Hi,

The House renovation plans progress... I've been examining possibilities for
siting the new CU I'll be installing (which will be BNA'd along with 6
million other notifiable small works). Been busy reading up on the 17th and
testing procedures in readiness.

Part of this may involve asking EDF to install a supply isolator and move
the tails.

I heard a rumour that EDF are in the habit of asking for an EIC *signed by a
member of one of the approved bodies*.

Seeing as an EIC is required for alterations and changes which exceed minor
works, and an EIC can only be signed by the relevant designer, installer
and tester (ie noone else apart from me, with the possible exception of the
tester) - doesn't this rather contradict Part P notifiable work via the
Building Control route?

I don't have any problem providing an EIC as an unqualified person (in fact
it is becoming a point of pride to make sure I do everything correctly to
the 17th), but if EDF won't accept it and no-one else can do it, then I'm
stuffed.

Anyone had any experience of EDF moving or reconnecting the supply under
similar circumstances?

It sounds like nonsense in principle as what happens if there is a sound
supply but no EIC (so more than half the properties in England I imagine)?

There are work-arounds...

1) I could work live on the existing henley block. It's not something that
fills me with joy though having seen pictures of burns victims. But I
wouldn't have to involve EDF. However, apart from it being inadvisable, the
henley block is in a less than ideal location.

2) Pay a NICEIC/etc sparks to wire up a CU with one 20A radial "site
supply". Not so daft, as I'll be working of a site supply initially until I
get all the old cabling stripped and walls chased. But it gauls me as I've
already paid the BCO the BNA fee.

3) Be naughty and pull the DNO's fuse. That however gives EDF an excuse to
get involved and I still have the issues in (1) regarding the henley block.

Any advice before I open the can of worms by phoning their networks division
on Monday?

Many thanks,

Tim

> Anyone had any experience of EDF moving or reconnecting the supply under
> similar circumstances?

Yes, they didn't even glance at the certificate.

If your installation looks right then I think that's what you can
expect, if it looks odd the expect rules an regulations.

On 18 Jul,  
     Tim S  wrote:

> 3) Be naughty and pull the DNO's fuse. 

That's what I did. Shortly afterwards the meter was replaced (as it had been
in for 15 years -- was new in 1954) with a digital one, and the fuse was
re-sealed. No comment was made.
 
-- 
  B Thumbs
  Change lycos to yahoo to reply

On 18 Jul, 19:43, Tim S  wrote:
> Hi,
>
> The House renovation plans progress... I've been examining possibilities for
> siting the new CU I'll be installing (which will be BNA'd along with 6
> million other notifiable small works). Been busy reading up on the 17th and
> testing procedures in readiness.
>
> Part of this may involve asking EDF to install a supply isolator and move
> the tails.
>
> I heard a rumour that EDF are in the habit of asking for an EIC *signed by a
> member of one of the approved bodies*.
>
> Seeing as an EIC is required for alterations and changes which exceed minor
> works, and an EIC can only be signed by the relevant designer, installer
> and tester (ie noone else apart from me, with the possible exception of the
> tester) - doesn't this rather contradict Part P notifiable work via the
> Building Control route?
>
> I don't have any problem providing an EIC as an unqualified person (in fact
> it is becoming a point of pride to make sure I do everything correctly to
> the 17th), but if EDF won't accept it and no-one else can do it, then I'm
> stuffed.
>
> Anyone had any experience of EDF moving or reconnecting the supply under
> similar circumstances?
>
> It sounds like nonsense in principle as what happens if there is a sound
> supply but no EIC (so more than half the properties in England I imagine)?
>
> There are work-arounds...
>
> 1) I could work live on the existing henley block. It's not something that
> fills me with joy though having seen pictures of burns victims. But I
> wouldn't have to involve EDF. However, apart from it being inadvisable, the
> henley block is in a less than ideal location.
>
> 2) Pay a NICEIC/etc sparks to wire up a CU with one 20A radial "site
> supply". Not so daft, as I'll be working of a site supply initially until I
> get all the old cabling stripped and walls chased. But it gauls me as I've
> already paid the BCO the BNA fee.
>
> 3) Be naughty and pull the DNO's fuse. That however gives EDF an excuse to
> get involved and I still have the issues in (1) regarding the henley block.
>
> Any advice before I open the can of worms by phoning their networks division
> on Monday?
>
> Many thanks,
>
> Tim

I just pulled the fuse to change the tails from my meter to the CU. No
meter reader has ever commented, and I don't think it's been re-sealed
in 5 years.

To be honest, I don't think they care if you mess with the fuse /
seals on the meter connections. Now if you mess with the seals on the
meter *case* that's a different matter. There's no legitimate reason
to do that.

Jon.

In article
,
   Tournifreak  wrote:
> To be honest, I don't think they care if you mess with the fuse /
> seals on the meter connections. Now if you mess with the seals on the
> meter *case* that's a different matter. There's no legitimate reason
> to do that.

There is if installing a new CU and the tails ain't long enough.

I think the supplier would look at extremely low usage before taking any
action if they saw seals tampered with and suspected dishonesty. The types
who do this aren't going to be satisfied with a normal size bill. ;-)

-- 
*Welcome to Shit Creek - sorry, we're out of paddles*

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Dave Plowman (News) coughed up some electrons that declared:

> In article
> ,
>    Tournifreak  wrote:
>> To be honest, I don't think they care if you mess with the fuse /
>> seals on the meter connections. Now if you mess with the seals on the
>> meter *case* that's a different matter. There's no legitimate reason
>> to do that.
> 
> There is if installing a new CU and the tails ain't long enough.
> 
> I think the supplier would look at extremely low usage before taking any
> action if they saw seals tampered with and suspected dishonesty. The types
> who do this aren't going to be satisfied with a normal size bill. ;-)
> 

Thanks for the replies so far. Having looked at the model EIC in the back of
the 17th, it's not going to be hard to complete one in an unqualified way,
especially if it has one final circuit comprising 20 radial to a double
socket!

I'll do an EIC for the final installation, but unless I've managed to gain a
2392 by then, I'll just attach the PIR that BC arranges to it as
verification of testing.

I'm looking out for a multifunction tester presently.

We'll see what they say when I ring EDF's networks division on Monday.

Not too happy breaking seals as it gives them an excuse to be difficult
later, but if it transpires that they're going to be difficult anyway, I'll
probably live-work to the current henley, very very carefully with
appropriate precautions. So much for safety... The state of this country is
serious starting to annoy me.

I'll post their initial response back here.

Cheers

Tim

On Sat, 19 Jul 2008 12:14:16 +0100, Tim S wrote:

> I'm looking out for a multifunction tester presently.

If you're buying new I'm quite happy with my Dilog which was significantly
cheaper than the Fluke and Megger equivalents, does what it says on the
tin, is calibrated (though the calibration tolerances are enough to drive
a coach and horses through so it's no precision instrument) and comes with
a free one/two-probe tester which I've seen badged by Fluke for best
part of ton elsewhere.


-- 
John Stumbles

87.5% of statistics are made up

Tim S wrote:

> Thanks for the replies so far. Having looked at the model EIC in the back of
> the 17th, it's not going to be hard to complete one in an unqualified way,
> especially if it has one final circuit comprising 20 radial to a double
> socket!

Temporary supply?  You do know that they won't give you PME for that? 
It will need to be TT'd.

And that the IEE/T have downloadable forms:
http://www.theiet.org/publishing/wiring-regulations/forms/

-- 
Andy

Andy Wade coughed up some electrons that declared:

> Tim S wrote:
> 
>> Thanks for the replies so far. Having looked at the model EIC in the back
>> of the 17th, it's not going to be hard to complete one in an unqualified
>> way, especially if it has one final circuit comprising 20 radial to a
>> double socket!
> 
> Temporary supply?  You do know that they won't give you PME for that?
> It will need to be TT'd.

Do you know the reasoning - it seems non obvious?

Basically, the plan started as having the new CU in the correct place,
fitted with incomer and one or two RCBOs, from which a temporary (in the
common use of the word) fixed installation was made feeding literally one
or two 13A outlets via surface clipped T&E to run power tools.

All the chasing and box sinking would be done in one hit, then each final
circuit would be added. As soon as the ground socket ring was completed,
the temporary RCBOs would come out and the ways used for permanent
circuits.

Does this class as "temporary" in the context?

In the worst case, I can use the current CU to distribute a couple of
temporary circuits, and have the new CU ready with at least a couple of
permanent final circuits (most sockets and lighting downstairs), but I was
hoping to clear out all the old crap at the start of the job.

> 
> And that the IEE/T have downloadable forms:
> http://www.theiet.org/publishing/wiring-regulations/forms/
> 

Thanks - I did know the IET had them somewhere on their website, so thanks
for the link.

Cheers

Tim

Tim S coughed up some electrons that declared:

> Andy Wade coughed up some electrons that declared:
> 
>> Tim S wrote:
>> 
>>> Thanks for the replies so far. Having looked at the model EIC in the
>>> back of the 17th, it's not going to be hard to complete one in an
>>> unqualified way, especially if it has one final circuit comprising 20
>>> radial to a double socket!
>> 
>> Temporary supply?  You do know that they won't give you PME for that?
>> It will need to be TT'd.
> 
> Do you know the reasoning - it seems non obvious?
> 

Forget that bollocks, it's late and I drank beer and typed without reading.

PME as in TN-C-S, then I presume the reason is the same as no PME to
outbuildings: certain supply faults may produce significant PD between the
PME earth and local true earth. I can see that being an issue with a site
supply, in the usual sense of the word, ie a muddy field full of builders
and building going up.

This would be a minimal fixed installation with a short expected lifetime in
an established dry building.

This is one of the things I have to check - I'm hoping it's a *good* TN-S
system (it's not overhead wires, so I have a chance, but supply head was
replaced 10 years back and I've heard EDF like TN-C-S). A good question to
put to EDF on Monday.

Cheers

Tim

John Stumbles coughed up some electrons that declared:

> On Sat, 19 Jul 2008 12:14:16 +0100, Tim S wrote:
> 
>> I'm looking out for a multifunction tester presently.
> 
> If you're buying new I'm quite happy with my Dilog which was significantly
> cheaper than the Fluke and Megger equivalents, does what it says on the
> tin, is calibrated (though the calibration tolerances are enough to drive
> a coach and horses through so it's no precision instrument) and comes with
> a free one/two-probe tester which I've seen badged by Fluke for best
> part of ton elsewhere.
> 
> 

This one?

http://www.tlc-direct.co.uk/Products/TM9083P.html

Unfortunately dilog's website is partly knackered so I can't download the
manual (if I could anyway).

Do you recall if the supplied test leads are fused?

The freebie volt tester is worth having. It's on TLC's website so I'll nip
into my local branch and see if they have one I can look at.

Cheers

Tim

Tim S wrote:

> PME as in TN-C-S, then I presume the reason is the same as no PME to
> outbuildings: certain supply faults may produce significant PD between the
> PME earth and local true earth. I can see that being an issue with a site
> supply, in the usual sense of the word, ie a muddy field full of builders
> and building going up.

And - key point - no main bonding present, possibly because the water 
and gas pipes aren't yet in place.  I guess that if you have the main 
services bonded and aren't going to disturb them then they should be 
able to give you a TN-x earth, even though the final circuit 
arrangements are temporary.  You'll have to ask them, but don't be 
surprised if they say "no, it must be TT" because what you're proposing 
isn't on their standard menu of supply types.

In any case it's no big deal.  When I re-wired here I knocked up a 
temporary supply board - four old surface mount double sockets, a 1-way 
Wylex switch-fuse with 30 A fuse and a 30 mA RCD.  The temporary earth 
was a length of 22 mm water pipe bashed in the ground and brought in via 
a hole drilled in a wooden window frame.  Eastern Electricity, as then 
was, were quite happy to connect this.  As rewiring proceeded I 
temporarily teed off the temporary tails to feed the new CU.  When ready 
for proper connection of the new tails I removed the makeshift feed 
arrangement, left my test equipment lying conspicuously about and called 
out 'the board' again.  They connected the new installation up, 
including TN-S earth, with no quibbles or awkward questions at all.

-- 
Andy

On Jul 20, 2:53 am, Tim S  wrote:
> http://www.tlc-direct.co.uk/Products/TM9083P.html

That is 383各.
I would also look at the Megger MFT 1552 for about 60 more,
it is well regarded and might have a better resale value later.


> Do you recall if the supplied test leads are fused?

Fused test leads are worth it, and typically quite expensive.

Alternatively, you could hire a meter when ready and spend
the saving on going all RCBOs or a triple RCD wide CU.
--
DB.

Andy Wade coughed up some electrons that declared:

> Tim S wrote:
> 
>> PME as in TN-C-S, then I presume the reason is the same as no PME to
>> outbuildings: certain supply faults may produce significant PD between
>> the PME earth and local true earth. I can see that being an issue with a
>> site supply, in the usual sense of the word, ie a muddy field full of
>> builders and building going up.
> 
> And - key point - no main bonding present, possibly because the water
> and gas pipes aren't yet in place.  I guess that if you have the main
> services bonded and aren't going to disturb them then they should be
> able to give you a TN-x earth, even though the final circuit
> arrangements are temporary.  You'll have to ask them, but don't be
> surprised if they say "no, it must be TT" because what you're proposing
> isn't on their standard menu of supply types.
> 
> In any case it's no big deal.  When I re-wired here I knocked up a
> temporary supply board - four old surface mount double sockets, a 1-way
> Wylex switch-fuse with 30 A fuse and a 30 mA RCD.  The temporary earth
> was a length of 22 mm water pipe bashed in the ground and brought in via
> a hole drilled in a wooden window frame.  Eastern Electricity, as then
> was, were quite happy to connect this.  As rewiring proceeded I
> temporarily teed off the temporary tails to feed the new CU.  When ready
> for proper connection of the new tails I removed the makeshift feed
> arrangement, left my test equipment lying conspicuously about and called
> out 'the board' again.  They connected the new installation up,
> including TN-S earth, with no quibbles or awkward questions at all.
> 

Thanks Andy. Round at the house again today. Strewth, the state of the
wiring in the roof spaces - mice have been busy, not surprised the lighting
circuit failed given various bits of 1mm and 1.5mm that have been munched
through. Yes the relevant fuses are removed...

I digress... A third option would be to have the CU by the front door, where
the wall sets back 20mm and build a wiring cupboard to enclose it. Get EDF
to relocate the supply head and meter there. I'll ask them how much that'll
be (not cheap I know) but looking like an elegant solution. People expect
CU's in halls, the ceiling accesses probably the best bit of roof void for
wiring and a floor-ceiling wiring cupboard would leave plenty of room for
SWA termination, from cables going outside. I'd put a duct in leading to a
pit outside for future expansion.

Ah, the endless choices available when fixing a knackered house.[1]

Couple of questions:

1 Are there any issues with a main bond around 15 meters long to reach the
gas and water incoming services from the proposed MET position? I assume it
is sized to achieve a certain impedance? (Haven't got that far through the
wiring regs yet).

2 Are there any restrictions on the flammability of a board the CU +
accessories are fixed to. I was thinking of lining the back of such a
cupboard with ply? I know there is an issue with old open backed equipment.

BTW, did you bother with a 100mA time-delayed RCCB for your temporary TT
system (bit pointless with a single final circuit I know).

Cheers

Tim

[1] On the plus side, SWMBO and I thrashed out the design mods to the rest
of the house this afternoon. Practically ready to see the BCO now, who was
most amenable to a personal chat pre-BNA when I spoke to him last week.
Interesting to see if he puts the kibosh on any of our plans...

On Fri, 18 Jul 2008 20:43:38 +0100, Tim S wrote:

> Hi,
> 
> The House renovation plans progress... I've been examining possibilities
> for siting the new CU I'll be installing (which will be BNA'd along with
> 6 million other notifiable small works). Been busy reading up on the
> 17th and testing procedures in readiness.
> 
> Part of this may involve asking EDF to install a supply isolator and
> move the tails.
> 
> I heard a rumour that EDF are in the habit of asking for an EIC *signed
> by a member of one of the approved bodies*.
> 
> Seeing as an EIC is required for alterations and changes which exceed
> minor works, and an EIC can only be signed by the relevant designer,
> installer and tester (ie noone else apart from me, with the possible
> exception of the tester) - doesn't this rather contradict Part P
> notifiable work via the Building Control route?
> 
> I don't have any problem providing an EIC as an unqualified person (in
> fact it is becoming a point of pride to make sure I do everything
> correctly to the 17th), but if EDF won't accept it and no-one else can
> do it, then I'm stuffed.
> 
> Anyone had any experience of EDF moving or reconnecting the supply under
> similar circumstances?
> 
> It sounds like nonsense in principle as what happens if there is a sound
> supply but no EIC (so more than half the properties in England I
> imagine)?
> 
> There are work-arounds...
> 
> 1) I could work live on the existing henley block. It's not something
> that fills me with joy though having seen pictures of burns victims. But
> I wouldn't have to involve EDF. However, apart from it being
> inadvisable, the henley block is in a less than ideal location.
> 
> 2) Pay a NICEIC/etc sparks to wire up a CU with one 20A radial "site
> supply". Not so daft, as I'll be working of a site supply initially
> until I get all the old cabling stripped and walls chased. But it gauls
> me as I've already paid the BCO the BNA fee.
> 
> 3) Be naughty and pull the DNO's fuse. That however gives EDF an excuse
> to get involved and I still have the issues in (1) regarding the henley
> block.
> 
> Any advice before I open the can of worms by phoning their networks
> division on Monday?
> 
> Many thanks,
> 

Building control may wish to see the installation form time to time but 
in all likelihood, they'll simply ask to see the EIC. They may ask if 
your part P registered. Make it clear that you know more than the BCO 
about domestic electric installation, and wave the test results under 
their nose. The important thing it to emit all the signs of competence, 
becaus that is the reality. 

AKAIK there is nowhere on the EIC which requires that a "guild" 
registration number is written down. [1]

So get yourself the right test gear and complete the EIC and sign it, 
obviously you'll be designing, installing, inspecting and testing it 
yourself. 

If the incomer and meter are in a suitable place then you won't even need 
to bother EDF. The only way EDF will need to be involved is if you are 
wanting the incomer, cut-out and/or meter relocated.

[1] This is different to say a Gas Safety Certificate or Boiler 
Commissioning Page. 
-- 
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk 
Gas fitting FAQ  http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

Hi Ed,

Ed Sirett coughed up some electrons that declared:


> 
> Building control may wish to see the installation form time to time but
> in all likelihood, they'll simply ask to see the EIC. They may ask if
> your part P registered.  Make it clear that you know more than the BCO 
> about domestic electric installation, and wave the test results under
> their nose. The important thing it to emit all the signs of competence,
> becaus that is the reality.

At the moment, there's a lot of flux in the plans. As the plans for the
electrical systems stabilise, I'll be doing a formal design which I plan to
hand over to the BCO. Essentially a page for each final circuit,
demonstrating that grouping, derating factors and calculated loop
impedances are tolerable for the chosen cable CSA. Another for
earthing/bonding arrangements and one for submain and protection, if
relevant (I may be happier getting an engineer's opinion on that, akin to a
beam calc for structural work.)

> 
> AKAIK there is nowhere on the EIC which requires that a "guild"
> registration number is written down. [1]

Concur, I've had a good look.

> So get yourself the right test gear and complete the EIC and sign it,
> obviously you'll be designing, installing, inspecting and testing it
> yourself.
> If the incomer and meter are in a suitable place then you won't even need
> to bother EDF. The only way EDF will need to be involved is if you are
> wanting the incomer, cut-out and/or meter relocated.

This is the floating in the ether. Right now, I have a weird arrangement.
ASCII art time:

               Roof
============ Soffit line ======================
                          | |  | |
           Side Wall      | |  | | < 2" plastic pipes
                          | |  | | < carrying final circuits
                          | |  | | < into roof space
  --------------       --------------
  |  EDF box   |       |            |
  |            |       |  Main CU   |
  |  Meter     |-------|            |
  |            |  Tails|  Henley    |
  |            |-------|            |
  |  Supply    |       | Random     |
  |   Head     |       | Extra Fuses|
  --------------       --------------
        |
        |Main
        |Incomer
        |
        |
        |
        |
        |
   
      Ground


I'm not sure why the CU is outside, not something I agree with irrespective
of regs.

So, Options:

1) is new CU inside house behind EDF box. Not the best siting
option and EDF needed to move and extend tails in order to lose
external CU box (it's a genuine 2nd EDF box bought off them by the previous
occupier). Otherwise I could run new tails from the current henley, not so
neat because I've got an entire meter box for one connector block.

2) Move supply round by front door. EDF are quite good at moleing without
vast amounts of destruction, but it's gonna cost me, a lot I would think.
At the technical level this is the best solution. But it's also the option
that probably gives them most scope to whine.

3) Put the CU where I want and run a BS88-2 fused submain with switch-fuse
and SWA terminator box in 2nd cabinet. Looking like 25mm2 SWA will be
required, absolute minimum and that's hellishly heavy stuff, especially in
3 core which I may well need to keep loop impedances low. I've done the
calcs for the submain vis-a-vis BS88-2 in isolation, but I really need to
do some worst case final circuit calcs to make sure volt drop and tripping
times at each level remain in spec. Can keep EDF fully out of the loop,
legitimately which is a bonus. Technically, is either a prudent alternative
to moving the supply head or a very involved way to avoid technicalities.

Think I shall be free and frank with the on Monday WRT to it being a
building control job. They might be OK about it, we'll see.

It's embarrasing. SWMBO formed a kitchen and 2 bathroom plans in a 10th of
the time it's taking me to decide where to put the CU. :~|

> [1] This is different to say a Gas Safety Certificate or Boiler
> Commissioning Page.

Out of interest, what happens if one has a boiler with no Commissioning
page. Is this a "gas thing" or a "Part L" thing or both?

Cheers

Tim

dorothybradbury@dorothybradbury.co.uk coughed up some electrons that
declared:

> On Jul 20, 2:53 am, Tim S  wrote:
>> http://www.tlc-direct.co.uk/Products/TM9083P.html
> 
> That is 383+VAT.
> I would also look at the Megger MFT 1552 for about 60 more,
> it is well regarded and might have a better resale value later.

That looks like a nice instrument, 1000V test which I heard is useful on
pyro. I saw some issues with tripping 6A MCBs, although it's apparantly
fixed via an upgrade: something to note if buying second hand.

> 
>> Do you recall if the supplied test leads are fused?
> 
> Fused test leads are worth it, and typically quite expensive.
> 
> Alternatively, you could hire a meter when ready and spend
> the saving on going all RCBOs or a triple RCD wide CU.

I think this is a test instrument I'd like to own. The wiring will not be
completed in one sitting - various extra (external) circuits will be added
later.

I am going to use RCBOs throughout. Considering SPSN (DP) modules and a
suitable board with L/N busbar - neatens it up a lot not having all the
neutral tails and DP isolation is nice, though not required. MEM do such a
board, but only to 8-ways - at this rate I'll need two stacked - upto
around 10-11 final circuits.

If anyone has any recommendations for a CU, I'd like to hear them.

My primary considerations are:

1) Lots of space, no cramped wiring.

2) RCBOs that have visual indication of earth trip vs overload trip.

3) (Nice but not essential) DP board

4) >=14 final circuits, preferably off a single incoming isolator.

Cheers

Tim

Tim S wrote:

> 1 Are there any issues with a main bond around 15 meters long to reach the
> gas and water incoming services from the proposed MET position?

No, provided that the route is sensible wrt mechanical damage of the 
conductor, etc.

> I assume it is sized to achieve a certain impedance? (Haven't got
> that far through the wiring regs yet).

No, sizing is all on CSA: not less then half the size required for the 
earthing conductor for TN-S, or according to Table 54.8 for PME.  The 
latter sizes the bonding as a function of the supply neutral size - 10 
mm^2 for a neutral not exceeding 35 mm^2 covers almost all domestic 
supplies.

There is a /recommendation/in GN3 that the measured resistance when 
tested for continuity should be < 0.05 ohm.  That allows you 27 m of 10 
mm^2 copper at 1.83 milliohm/m without any controversy.

> 
> 2 Are there any restrictions on the flammability of a board the CU +
> accessories are fixed to. I was thinking of lining the back of such a
> cupboard with ply? I know there is an issue with old open backed equipment.

Not for modern equipment which is all totally enclosed.
> 
> BTW, did you bother with a 100mA time-delayed RCCB for your temporary TT
> system (bit pointless with a single final circuit I know).

That's n/a - there were no fixed equipment circuits, only sockets for 
which a 30 mA fast RCD is required.

-- 
Andy

Andy Wade coughed up some electrons that declared:

> Tim S wrote:
> 
>> 1 Are there any issues with a main bond around 15 meters long to reach
>> the gas and water incoming services from the proposed MET position?
> 
> No, provided that the route is sensible wrt mechanical damage of the
> conductor, etc.
> 
>> I assume it is sized to achieve a certain impedance? (Haven't got
>> that far through the wiring regs yet).
> 
> No, sizing is all on CSA: not less then half the size required for the
> earthing conductor for TN-S, or according to Table 54.8 for PME.  The
> latter sizes the bonding as a function of the supply neutral size - 10
> mm^2 for a neutral not exceeding 35 mm^2 covers almost all domestic
> supplies.
> 
> There is a /recommendation/in GN3 that the measured resistance when
> tested for continuity should be < 0.05 ohm.  That allows you 27 m of 10
> mm^2 copper at 1.83 milliohm/m without any controversy.
> 
>> 
>> 2 Are there any restrictions on the flammability of a board the CU +
>> accessories are fixed to. I was thinking of lining the back of such a
>> cupboard with ply? I know there is an issue with old open backed
>> equipment.
> 
> Not for modern equipment which is all totally enclosed.
>> 
>> BTW, did you bother with a 100mA time-delayed RCCB for your temporary TT
>> system (bit pointless with a single final circuit I know).
> 
> That's n/a - there were no fixed equipment circuits, only sockets for
> which a 30 mA fast RCD is required.
> 

Cheers Andy :)

Tim S wrote:

> 3) Put the CU where I want and run a BS88-2 fused submain with switch-fuse
> and SWA terminator box in 2nd cabinet. Looking like 25mm2 SWA will be
> required, absolute minimum and that's hellishly heavy stuff, especially in
> 3 core which I may well need to keep loop impedances low.

Have you considered using 25 mm^2 split-concentric service cable (BS 
7870) for this?  It's smaller and more flexible than SWA, has a 16 mm^2 
copper earth and doesn't need big brass glands.  It's commonly used for 
service distribution circuits in blocks of flats, from a common intake 
or meter room to the individual flats.

-- 
Andy

Andy Wade coughed up some electrons that declared:

> Tim S wrote:
> 
>> 3) Put the CU where I want and run a BS88-2 fused submain with
>> switch-fuse and SWA terminator box in 2nd cabinet. Looking like 25mm2 SWA
>> will be required, absolute minimum and that's hellishly heavy stuff,
>> especially in 3 core which I may well need to keep loop impedances low.
> 
> Have you considered using 25 mm^2 split-concentric service cable (BS
> 7870) for this?  It's smaller and more flexible than SWA, has a 16 mm^2
> copper earth and doesn't need big brass glands.  It's commonly used for
> service distribution circuits in blocks of flats, from a common intake
> or meter room to the individual flats.
> 

No I hadn't - default reaction because I've made off SWA before and it's
what I've seen the most of in it's general class.

But... Just had a look, split concentric does look better, 3mm smaller on
the diameter and a quid/m less. Is the method of making off just to strip
the neutrals and twist into a single form, ditto CPC minus the stripping?
Or is there a special method? Google drawing a blank...

Cheers

Tim

Perhaps of academic (rather than practical) note unless your cable
route & installation method is to plaster in split concentric :-)

Split Concentric does not comply with 526-06-06 in 17th.
No RCD required if the cable is run on the surface, in steel trunking/
conduit, or at >50mm depth etc (note BReg AD "A" imposes limits on
wall chasing depth).
However RCD would be required if you just buried the cable under
plaster. RCD protection of a sub-main is no good because you would
lose any final circuit downstream RCD discrimination.

SWA does comply with 526-06-06 in 17th.
No RCD required if the cable is just buried under plaster, however the
size & min bend radius (6*Dia) probably prevents this anyway.



A comment re EFLI testing.
Buy a copy of GN3 re testing.
The 15ma no-trip EFLI measurement sounds good, but I am not totally
convinced by their efficacy.
No trip EFLI measurement is indirect via a complex algorithm & tiny
test current. If any noise is present during the test the results can
suffer poor reproduceability & accuracy, sensitivity analysis of some
algorithms is poor. Noise can occur from fluorescent lights (turn off
neighbouring CPD), appliances accidentally left plugged in, proximity
to the Tx, harmonics etc, even battery level.
Eg, Low current EFLI test may produce Zs results varying from 0.9ohm
to 1.4ohm which makes validating a circuit design meets Zs limits for
a 40A+ Type-B CPD rather ambiguous.
Eg, Low current EFLI test results lose accuracy as Zs gets very low
(TN-C-S) - an issue if validating say sub-main fuse protection. Meter
accuracy can be a flat +/- 10% or a tighter %age with +/- 4-digit
variation to consider. I notice calibration certificates are at high
Zs levels, such as 0.7-1.0ohms (TN-S supply Ze).

With a low test current the algorithm is highly sensitive, noise may
not be rejected but actually magnified. With high current EFLI tests
this does not occur, noise that affects a 15ma test is insignificant
in a 25A test - but the high current test will trip an RCD.

EFLI testers are live testers.
That exposes you to live testing risks (25A test at light fittings
will spark at probes). That exposes you to instrument selection (three
wire testers can not be N+E joined to test no-neutral light switches
without tripping the RCD). Fused test leads are ideally required,
which adds to the cost.

EFLI can be determined dead.
Regulations permit calculation of Zs - measure R1+R2 via 200ma
continuity meter, obtain Ze from supply-type & DNO enquiry (TN-S
0.80ohm, TN-C-S 0.35ohm) or simply measure Ze. PFC obtained from DNO
enquiry. Make up your own wander lead or socket adapter (make buy one
with 4mm bridge lead as necessary). Some find hook test leads are
quick.

Some EFLI meters will measure R1+R2 for you (recent Megger 2-wire
testers, LTW325 IIRC) which can save time. Multiple boxes incur
multiple calibration charges, single boxes incur less but are a single
point of failure.

Just a few comments.
--
DB.

Hi, thanks for the detailed reply :)

dorothybradbury@dorothybradbury.co.uk coughed up some electrons that
declared:

> Perhaps of academic (rather than practical) note unless your cable
> route & installation method is to plaster in split concentric :-)
> 
> Split Concentric does not comply with 526-06-06 in 17th.
> No RCD required if the cable is run on the surface, in steel trunking/
> conduit, or at >50mm depth etc (note BReg AD "A" imposes limits on
> wall chasing depth).
> However RCD would be required if you just buried the cable under
> plaster. RCD protection of a sub-main is no good because you would
> lose any final circuit downstream RCD discrimination.
> 
> SWA does comply with 526-06-06 in 17th.
> No RCD required if the cable is just buried under plaster, however the
> size & min bend radius (6*Dia) probably prevents this anyway.
> 

Thanks for clarifying that. I hadn't got that far, but I guessed
that having a neutral (which should be regarded as "live" as much as
line/phase) wrapped around the line conductor would not be
considered "protection". I have three routes, underground, clipped direct
to external wall, via loft space on cable tray.

> 
> A comment re EFLI testing.
> Buy a copy of GN3 re testing.

I'll look into that.

> The 15ma no-trip EFLI measurement sounds good, but I am not totally
> convinced by their efficacy.
> No trip EFLI measurement is indirect via a complex algorithm & tiny
> test current. If any noise is present during the test the results can
> suffer poor reproduceability & accuracy, sensitivity analysis of some
> algorithms is poor. Noise can occur from fluorescent lights (turn off
> neighbouring CPD), appliances accidentally left plugged in, proximity
> to the Tx, harmonics etc, even battery level.
> Eg, Low current EFLI test may produce Zs results varying from 0.9ohm
> to 1.4ohm which makes validating a circuit design meets Zs limits for
> a 40A+ Type-B CPD rather ambiguous.
> Eg, Low current EFLI test results lose accuracy as Zs gets very low
> (TN-C-S) - an issue if validating say sub-main fuse protection. Meter
> accuracy can be a flat +/- 10% or a tighter %age with +/- 4-digit
> variation to consider. I notice calibration certificates are at high
> Zs levels, such as 0.7-1.0ohms (TN-S supply Ze).
>
> With a low test current the algorithm is highly sensitive, noise may
> not be rejected but actually magnified. With high current EFLI tests
> this does not occur, noise that affects a 15ma test is insignificant
> in a 25A test - but the high current test will trip an RCD.
> 
> EFLI testers are live testers.
> That exposes you to live testing risks (25A test at light fittings
> will spark at probes). That exposes you to instrument selection (three
> wire testers can not be N+E joined to test no-neutral light switches
> without tripping the RCD). Fused test leads are ideally required,
> which adds to the cost.
> 
> EFLI can be determined dead.
> Regulations permit calculation of Zs - measure R1+R2 via 200ma
> continuity meter, obtain Ze from supply-type & DNO enquiry (TN-S
> 0.80ohm, TN-C-S 0.35ohm) or simply measure Ze. PFC obtained from DNO
> enquiry. Make up your own wander lead or socket adapter (make buy one
> with 4mm bridge lead as necessary). Some find hook test leads are
> quick.
> 
> Some EFLI meters will measure R1+R2 for you (recent Megger 2-wire
> testers, LTW325 IIRC) which can save time. Multiple boxes incur
> multiple calibration charges, single boxes incur less but are a single
> point of failure.
> 
> Just a few comments.

That's very kind - thanks. I have a science background, but it'll take a
couple more read throughs to fully digest. I think I need to download some
manuals for a couple of potential purchases testers and look into this in
more detail.

Cheers

Tim

On 18 Jul, 20:43, Tim S  wrote:

> I don't have any problem providing an EIC as an unqualified person (in fact
> it is becoming a point of pride to make sure I do everything correctly to
> the 17th), but if EDF won't accept it and no-one else can do it, then I'm
> stuffed.

I'm likely to be in the same position soon. Is it worth upgrading my
on-site guide from 16th to 17th?

Andy Dingley coughed up some electrons that declared:

> On 18 Jul, 20:43, Tim S  wrote:
> 
>> I don't have any problem providing an EIC as an unqualified person (in
>> fact it is becoming a point of pride to make sure I do everything
>> correctly to the 17th), but if EDF won't accept it and no-one else can do
>> it, then I'm stuffed.
> 
> I'm likely to be in the same position soon. Is it worth upgrading my
> on-site guide from 16th to 17th?

Unfortunately it's not out yet. Mid August is the estimate I last came
across and Amazon are saying pre-order for 1/09/2008.

Cheers

Tim

Tim S coughed up some electrons that declared:


> We'll see what they say when I ring EDF's networks division on Monday.
> 

Found a random number on the web and managed to get straight through to the
department for moving supplies.

Answers:

700 squid (order of magnitude guesstimate on their part) to move an
underground cable and relocate supply head from side to front of house.
Confirmed that an EIC would be needed, but we didn't go into the why's and
wherefore's of registered/non registered person completing said EIC. Didn't
go into moving tails or isolators - I'll assume that'll be around 100 quid.

I knew I was onto a good thing having found an actual technical department, 
so decided not to push good fortune too hard in one sitting. So I got the
Ze and PFC data out of them, PFC 16kA, Ze 0.35 Ohms. Good, that's one bit
of research done. 

Went on to asking about earthing arrangements. Given another number and name
of person in what turned out to be the uber-technical department. 

Really helpful chap there, carefully looked up the records and confirmed
that I had TN-S. Result...

Also found a firm of Consulting Electrical Engineers not very far from here.
Asked if they'd be up for doing a small job: producing a written
calculation on the cable and protection required on a 100A submain, in the
context of the service and final circuit protection. They said they didn't
mind the odd small job, about 2 hours at 58+VAT/hour. They told me all the
information they'd need, which I knew anyway.

Cable sizing isn't particularly hard, but I do want to be confident that
there will be adequate discrimination between the submain fuse and all the
downstream RCBOs as well as ensuring that the protection at each level is
able to operated in the prescribed times. 

Reckon I could have a go at the calcs (done the fault disconnect time check
already) and I will try the whole thing as an academic excercise, but it's
a bit like "having a go" with SuperBeam for the RSJ that's holding my house
up. Probably get fairy close with a following wind, but I'm not betting my
life on it. Besides, having a formal document will be good for the file and
might impress the BCO, we'll see.

Time for further reflection to see if there's any way I can get the CU near
the meter without undue compromise. It's a weird house, nothing is obvious,
takes a time to come to a conclusion about anything.

We'll see...

Cheers

Tim