.. [Ignore the fact that i would think that half the time. 25mm tails have a larger current carrying capacity than the house service cable]
Anyway, the DNO will not allow you to assume that THEIR fuse will protect YOUR cable, and so, if the CU is further than 3 metres from the METER [i would say, see later] then you will need to provide an OCPD somewhere within the three metres from the METER to the CU.
Ok, the "from the meter" bit...
The tails from the cutout to the meter, are, as the DNO will eagerly point out if you mess with them, nothing to do with you, they belong [or so they like to think] to the DNO.
BS7671 does not apply to the DNO, it only applies to YOU, and where do YOUR bit of the tails start?? At the meter.. So, do not worry what is before the meter, not your problem and nothing to do with you, and nothing to do with BS7671 either..
john..
Apart from in certain rare instances, the thing has to be positioned either at the point where the current carrying capacity of the cable reduces, or, within a maximum of 3 metres of that point.. [Ignore the fact that i would think that half the time. 25mm tails have a larger current carrying capacity than the house service cable]
Anyway, the DNO will not allow you to assume that THEIR fuse will protect YOUR cable, and so, if the CU is further than 3 metres from the METER [i would say, see later] then you will need to provide an OCPD somewhere within the three metres from the METER to the CU.
Ok, the "from the meter" bit...
The tails from the cutout to the meter, are, as the DNO will eagerly point out if you mess with them, nothing to do with you, they belong [or so they like to think] to the DNO.
BS7671 does not apply to the DNO, it only applies to YOU, and where do YOUR bit of the tails start?? At the meter.. So, do not worry what is before the meter, not your problem and nothing to do with you, and nothing to do with BS7671 either..
john..
Sharpend
"It Just Is"
That’s not strictly true John.
Risteard
Senior Member
Firstly it's not necessarily 3m - the length varies between different DNOs (e.g. some might be 2m or 4m) although 3m is a common length quoted. Secondly selectivity (discrimination) doesn't come into it - your BS88 fuse won't discriminate with theirs. It's simply that they won't accept liability for their fuse providing protection to your installation beyond that length. That doesn't mean it won't be their fuse or both fuses which operate if there is a fault.
