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Topic Title: Meter Tails Restrictions On Length - Reg No. anyone please?
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Created On: 04 November 2009 09:46 PM
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 04 November 2009 09:46 PM
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paulskyrme

Posts: 758
Joined: 12 February 2003

I was asked today to look at a job where the customer has sheathed singles running around 8m through the fabric of the building to a board.
Now as we all know these are NOT meter tails! More a sub main.

I say, as it stands the material & route are unsitable.

There is no main switch for the whole installation.

It is domestic with 4 boards adjacent to the meter, this sub main to another board elsewhere in the building, one is also subbed off another.
Also a sub main to an outhouse fed via a Wylex fuse/switch 60A via 25mm sq 3 core swa about 35m approx.
This has a sub main to 2 more boards, one of which has a sub main to another! These both have 30mA up front RCD's, discrimination...Not!

All of these are fed from a 5 way DP service connector block.

Obviously alarm bells are ringing here.

The tails are all 25mmsq, so "OK" on a 100A 1361

Can't find the DNO requirements on WPD site the link I think I need seems to be "down".

I was asked to look as they want to re-locate their meter and cut out and was asked what was involved!!!

I have spent an hour or so going through the big red bumper fun book & I can't find a reg limiting the length of cable protected by the DNO cut out. Anyone please? Tried 433 none seem to be exact?

Oh and to cap it all no real circuit ID's on the board, no certs at all for any previous work, no labelling, both colours in use as well.

Methinks first before any work full PIR!

Thanks
Paul
 04 November 2009 09:56 PM
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slittle

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Paul,

I'm fairly certain it's a DNO requirement rather than the red book.

I know it varies area to area as well. Alan Capon is probably your best man on here but he's a Manx man so again their rules may differ to WPD.

I'm in EDF land and if it helps, it's normally 3m but they will sometimes let you have 4m if it's an external box.

Regards

Stu
 04 November 2009 10:37 PM
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Legh

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The Big Red book at bedtime says try this one: 434.2.1

Legh

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Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 05 November 2009 12:15 AM
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pmenetwork

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this is a meter operator requirement, as it he/she connecting. 3 is normally the max, but as stu says, can stretch to 4 metres. best in trunking, though, for that kind of length. sounds like that meter pos needs tidying up!
 10 June 2010 10:53 PM
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chevalier

Posts: 61
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Have a look at Electrician FAQ which gives advice in these situations. The length of meter tails is not within scope of IEE regs and is down to DNO, advice in this document has been generally accepted by all.
 11 June 2010 12:37 AM
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spinlondon

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I think that you may want to consider Appendix 4. Especially voltage drop
 11 June 2010 10:40 AM
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slittle

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Originally posted by: chevalier

Have a look at Electrician FAQ which gives advice in these situations. The length of meter tails is not within scope of IEE regs and is down to DNO, advice in this document has been generally accepted by all.



Thanks, a really useful document, at least if they play up we've now got a document to quote from and beat the suppliers with.

This is obviously the output from the consultation that sort to give electricians permission to pull fuses, not the ultimate answer but better than we had I think.

Stu
 11 June 2010 03:54 PM
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Dale76uk

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My dealings with edf of late tell me that there needs to be an means of isolation within 3m of the meter. Luckily it was a new build so they fitted the dp isolator and I ran the tails a further 7m. :-)
 11 June 2010 03:57 PM
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AJJewsbury

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My dealings with edf of late tell me that there needs to be an means of isolation within 3m of the meter. Luckily it was a new build so they fitted the dp isolator and I ran the tails a further 7m. :-)

Are you sure that isolation alone is sufficient? - most seem to want the customer to take responsibility for overcurrent protection too (as the DNO can't control Zs relating to their fuse if they allow unlimited "tail" length before the next stage of overcurrent protection).
- Andy.
 11 June 2010 04:14 PM
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alancapon

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Originally posted by: Dale76uk
My dealings with edf of late tell me that there needs to be an means of isolation within 3m of the meter. Luckily it was a new build so they fitted the dp isolator and I ran the tails a further 7m. :-)

That would get a "danger notice" from me if I spotted it here. Within 3m cable distance of the electricity meter (or whatever figure the DNO use - we use 2.500m), there must be overcurrent protection. An isolator is not good enough. For a new-build, we would refuse to connect the supply.


Regards,

Alan.
 11 June 2010 08:08 PM
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jcm256

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Alan,
Could you clear this up please, I was under the impression that there is no need to duplicate provided the tails were of adequate size the cut out fuse or fuses could be used for protection for any length of tails, over 2 meters (within reason of course) most older larger installations installed to a early addition can have branching tails from isco connectors to distribution equipment all over the board. Provided the conductors are erected in such a manner that the risk of short-circuit fire, or danger to persons is not an issue would this older type of installation be not now in order.


This one (EDF) extract from web site below only mentions isolation does not state protective devices.

Installing meter tails
For 100 amp cut-outs, one set of 25mm double-insulated (brown/brown and blue/blue) meter tails must be installed
ready for connection into the meter.
Meter tails should normally be no more than 2m in length. If slightly longer, they must be adequately supported
and protected from damage as necessary. Meter tails must not be installed inside the cavity walls of buildings.
Where the consumer unit is remote from the meter position, the electrician must install a suitable sub-main cable
together with means of isolation. All work must be carried out in accordance with the current edition of BS7671.
EDF Energy Networks or our appointed meter operators will not install SWA cables into any metering equipment.
Only 25mm double-insulated (brown/brown and blue/blue) tails must be left for the final connection into the meter.


http://www.edfenergy.com/produ..._RESPONSIBILITIES.pdf

Regards
jcm
 11 June 2010 09:00 PM
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dg66

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There is no main switch for the whole installation.

Look up the definition of installation, it doesnt mean building.The four boards you're describing could be deemed to be four installations.

-------------------------
Regards

Dave(not Cockburn)

Edited: 12 June 2010 at 11:41 PM by dg66
 11 June 2010 09:08 PM
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alancapon

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My employers rules state 2.500m. BS7671:2008 regulation 433.2.2 says 3m. In the supplier's case, the cutout fuse installed will always be able to protect 3m of 25mm tails (assuming we are talking max 100A up to three phases). There is a possibility that it might protect further, depending on design (materials, installation method etc). The problem is that the supplier does not have the time to carry out the calculation for each property. As BS7671:2008 gives a distance, most suppliers use something around this value for what their fuse will cope with. At this point, the customer must have overcurrent protection that is rated for the design of the submain, whether it grades with the cutout fuse or not.

Although the document you mention does not state that overcurrent protection is required after the 2m of meter tails, I would expect to find it in EDF's conditions of connection.

Regards,

Alan.
 11 June 2010 11:01 PM
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chevalier

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Stu - yes you are quite correct, this FAQ/Guidance document was the result of the DCUSA consultation. From the comments fed back it was clear that the electricity industry had not effectivily communicated how it was 'meant to work' so this is intended to assist. There is further to go in ensuring all staff are aware and operate in this way, but you have to start rebuilding somewhere!
 12 June 2010 10:43 AM
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Backintime

Posts: 282
Joined: 11 April 2007

Alan is correct. Remember local requirements override BS7671 especially the connection requirements specified by the DNO. Hence when the meter tails exceed the length stipulated by the DNO, it would be acceptable to put in a switchfuse or MCCB to provide overcurrent protection for the 3m+ meter tail. The DNO will normally, IMO, give their consent even if there is no grading between your device and the cut-out fuse - you have done the best you can already.

Regards

Marty
 15 June 2010 02:22 PM
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AJJewsbury

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Could you clear this up please, I was under the impression that there is no need to duplicate provided the tails were of adequate size the cut out fuse or fuses could be used for protection for any length of tails, over 2 meters

What Zs would you need for "adequate protection" of 25/16 tails with a 100A BS 1361? And what do the DNO usually quote for Ze for TN-S and TN-C-S?
- Andy.
 15 June 2010 03:29 PM
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JonSteward

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From EDF
Installing meter tails
For 100 amp cut-outs, one set of 25mm double-insulated (brown/brown and blue/blue) meter tails must be installed
ready for connection into the meter.
Meter tails should normally be no more than 2m in length. If slightly longer, they must be adequately supported
and protected from damage as necessary. Meter tails must not be installed inside the cavity walls of buildings.
Where the consumer unit is remote from the meter position, the electrician must install a suitable sub-main cable
together with means of isolation. All work must be carried out in accordance with the current edition of BS7671.
EDF Energy Networks or our appointed meter operators will not install SWA cables into any metering equipment.
Only 25mm double-insulated (brown/brown and blue/blue) tails must be left for the final connection into the meter.
 15 June 2010 05:55 PM
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jcm256

Posts: 1839
Joined: 01 April 2006

To AJ Jewsbury,
I know what you are saying but surly if Ze was high it would not matter if the tails were 3 meters or a bit more, provided the tails were of adequate size. For the tails could you not intrepid from the 17th chapter 43 or even 433.3.1 wording relating to duplicate protection devices.
There is a sort of brown field site zombie land out there and that's where I will dwell on this one.
Here is the site below: (another one from EDF)

http://www.eon-uk.com/distribution/1210.aspx

jcm
 16 June 2010 01:52 PM
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AJJewsbury

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I know what you are saying but surly if Ze was high it would not matter if the tails were 3 meters or a bit more, provided the tails were of adequate size.

It depends on what you mean by "adequate". Protected against overload is one thing, against faults is another. A 100A BS 1361 needs Zs below 0.365 ohms to disconnect within 5s - if Ze was 0.35 ohms it only takes a few metres of tails to push it over the limit. There's 434.3 to consider as well as 433.3.1 and the stumbling point will be the supplier's/distributors's agreement - and it seems that usually depends on a 3m (or thereabouts) limit. From their point of view they perhaps need to consider future changes - they may need to increase supply capacity (not so long ago 60A was considered the max for domestic, now it's 80A or 100A) and if they have to uprate their fuse they'd need to be able to check that they're not creating a hazard in doing so - checking that a couple of metres of (mostly) visible tails is one thing - checking 10s of metres of "tails" buried through various bits of building fabric might be another...

- Andy.
 16 June 2010 01:59 PM
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leonardsmalls

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Joined: 07 July 2008

I've got a similar job next week where a meter is being moved 8m away from the C.U.
I haven't had any joy from Central Networks on their policy, so I'm assuming that I'll have to fit a 100A switch fuse to protect the tails/sub-main...
And I'm also assuming I'd be best off using SWA as it goes through a study and into a garage.
Any thoughts?
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