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Topic Title: CU upgrade - 16mm tails embedded in the wall
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Created On: 02 March 2013 06:23 PM
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 02 March 2013 06:23 PM
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Rum1

Posts: 127
Joined: 13 February 2009

Just thought i'd seek a few opinions (as i like to do)

Been to see a couple of customers locally - on the same street actually who want a fuse board upgrade.

Both old 60A wylex fuse boards are supply by 16mm tails/ 16mm earths. They are TN-C-S. 10mm bonds in place etc. Properties circa 1985.

Point one is that the tails come through into the hall ways and are embedded under the plaster under large plastic capping. So the tails are less than 50mm in the wall without RCD protection. How does this work with the 17th Edition requirements?

Point 2 is that i usually always ungrade tails to 25mm etc as usually not a problem. To upgrade these tails will mean either chopping out walls in nicely decorated hall ways (if you can do this under the 17th edition?)or having chunky trunking straight down the hall wall instead - won't look nice.
I was wondering if i might leave the 16mm tails in place and reuse.
I have not actually taken the main service fuses out to check value but would they could be anything from 60A, 80A, 100A - but would the supplier have put 100A in on 16mm tails anyway? All looks original.

One house has a lowish loading really (60A max maybe : 1x ring, 1x cooker, 2x lights, Immersion) but one of these houses has an electric shower (8.5mm max) on top thats been added so total load could be creeping over 80A.
I guess it all comes down to the cut out fuse values? But not possible to see at quoting stage. Most service heads just marked as 100A or cannot be seen.

To what extent do you leave the 16mm tails in place when so disruptive/awkward/unsightly to replace during an upgrade?

Just interested in how others approach issues with tails
 02 March 2013 06:27 PM
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geoffsd

Posts: 258
Joined: 15 June 2010

Nothing wrong with them.as they are there already,

I don't understand the obsession with 'upgrading' to 25.
 02 March 2013 06:38 PM
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daveparry1

Posts: 5877
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Agreed Geoff, it just depends on the expected maximum load, 16mm is adequate in most cases, 16mm is good for 87 amps in free air, I know in this case they're plasrered in but still not a problem in my opinion,

Dave.
 02 March 2013 06:39 PM
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Rum1

Posts: 127
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If it turns out there are 100A service cut out fuses - then i would have thought 25mm tails required?
What about re-embedding them in wall if customer doesn't want trunking in middle of hall wall? Just wondered about 17th edition when it comes to tails as well?
 02 March 2013 06:58 PM
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alanblaby

Posts: 283
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They really need mechanical protection if there is not an upfront RCD.
I very nearly drilled through a 25mm tail embedded in a wall a few weeks ago, of course, they were at an angle, but I really should have tried to trace their run before drilling.
It looked like the utility room there were in had recently been tiled, so the tiler had just unclipped them and buried them where he could fit them easily.
 02 March 2013 07:12 PM
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Rum1

Posts: 127
Joined: 13 February 2009

Thanks for replies.

The only mechanical protection for these tails looks like plastic capping and this estate has all the tails embedded since first installed. You can't put an RCD at the meters otherwise whole installation will be vunerable to one RCD tripping - again something the 17th edition won't allow as i understand it (One fault and you'll loose all power if said RCD trips - hence why we have at least dual RCD consumer units now).

So RCD not allowed to protect tails and what classes as mechanical protection to these tails?
 02 March 2013 07:15 PM
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daveparry1

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If it turns out there are 100A service cut out fuses

Not necessarily Rum1, it depends on the loading as I said earlier, I agree they should either be exposed or protected though. If you're not replacing them put a note on the EIC in the "comments on existing installation" box,

Dave.
 02 March 2013 07:17 PM
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alanblaby

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3mm steel plate, or similar.
I don't know why you think one RCD cannot be used?
It's all about inconvenience, so if necessary, one (30mA) RCD can still be used if the installation is suitable for that use.
How about a 300mA RCD upfront?
That would be far better than having unprotected buried cables.
I suppose it is all down to what the customer wants, but you will have to note on the EIC that the cables are unprotected and a potential danger.
 02 March 2013 07:34 PM
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Rum1

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Take your point Dave about it depending on the load.

Alan would the upfront 300mA RCD be time delayed? Would the 30mA RCD's in the consumer trip first if not?

Fancy the flippin builders putting the tails in the wall in the first place!!
 02 March 2013 07:43 PM
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daveparry1

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You shouldn't be surprised at anything builders do where electrics are concerned Rum1 !
 02 March 2013 07:52 PM
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Rum1

Posts: 127
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I can imagine though that the builders sparkies defence could be that the tails are in line beneath the fuse box and so in theory are in a "Safe Zone" so met the regs of the day. Not ideal but i guess that would be true
 02 March 2013 08:01 PM
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daveparry1

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Yes it was ok before all the sillyness of the 17th edition came in.
 04 March 2013 02:38 PM
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AJJewsbury

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How about a 300mA RCD upfront?
That would be far better than having unprotected buried cables.

Not much use for additional protection. The human body (when dry) will have a resistance in the region of a couple of thousand Ohms - so will limit the 'fault' current to a level where a 300mA RCD probably won't trip at all - let alone within 40ms.
- Andy.
 04 March 2013 03:35 PM
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normcall

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Just remember in the mid 80's (been there, did it!) the electricity boards tended to accept anything, just to get a connection.
I spent a year being an inspector and I can remember turning a whole swath of new homes down because only 10mm to the MET and 6mm bonding on a PME service.
All contractors had been notified that all connections after April 1st had to comply with the 16+10 requirement - no matter how long the contract had been running. It seems I was the only one in the depot who actually knew (teach my wife to tell me to get a proper job!). Just one of several altercations I had before they came to the conclusion that I didn't fit. (what a surprise)

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Norman
 04 March 2013 04:08 PM
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Rum1

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So an upfront RCD to protect the tails embedded in the plaster to comply with 17th is not so straight forward then? Therefore cables will have to be on show inside or out - in trunking or something...don't think that will go down well with customers ...what a pain.

Normcall....i have had a role as an inspector...in that time never discovered tails embedded in masonary so a new one on me at present. However i can fully appreciate what you are saying...alot of these companies just want someone to sign the paperwork in double quick time..just the same today as yester-year, but thats another story...
 04 March 2013 04:52 PM
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AJJewsbury

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So an upfront RCD to protect the tails embedded in the plaster to comply with 17th is not so straight forward then? Therefore cables will have to be on show inside or out - in trunking or something...don't think that will go down well with customers ...what a pain.

Not necessarily - BS 7671 gives a number of options - something with a concentric c.p.c. - e.g. SWA - would be fine without 30mA RCD protection.
- Andy.
 04 March 2013 04:59 PM
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OMS

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You're changing the DB - unless those tails are scorched and blackened you aren't adding any new load - so 16mm2 is almost certainly not an issue

In the same way that you would comment on problems or departures on outgoing circuits, all you need to do is comment on departures and observations on incoming circuits - so a lack of 30mA RCD protection on buried tails is just that.

Just explain the situation to your client indicating where what they have deviates from current thinking, give them the options in the form of a menu - let them decide and then just crack on.

How long are they out of interest - and what's the source end protection

Regards

OMS

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Failure is always an option
 04 March 2013 05:02 PM
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aligarjon

Posts: 2726
Joined: 09 September 2005

Why change it ? There is no sign of overload damage to the tails. You haven't installed them they are existing. i would give the customer the option at least. A note on the cetificate and maybe a warning label on the CU would be good incase someone decides to fit a coat hook under neath.
Just get the main fuse downgraded if its 100amp if you're that worried.


Gary

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Specialised Subject. The Bleedin Obvious. John Cleese
 04 March 2013 09:10 PM
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BrucieBonus

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Regarding the concealed cables - The ideal option would be to replace with say SWA (or even tails run in trunking) - no need for RCD then. BUT in my view (and NICEIC, as I checked) as long as you make a note then OK to go ahead without making any change to the tails - unless of course the customer wants the gold standard option
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