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Topic Title: Sub-main notifiable?
Topic Summary: Supply cable/meter move
Created On: 03 November 2013 07:03 AM
Status: Post and Reply
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 03 November 2013 07:03 AM
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normcall

Posts: 8111
Joined: 15 January 2005

Just doing an estimate to provide a new sub-main as customer having extension built where the outside box is at the moment.
At the moment I've found a nice 100mA RCD protecting 16mm tails buried in the wall, into a black DP block feeding two old Wylex CSUs.
I'm proposing trunking with 25mm tails surface mounted for about 6 metres. 100A DP switch at CU end and 100A switchfuse with 100A 30mA RCD and earthing via a new road.
The REC have requested a test certificate which then got me thinking as to whether it's a new circuit and thus notifiable or replacement/improvement which might not.
As I don't do many of these, someone out there must do and provide a quick answer.

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Norman
 03 November 2013 09:39 AM
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John Peckham

Posts: 7375
Joined: 23 April 2005

Norm

I am assuming this installation is TT reading between the lines of your post? I would take the tails from the meter in to a 100mA time delayed RCD in a plastic enclosure then tails from the RCD into a 100A switch fuse to supply your new distribution circuit. At the far end of the distribution circuit I would fit a dual RCD board to supply the final circuits in the house. I may not choose singles in trunking unless I already had some spare 25mm singles and 6m trunking in stock. I would probably go for 25mm 2 core SWA as it is quicker to install and more robust.

Norm to help you with the modern speak so as to impress the boys at the trade counter sub mains are called distribution circuits now and RECs are called DNOs.

It is definitely a new circuit so the work is notifiable for Part P.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 03 November 2013 10:17 AM
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normcall

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Joined: 15 January 2005

You are making more difficult than it is.
It seems just a 100mA RCD is protecting 16mm tails from an outside box chased into the wall down one side of a small room. Naturally just the main fuse as protection.
The meter and supply is going to be relocated inside and the DNO (see I catch on quick(ish)) have asked for 25mm tails and 16mm earth protection cable (earth wire) to be presented to them as I suspect they want to TN-C it.
Just to tidy everything I'm going to install 50mm (2") PVC trunking with a pair of 25mm tails complete with 16mm G/Y round the wall at high level to the existing mess (not helped by solar panels installed) terminating with 100A DP switch for easy connection to existing tails.
The new mains position will just have a 100A DP switch fuse (to protect the 5m long tails) and 100A 30mA RCD complete with earthing rod and 10mm (feeling really generous) from rod to block connecting to the 16mm off to the fuseboxes (or whatever europe wants to call them).
I have suggested to the customer that the existing assortment of problems is left to whoever is doing the extension (eg a couple of 2.5mm 6242Y sprouting out the wall which feed the new kitchen - less any g/y sleeving to the protective conductors, let along the sheath actually get as far as one fusebox. Ditto shower circuit etc. etc.

Why is everything so difficult? Why would you suggest meter to RCD then switch fuse? This modern thinking is too complicated so I'll still go for meter to switch fuse to RCD. That way is the client goes for rcbo's, then the RCD can be replaced with a time delay 100mA 100A easily to provide a degree of separation.

Anyway, I'll tell him that he will need to keep the local council in work a bit longer.

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Norman
 03 November 2013 10:18 AM
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daveparry1

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I had this discussion with niceic help line about three years ago and the consensus was that it wasn't notifiable, not sure why we came to that conclusion because as John says it is a new circuit.
As a second thought though I suppose we we could say it's an addition to a circuit because it's being fed from the same place just like adding another cable to an mcb in a consumer unit?

Dave.
 03 November 2013 10:36 AM
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normcall

Posts: 8111
Joined: 15 January 2005

That was my initial view as well, but thinking is bad for me and doubt started to creep in.
Basically it's just replacing something that already exists and actually correcting errors (tails just buried in the plaster,I'm sure that' not right and just the main fuse as protection (OK, 100mA RCD which I suspect was the result of the common error of believing it's also overload protection).
I'll see if we have any other views and I might waste my time contacting our local building control tomorrow (blind leading the blind and all that!).

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Norman
 03 November 2013 11:01 AM
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John Peckham

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Norm


You did not mention the meter was shifting from the existing supply position. I would ask/sort out what sort of earthing system the final job is going to be as you there is no need for an RCD if it is not going to be TT. I assumed as you had mentioned a rod (road sic) it was TT if it is not why the RCD? Also if it is not going to be TT why the rod?

If the meter position is moving down here in UKPN land they would want a double pole isolator at the head with their fuses protecting the tails. Depending on who comes to site to survey the job from the DNO sometimes they require a switch fuse at the supply end. Then at the new position a Series 7 with a red head carrier before the meter so there is a facility for isolation for meter changes. Then in to your board with the tails from the meter.

Also down here in UKPN land they will not re-connect to the existing installation without a satisfactory EICR or an EIC if new, that includes key meters if there has been a change of occupier sometimes.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 03 November 2013 03:56 PM
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normcall

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John
It's currently TT and the customer is quiet happy with that.
All the UKPN have left is a requirement for a pair of 25mm tails and 16mm earth wire. They also wanted a test certificate complying with BS7671.
Thereby lies the problem. If it's a new circuit (even if just replacing existing although with a different start starting point), then the circuit goes from my new 100A switch fuse , earth protection by a 30mA RCD with a rod and finishing with a 100A DP switch. Certificate issued for new circuit.
OTOH, at the meter is only moving about 2m from outside to inside, then I would have to issue a report on the condition of the existing installation. My way surely is the most practical (how stupid can you get) rather than leave something with no overload, tails buried just under the plaster and 100mA RCD.
I can imagine that was what whoever came to see the job thought would happen and obviously want a certificate. My way has a nice safe circuit no different to any other waiting for an appliance to be installed (only in this case a couple of existing fuseboxes and in use for many years).
I have done this a couple of times in the past and had no problems even to the extent they just provided a 100A DP switch and left me to sort out any unforeseen problems, which naturally there were not.

I'm sure I said the service and meter were being moved from outside to inside, so I don't think a red cutout etc will apply. Nothing else is changing (apart from correcting the 100mA and buried tails) at the moment - even the overhead cable is just being cut back, the same meter although they seem to want to provide an earthing facility.

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Norman
 03 November 2013 04:44 PM
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John Peckham

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Norm

If you are unsure if the DNO are going to provide you with an earth then I would go with the worst case scenario and fit a 100mA time delayed RCD in a plastic enclosure after the supply head and a 100A switch fuse at the supply end. That way you cannot be wrong with both overload and earth fault protection for your new distribution circuit. If the earthing system is changed to TN-C-S then you still have a compliant installation with a bit of extra earth fault protection.

If you are certain the DNO is going to supply an earth you will not need the RCD. If you are certain that the DNO will not want additional overload protection for the distribution circuit then just fit a REC isolator. The danger is the DNO person turning up on site may have a different view of what his/her company policy is to the person who surveyed the job and may refuse to connect.

I would not most certainly fit a 30mA RCD for the whole installation as there would be a high risk of nuisance tripping and it would not in my view be compliant with regulations 314.1 and 531.2.4.

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John Peckham

http://www.astutetechnicalservices.co.uk/
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