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Topic Title: Double and reinforced insulation
Topic Summary: Definition
Created On: 31 December 2012 12:11 PM
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 31 December 2012 06:11 PM
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Zs

Posts: 3037
Joined: 20 July 2006

Roger, thank you for your erudite post. I agree with all of it.

In fact, the certificates I am looking at have already been issued to the person ordering the work so getting boxes 'unticked' is not going to happen. If anyone is to untick then it shall be I, on a separate form.

This installation is one of those that has shown problems since being handed over. I do a great deal of reporting on such installations and they usually take the form of a things to do list with reasons why the installation is not performing, regs etc. then months later an Electrical Installation Condition report after it is all sorted. I consult on installations that don't work as they were ordered. I was sparing you the politics for the purposes of checking my own knowledge on why those boxes have been ticked. Looking internally before speaking out, especially on an opinion, albeit that my opinion is well insured.

It is of course a one page schedule of inspections ( for new installation work only) and not the same form which one day I shall be completing for them as part of an EICR.

But there it is on these forms; double insulation and reinforced insulation are ticked. That is unusual and is why I am involved in a quest to understand before I go in. I guess this thread shows why it has been ticked but I shall only really know when I go back. I very much doubt that significant changes have been made to the fabric of the installation. These are simply replacement DBs. Incidentally, as mentioned, it is SWA and not tails but we digressed.

It does seem, so far, that R&R's smiley faces might be the answer. If we lot disagree then it suggests a greyer-than-grey area.

Nonetheless, I still think tails are not double insulated in the way that tick-box means, even if they have two layers of sheath on them.

Now, Stormy Monday and Before You Accuse Me (how apt for this forum) await. The Blackstar tubes will be warmed up by now.

Happy New Year to you all and thank you.

Zs
 31 December 2012 06:14 PM
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John Peckham

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Geoff

412.2.1 applies to Electrical Equipment not just the wiring system. The Part 2 definition defines electrical equipment.

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John Peckham

http://www.astutetechnicalservices.co.uk/
 31 December 2012 06:22 PM
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GeoffBlackwell

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Yes but does that mean you should be inspecting the equipment as a method of protection or just confirming that it is constructed to the required standard and is installed to manufacturer's instructions, etc.

I did try to pin all this down when I was writing stuff for the NICEIC but I could not get any definitive answers.

Regards

Geoff Blackwell
 31 December 2012 06:31 PM
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perspicacious

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"Does your copy of BS6004 refer to the sheath as a layer of insulation?
Perhaps even as a supplementary layer?"


Supplementary:
Reader has finished searching the document. No matches were found.

Perhaps Spin, asking your "reference sources" where they quote from, would be the way to go?

Regards

BOD
 31 December 2012 06:40 PM
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John Peckham

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Geoff

"I did try to pin all this down when I was writing stuff for the NICEIC but I could not get any definitive answers. " So what chance have us mere mortals got of getting an answer. There are probably no correct answers just opinions on interpretations of particular regulations.

I suppose what really maters is when testing loads of light fittings in building and finding them to be unearthed is deciding if they are Class 2 fittings or crap installation work. Looking for a double square sign of the earth symbol crossed through on the fitting can sometimes be productive but not always. You could say not finding the symbol = it can't be Class 2, but it could be.?

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 31 December 2012 06:41 PM
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daveparry1

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when it is used to supply one item of current using equipment?
----------------------
You're thinking of electrical seperation there aren't you Spin?
 31 December 2012 06:55 PM
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spinlondon

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Originally posted by: daveparry1
when it is used to supply one item of current using equipment?
----------------------
You're thinking of electrical seperation there aren't you Spin?

Is not SELV (Separated Extra Low Voltage) electrical separation?

My point being, is that if these boxes are only to be ticked, only if the method of protection has been applied to the whole installation, how is it possible for an installation to be SELV or PELV?
Would there not need to be some sort of transformer in such an installation?
Would not the supply to that transformer be some voltage other than ELV?
 31 December 2012 07:03 PM
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daveparry1

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Yes I suppose so Spin but I was just thinking of that tick box on the EIC that says "electrical seperation for one item of current using equipment", I only tick that if there's a shaver socket. It couldn't really refer to selv lighting or there could only ever be one lamp per transformer?

Dave.
 31 December 2012 07:17 PM
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perspicacious

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"Would there not need to be some sort of transformer in such an installation?"

Can't a motor-generator be used as a SELV source?

Regards

BOD
 31 December 2012 08:28 PM
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spinlondon

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These tick boxes are on the form for EICs.
An EIC can be used for a complete installation, or an addition or alteration to an installation.
If you were to make an addition, to install for instance a SELV fan, would you tick the box marked SELV, or insert N/A.

Edited: 01 January 2013 at 05:28 AM by spinlondon
 01 January 2013 06:40 AM
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GeoffBlackwell

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Originally posted by: spinlondon

These tick boxes are on the form for EICs.

An EIC can be used for a complete installation, or an addition or alteration to an installation.

If you were to make an addition, to install for instance a SELV fan, would you tick the box marked SELV, or insert N/A.


No the box marked SELV is only to be used when SELV provides both Basic and Fault protection. It does not apply when SELV is only providing Fault protection, as is the case with a 'SELV fan'. Its all in the title above the box and in regulation group 414, in particular the last part of 414.4.5 specifically allows SELV as a sole means of basic protection if its conditions are met. This is the bare wire lighting system, etc.

You would need a SELV box in the schedule section Fault protection:. The only boxes there refer to electrical separation which is not SELV (see regulation group 413) - even given that SELV includes a form of 'electrical separation' within it.

Regards

Geoff Blackwell
 01 January 2013 11:29 AM
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rogersmith7671

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Dear ZS
Having re-read my last post i realize I may have appeared a bit high handed; "to satisfy your own interpretation of what "insulation" means", this was not intended to imply that your knowledge or understanding was at fault.
My intention was simply cautionary, in that; when consultation is invoiced and paid for it is usually well received, this is not necessarily the case when offered for free.
I am sure most would agree, the one part of an installation that requires both basic and fault protection is the part that has no fault protection. This is generally the part from the origin to the main switch, some of which are fused to protect the installation downstream.
In some industrial/commercial installations reinforced insulation may be installed during the construction of the main intake equipment, depending on it's design and construction.
In domestic situations standard meter tails are used along with factory applied insulation to associated bus bars (if necessary) these arrangements are usually considered satisfactory.
So unless the origin of the installation is supplied at either SELV or PELV, one of the other methods may be applicable.

Regards.

PS. The supply fuse at the origin is the property of the supply undertaking and is not intended to protect the downstream installation.
 01 January 2013 12:43 PM
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Zs

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No worries Roger, this is where I come to admit what I don't know. Once we step outside of our front doors we are expected to know it all and it serves well to be able to ask, discuss and to get back to a client with a decent knowledge.

If I am to look at the work of a suspected (by the client) incompetent installer then I sure as hell don't want to be turning up as an incompetent inspector. Your words were valid. Every incompetence declared on here rapidly becomes a competence.

I'm watching this discussion with interest. Not only do we differ on the interpretation of double insulation but we also seem to differ on whether or not the tick box gives a general overview of the installation or whether we must diligently search out a single double insulated fitting in order to tick a box, or be considered negligent if we miss it? In my view a DI hunt for an accessory in an otherwise not double insulated installation is spurious. However, I shall keep watching. I doubt that I will be in a poistion to ask the installer, not least because he seems to have taken to the hills.

So we are in the realms of the detailed covering letter. Another example of how our work requires so much more than sums and regs.


Zs

edited a blunder caused by speed reading one of the replies.

Edited: 01 January 2013 at 12:56 PM by Zs
 01 January 2013 02:19 PM
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rogersmith7671

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Dear ZS
The NIc Eic do provide some advice on this subject in their book; Inspecting and reporting, on page 158 which includes two illustrative diagrams to explain the difference.
How deep you should go with any inspection depends on you and the person ordering the work, simply limiting yourself to a percentage or visual only with no dismantling what ever may not reveal what your client wants to know. The question as to whether a dangerous situation may therefore go undiscovered is moot, as only a detailed and more thorough examination would reveal this.
These sort jolly merry-go-rounds can be "limited" by simple negotiation prior to the inspection.
I do agree that it wold be rather invidious to be testing the work of another only to be making errors oneself, so why not "limit" yourself to; "At risk" and "immediately dangerous situations" and leave the "not to current standards" for a more in-depth analysis which may include some "office-time" at an extra cost.
Quote;
So we are in the realms of the detailed covering letter. Another example of how our work requires so much more than sums and regs.
Ain't that the truth!
Regards.

PS The NIC EIC forms ask double or reinforced insulation? The IET version I have asks double? then reinforced? (in that, only they seem to make the distinction).
 01 January 2013 04:06 PM
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spinlondon

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I would not think that when filling out an EIC, it would be much of a chore to diligently search out all the equipment covered by the EIC.
Yes I think it would be negligent to forget to mention something that you've just fitted.
Remember the Schedule of inspection relates only to the work covered by the EIC, not to the existing installation.
 01 January 2013 05:03 PM
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Zs

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ah, slight glitch with the documents, I'm not NIC registered yet. Only if such a thing ever changes from being an option.

Zs


BTW, how cool is that reflection of the Megger crocs in my Humbuckers?
 01 January 2013 05:24 PM
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rocknroll

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The electricity supply industries are bound by legislation to supply a UK domestic customer with 400/230V 50Hz basic insulation and earth supply, anything other than this is by special arrangement, under the terms of BS7671 the installation derived from this to the electrical outlet must be the same, basic insulation and earth and this is what the whole system of basic and fault protection is designed and installed around hence the need for an earth loop fault impedance, if you use double or reinforced insulation cable an earth must still be present so it does not make the installation either of the above and still is classed as basic insulation and earth so it does not change, a double or reinforced installation does not require the presence of an earth loop impedance.

All I was making was a technical point that BS7671 stops at the electrical outlet and anything connected like a 110v transformer, lighting transformer and any other accessory is covered by seperate standards.

In my opinion the three boxes referred need not be filled in for a standard domestic installation to the electrical outlet because basic and fault protection is covered by basic insulation and earth not SELV, Double or Reinforced insulation.

But as I pointed out fill in what you like. You normally do!!

Disagree all you like its my opinion.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
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 01 January 2013 05:42 PM
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Zs

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Go Rock. I agree with your posts and they make a great deal of sense.
 02 January 2013 08:47 AM
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Parsley

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Zs

From your description of the installation I would not tick the box.

I believe it should only be ticked if the protective measures against electric shock throughout the entire installation are provided by double or reinforced installation only.

Refer to 412.1.3 and section 5 of GN 5 exert below.

"The protective measure of double or reinforced insulation may only be used as the sole means of protection against electric shock for an installation or circuit under effective supervision in normal use. This is to ensure that no changes are made that would impair the effectiveness of the protective measure.
In this case the whole installation or circuit should consist entirely of equipment with double insulation or reinforced insulation.
This protective measure must not therefore be applied to any circuit that includes a socket-outlet, luminaire supporting coupler (LSC), device for connecting a luminaire (DCL) or cable coupler, or where a user may inadvertently or in ignorance replace Class II equipment with Class I (requiring an earth)."

Regards
 02 January 2013 01:42 PM
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AJJewsbury

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The electricity supply industries are bound by legislation to supply a UK domestic customer with 400/230V 50Hz basic insulation and earth supply

But which legislation Rock? I can't find any reference to 400V in the The Electricity Safety, Quality and Continuity Regulations - is there something else that I've overlooked?

In my view - in general these boxes refer to the assembly of the installation and not to the individual parts as these are already covered by product standards.

So what about a door bell circuit? Transformer, lots of cable (typically not sheathed), Probably not IP rated bell push outside in all weathers? All put together on-site. Is the suggestion that the protection from electric shock is by earthing/ADS??

No the box marked SELV is only to be used when SELV provides both Basic and Fault protection. It does not apply when SELV is only providing Fault protection

I could argue that a SELV circuit always does. Just because you also have another means of basic protection as well doesn't detract from that. Indeed for SELV circuits over 25V a.c. or 60V d.c. additional basic protection is a requirement (reg 414.4.5) of the SELV system itself - so not relying on the extra-low/separated nature of the voltage alone. So saying if basic insulation is present, it isn't SELV doesn't seem to add up.

Such a strong feeling that two layers on a tail does not constitute double insulation. It is no different to a single thicker layer, just more colourful.

How about an experiment - give a spare bit of T&E or meter tail a bash with a hammer or brick bat - a few glancing blows until there's obvious damage to the outer sheath. I'd put 5p on the sheath parting from the inner insulation, which remains intact.

I believe it should only be ticked if the protective measures against electric shock throughout the entire installation are provided by double or reinforced installation only.

The title of the section (on the BS 7671 model one at least) is "Methods of protection against electric shock" - methods, plural. Isn't that inviting us to tick all that apply, rather than 'pick one'?

- Andy.
IET » Wiring and the regulations » Double and reinforced insulation

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