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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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 04 January 2013 12:48 AM
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AJJewsbury

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Why not? If it walks like a duck, and quacks like a duck, what's objection to to ticking a box labelled duck?
- Andy.
 04 January 2013 01:07 AM
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spinlondon

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Originally posted by: leckie
So we tick the double insulation box for basic and fault protection in just about every case because we fit 6181Y tails?

I dont think Sensei Geoff would approve

Are you suggesting we don't tick the box for ADS?
I don't really think that T&E cables are double insulated.
 04 January 2013 07:29 AM
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leckie

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So twin and earth isn't double insulated, I agree.
So you think meter tails are double insulated and it's not just a slang term used, as Bod pointed out earlier, for things likes meggar (insulation tester), with no box within a box label? Not sure.

If you think so, perhaps flex is double insulated? No bare cpc?

Do we now think that 6181Y give both fault and shock protection because we think they are double insulated?

Why do dno's give a max length of say 2.5m for tails before they require you to fit a switch fuse or similar device? Is it because that's the max distance they will allow there cut out fuse to protect the meter tails?

I said earlier I was get confused. Now I'm merely baffled

Edited: 04 January 2013 at 08:32 AM by leckie
 04 January 2013 12:30 PM
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spinlondon

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Do you really think that both manufacturers and wholesalers would use a slang term to describe a cable if it wasn't as described?
That they would use a term that would suggest the cables have properties that they don't in fact have?
Would they really put themselves into a position, leaving themselves ripe for litigation?
As someone has already pointed out, there is no requirement to use the box within a box symbol with cables.

The DNO's as far as I'm aware allow a max length of 3m.
Perhaps that's half a meter from the cut out to the meter then the 2.5m that you quote from the meter to the switch fuse.
The distance has nothing to do with their fuse protecting your tails, the DNO's fuse is there to protect their equipment, as per the statutory requirement.
The 3m distance being taken from Regulations 433.2.2 and 434.2.1, for positioning protective devces where there is a reduction in the CCC of a conductor.
 04 January 2013 05:15 PM
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leckie

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So we are ticking the double insulated box in an installation even if there are no class 11 fittings, no selv lighting with remote Tx's, etc, just because there are meter tails fitted?

And this is because the tails are protected against fault and shock because they are double insulated?

Isn't the shock protection provided by the basic insulation albeit insulated and sheathed cable, and fault by the cpc from the system wether it be TNS, TT, etc?
 04 January 2013 06:05 PM
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daveparry1

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So we are ticking the double insulated box in an installation even if there are no class 11 fittings
---------------------
I don't Leckie, I think the box means double insulated accessories not wiring. I know I said a few days ago that insulated and sheathed tails are double insulated but that's just my understanding of the English language, ie double meaning two!

Dave.
 04 January 2013 06:24 PM
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spinlondon

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Leckie, you must be aware that with the majority of domestic TT installations, fault protection is provide by an RCD.
You've posted that you would not use plastic bushes, but instead a plastic enclosure.
Why would you do such if you are unaware of the reason for doing so?
SELV lighting may or may not be double insulated.
The whole point of SELV, is that the voltage and current is so low, that insulation is not really required, hence the bare wire systems.
(Although in my experience of such systems, the wire has not in fact been bare, but insulated with a clear insulation.)
Obviously some other method of fault protection has to be provided for the parts of the installation that are not protected by the RCD.
If it's not double insulation, then what is it?

Edited: 05 January 2013 at 12:22 AM by spinlondon
 04 January 2013 09:44 PM
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leckie

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I agree dave.
Spin, have a read of what I have said. I may have linked a few different subjects and may have confused you
 04 January 2013 10:07 PM
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Zs

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I have not run away and have been watching this thread but taking a back seat to see your real views. I'm liking what OMS would describe as your 'iteration' very much and enjoy the honesty of such. We don't often see a thread on here with changes of mind and open suggestion.

Talking of the honesty, I still don't agree with all of it but am determined not to be bigoted. I still do not think the boxes on these forms in front of me should be ticked. Completely agree with the 'what came in a box?' and doorbell discussion bewtween AJ and GB and that is about the camp I am still in. In truth, I've not moved much from my original view but I've a great deal to look up over the weekend. I am going to be there on 14th Jan. The client of course will be clueless as to all this but trust me, I'll be referring to your posts every step of the way.

I guess we have uncovered a big flaw in the schedule. But over the weekend I will read this thread through thoroughly with big green at my side.

Roger, the forms I have here are exactly the ones which Rutts made in his own time and posted for use on this very forum. They have circulated into industry use very quickly haven't they? As such they are practically identical to the ones in the back of BS7671. In effect, they are the model forms.

Back after I have read everything and digested properly. If someone takes the time to write every word then every word deserves to be read.

Zs
 05 January 2013 02:48 AM
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spinlondon

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As far as I'm aware, this is a schedule of inspections.
Regulation 611.3 gives a list of what sould at the least be inspected.
This list is very similar to the schedule of inspection, and includes SELV, PELV, Double insulation and Reinforced insulation.
The Regulation also indicates that it should be checked that the requirements for special locations in Chapter 7 are met.

Many domestic installations utilise SELV for extractor fans in locations containing a bath or shower.
It is a requirement that where SELV equipment is installed in such locations, that the safety source be installed outside of any zones.

Insulated and sheathed tails aside, the majority of domestic installations utilise double insulation as a protective measure for pendant light fittings.

Many domestic installations utilise electrical separation as a protective measure, admitedly usually only in the form of a shaver socket.
However again there are requirements on where such equipment can be positioned.

Considering that it is a requiremnt for these protective measures to be inspected both on initial verification and during a periodic inspection, and that where used in special locations that the requiremnts for such locations have been met.
I find it rather odd, that anyone would suggest that these boxes should not be ticked, to indicate that an inspection has taken place.
 05 January 2013 08:17 AM
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leckie

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Originally posted by: spinlondon[/

Insulated and sheathed tails aside, the majority of domestic installations utilise double insulation as a protective measure for pendant lights.


So twin flex is classed as double insulated is it? The lampholder is I believe. I've never heard of flex being described as double insulated.
 05 January 2013 11:21 AM
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leckie

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I will try a summary.
433.3 Omission of devices for protection against overload
433.3.1 (iii)
"At the origin of an installation where the distributor provides an overload device and agrees that it affords protection to the part of the installation between the origin and the the main distribution point of the installation where further overload protection is provided."

434.3 omission of devices for protection against fault current
434.3(iv)
"At the origin of an installation where the distributor installs one or more devices providing protection against fault current and agrees that such a device affords protection to the part of the installation where further protection against fault currents provided."

So in fact the cut out fuse does provide protection against overload and fault current to the meter tails providing the distributor agrees. They usually agree providing certain criteria are met, e.g. A minimum cable csa and a maximum length. This length is not always 3m. As Alan Capon mentioned earlier, his employer allows a maximum of 2.5m, it depends of the distributor.

433.2.2 and 434.2.1 is not where the distributor get the 3m max rule from, they do not work to bs7671, they have supply regs. If they did why would different distributors have different lengths?

So in tns, tncs, the protection is from the cut out fuse and we would not tick the double insulated box just because we have installed insulated and sheathed meter tails.

Are 6491x cable installed in PVC conduit consider double insulated, and if so would we tick that box each time we installed that method? No.

If we go to aTT system it gets a bit more opinion based. The tails then have to be installed in double insulated enclosures, or more normally, using insulated and sheathed cables installed in such a manner as there to be little risk of shock or fault. Hence insulated enclosures for the incoming rcd and insulated and sheathed cable, or single insulated cable in an insulated enclosure giving an equivalent protection of double insulation. So to verify this is the case, some may consider it appropriate to tick the box in this case. But I wouldn't.

Some may consider it appropriate to tick the box because they have installed a bit of twin flex to a class 11 lampholder; some may consider that, as I do, very silly indeed.

Edited: 05 January 2013 at 02:05 PM by leckie
 05 January 2013 12:05 PM
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rocknroll

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Talking of the honesty, I still don't agree with all of it but am determined not to be bigoted. I still do not think the boxes on these forms in front of me should be ticked.


You are so right and obviously have given this lot of thought and applied the necessary logic to the problem, as I said in my opinion these boxes relate to the parameters of the installation as per BS7671 to the electrical outlet so is it;

A unmonitored basic insulation and earth installation that requires the presence of an ELI to the electrical outlet.
TN-C-S
TN-S
TT

Or is it a insulation monitored unearthed installation that does not require the presence of an ELI to the electrical outlet.

Double Insulated
Reinforced Insulation
IT

As I pointed out you can put what you like in the boxes as no-one other than yourselves pay any attention to anything beyond the front page, at my previous time at DBC I watched peoples reaction to these grossly OTT forms, they only looked at the first page to confirm the clients details and maybe checked for a signature then checked a tick box on the BRCC issuance form. housing authority form, licencing authority form etc; then if the cert was a copy it was shredded and if an original returned to the client.

For a simple domestic installation all you need is two pages, one outlining the clients name, address and basic details of the installation and the other page outlining the circuit details and any test results and thats all that BS EN 60364 recommend, but we are really good at generating miles of useless unfriendly paperwork that people tend to ignore.

LOL Carry on!!!

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!"
-------------------------
 05 January 2013 02:43 PM
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spinlondon

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Leckie if the distributors agree that their fuse may be used to provide protection for your, or part of your installation, fine.
If you think that the distributor will take responsibility for any part of your installation, dream on.
How exactly does you complying with BS7671 mean that the distributor is working to BS7671?
The distributor has a statutory obligation to refuse a connection to an installation, unless that installation complies with either BS7671 or ESQR.
Yes there is a bit of confusion over the length of tails.
BS7671 say max 3m from the point of reduction in the CCC of a conductor.
However your installation begins at the consumer connection terminals, I.e at the meter.
BS7671 does not apply for the distributors' equipment.
So where does the 3m start?
At some point on equipment that is not part of your installation and outside of the scope of BS7671, or from the point where your installation begins and BS7671 applies?
 05 January 2013 03:00 PM
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leckie

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Originally posted by: spinlondon

Leckie if the distributors agree that their fuse may be used to provide protection for your, or part of your installation, fine.

If you think that the distributor will take responsibility for any part of your installation, dream on.
[Not what I said, the regs I quoted says we can omit overload and fault protection to tails if the DNO agree, that what the regs say not me/B]

How exactly does you complying with BS7671 mean that the distributor is working to BS7671?

Again not what I said, I only said that the DNO do not work to BS7671

The distributor has a statutory obligation to refuse a connection to an installation, unless that installation complies with either BS7671 or ESQR.

Yes there is a bit of confusion over the length of tails.

BS7671 say max 3m from the point of reduction in the CCC of a conductor.
[]B]I know but the DNO are not working to BS7671, just ESQR[/B
]

However your installation begins at the consumer connection terminals, I.e at the meter.
[B]Correct[/B]

BS7671 does not apply for the distributors' equipment.

So where does the 3m start?

At some point on equipment that is not part of your installation and outside of the scope of BS7671, or from the point where your installation begins and BS7671 applies?
I assume we concur on this?


I dont understand what you have a problem with really Spin, Ive quoted the regs as I see being applicable and i dont think they are incorrect. And I think they means, dont tick boxes for installation of tails, but you a free to do so if you wish.

I think RnR's post are the most sensible on this subject.

Edited: 05 January 2013 at 03:06 PM by leckie
 05 January 2013 03:08 PM
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leckie

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Unfortunately Im not used to using the quotes, bold, italics, etc so my last post is a mess!
 05 January 2013 04:33 PM
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spinlondon

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My problem, is that no one has yet put forward a valid reason or explanation as to why these boxes should not be ticked.
The Regulations require us to inspect and test the items refered to in the checklist.
As far as I can see, the only reasons being pu forward are that the boxes refer to the installation as a whole, or that another method of protection takes precedence.

Unfortunately there is nothing in BS7671 to support these veiws, in fact Regulation 611.3 to my mind indicates the oposite.

You in particular are stating that despite insulated and sheathed tails meeting the definition of double insulated or reinforced insulation and manufacturers' describing then as being double insulated, appear to be stating that they are not in fact double insulated.
However you do not seem able to or willing to explain why they are not double insulated.
At one point you proposed that fault protection is provided "by the CPC from the system whether it be TN-S, TT, etc."
CPCs do not provide fault or in fact any form of protection.
They earth conductive-parts, and provide a path for earth fault current.
Which enables a protective device (if one is present) to operate.

You then went on with your summary.
Your first point would only apply to a TN installation, not to a TT installation, and then only if the DNO agreed, something that in 99.999999% of cases just isn't going to happen.
However you appear to believe the DNOs' routinley do allow their fuse to protect your equipment citing the max length as proof.
The max length you cite, however is not proof of such, in fact it proves the opposite, as it is the length taken from BS7671 Regulations which allow protective devices to be placed downstream from a point in the reduction of a conductor's CCC.

You disagree that the max length is taken from BS7671, as the DNOs' do not work to BS7671.
It would appear that you have either forgotten or are unaware that the DNOs have a statutory obligation to ensure that any installation they allow a connection to, complies with either BS7671 or ESQR.

You then go on to say that as the DNOs' fuse provides protection to the tails we do not need to tick the box for double insulation with TN systems.
If the double insulated tails are not providing the protection, why then are they being installed?
Are they cheaper?
Or do they provide another method of protection i.e. double insulatin?
If they are providing another method of protection, why would we not inspect them to ensure they do provide that other method of protection?
Why would we not tick the box in the check list to show that we have made the inspection?

You mention 6491x cable installed in PVC conduit., and ask whether it is considered as being double insulated and if so do we tick the box, then answer no.
Is that no we do not consider it to be double insulated, or no we do consider it to be double insulated, but don't inspect it, or if we do inspect, we don't tick the box to indicate we have inspected it?

You thengo on to mention TT installations, and say something about tails being in double insulated enclosures?
Not aware of any such requirement, perhaps you could elucidate?
The tails would have to be terminated in a double insulated enclosure, if that is the method of protection used to protect the tails.

You then go on to state that you would not tick the box indicating that you have inspected the tails and the enclosures to ensure that the method of installation does provide the method of protection.
Why would you not tick the box?
Is it because you would not make the inspection, or that you would make the inspection, but don't consider that you need to indicate that you have done so?

Then you indicate that ticking the box is silly.
If that's the case, why tick any box at all?
Is one box more silly than another?
 05 January 2013 04:45 PM
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spinlondon

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That was quite a long post dealling with various points and issues.

To my mind it all boils down to this:
If you provide a method of protection, whether it be to a single item of equipment, to part of an installation or to the whole installation, should you inspect to ensure that the requirements of BS7671 have been met?
Should you inspect to ensure that the requirements of BS7671 have been met for each method of protection, when two or more methods are used.
Should you then indicate that such an inspection has been made by ticking the appropriate box on the check list?

My opinion obviously is yes, yes and yes.
I would like those who are of the opinion 'no', to explain why?
 05 January 2013 06:55 PM
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perspicacious

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However, "meter tails" (sic) or 6181Y are covered by BS 6004 and this makes reference to PVC insulated and PVC sheathed cable
From my copy of BS 6004:2000 Amended to 26 April 2005 (so it is not the latest, that being BS 6004:2012 published on 30/9/2012).....

"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?

"Do you really think that both manufacturers and wholesalers would use a slang term to describe a cable if it wasn't as described?
That they would use a term that would suggest the cables have properties that they don't in fact have?
Would they really put themselves into a position, leaving themselves ripe for litigation?"


It looks as if we'll have to wait for the manufacturers to return to work on Monday to respond to Spin's request for the source of their alleged quote...........

Regards

BOD
 05 January 2013 08:30 PM
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davezawadi

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Double and reinforced insulation have very specific meanings. Cables of "any" type are not double insulated or of reinforced insulation. But the only person who understands this seems to be R&R. What has happened to the industry? A real "double insulated" sheathed cable would have three layers of material, two of which individually would have the ability to withstand an AC flash test for one minute. So insulated and sheathed cables simply do not meet the requirement. The outer covering of a wire or cable (unless singles intended to be installed inside mechanical protection) is simply a mechanical protection, its insulating value is entirely irrelevant (and not specified by the relevant standards).

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David
CEng etc, don't ask, its a result not a question!
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IET » Wiring and the regulations » Double and reinforced insulation

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