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Topic Title: Double Insulation
Topic Summary: Schedule of Inspections
Created On: 21 April 2013 03:40 PM
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 21 April 2013 03:40 PM
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deapea

Posts: 370
Joined: 13 May 2007

There was a thread on this subject recently which became very long with differing views:

http://www.theiet.org/forums/f...MP=Linear&#lastunread

Can someone summarize the outcome of this please?
The simple questions are:
1. where pvc insulated and sheathed cables are used on an installation should we tick the box indicating that double insulation is being used for both basic and fault protection?

2. where plastic surface mounted accessories with no exposed conductive parts are used on an installation should we tick the box indicating that double insulation is being used for both basic and fault protection?

Thanks.
 21 April 2013 04:11 PM
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daveparry1

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1. my view was no because although t/e does have two layers of insulation this doesn't constitute "double insulation" as such. Have you ever seen the square whithin a square on a length of t/e cable?

2. also no because unless the whole installation consisted of double insulated accessories how could you call it a "double insulated" installation?

That's my view anyway, probably plenty of other people will have different ideas though!

Dave.

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 21 April 2013 04:19 PM
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leckie

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I think you should read it all

Don't tick the boxes for either of those examples. N/A in the boxes.

The electricity safety council confirmed this in one of there answers to questions.

Here
http://www.esc.org.uk/industry...faq-search/?no_cache=1
 21 April 2013 04:20 PM
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leckie

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That should get the box tickers started!
 21 April 2013 05:31 PM
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Legh

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IMO, Do not tick Double Insulation since this refers to the main method of protection and not as a supplementary/additional add on. The main method of protection would be ADS.
Legh

-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 21 April 2013 06:38 PM
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Martynduerden

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1. No it's not double insulated its insulated & sheathed.

2. No, it is not a double insulated product.

Some extractor fans are double insulated.. So you might tick it for that.

-------------------------
Regards

Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com
 21 April 2013 10:30 PM
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leckie

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No you wouldn't Martyn. Well you might, but you shouldn't.
 21 April 2013 11:20 PM
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Martynduerden

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Originally posted by: leckie

No you wouldn't Martyn. Well you might, but you shouldn't.


Lol, I'm beginning to think that it's a redundant box

-------------------------
Regards

Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com
 21 April 2013 11:34 PM
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leckie

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Well most of the time it is. I have never done a double insulated installation, only ADS. And I am mature. Err well, old actually. But I have installed meter tails, twin and earth, class2 fittings, etc.

Do not tick. If your not sure ask you Napit assessor, he won't know either

But don't trust me, I've been bonding water pipes with a plastic incomer for 40 years!
 22 April 2013 08:01 AM
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zeeper

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Wasnt the same argument made about selv circuits. Or is that different again.

Like where you have extra low voltage light. tick or not
 22 April 2013 09:03 AM
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leckie

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Don't tick, I think the ESC questions and answers also says don't tick.
 22 April 2013 11:50 AM
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zeeper

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Don't tick, I think the ESC questions and answers also says don't tick.


Sorry leckie you fell straight into my trap.

Page 158 of the iet on site guide. tick.

with reference to page 159
 22 April 2013 12:12 PM
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Parsley

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Originally posted by: zeeper

Don't tick, I think the ESC questions and answers also says don't tick.




Sorry leckie you fell straight into my trap.



Page 158 of the iet on site guide. tick.



with reference to page 159


I think this is the esc guidance leckie is referring to, it is in the industry guidance section places of work new installations.


Q3.15

An installation uses Automatic Disconnection of Supply (ADS) as a protective measure against electric shock. One or more items of separated extra-low voltage (SELV) equipment are installed. On the schedule of inspections, should the "SELV" box for both basic and fault protection as a method of protection against electric shock be ticked?



No. That part of the Schedule of Inspections is intended for use when a part of an installation relies specifically on that method of protection.
 22 April 2013 12:36 PM
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zeeper

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I think this is the esc guidance leckie is referring to, it is in the industry guidance section places of work new installations.


Seems a reasonable idea, However the iet OSG doesnt agree.
 22 April 2013 09:20 PM
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leckie

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Keep ticking then Zeeper. But you shouldn't be
 22 April 2013 10:28 PM
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Legh

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Back to your OP. (412)

I think that 411.1 takes president

414 is likely to be for specific areas or parts of circuits where it is expedient.

Legh

-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 23 April 2013 03:00 PM
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AJJewsbury

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Can someone summarize the outcome of this please?

I will try to be impartial ... (cue memory of Max Boyce & his phrase 'not that I am biased')

The strong tradition is that we always tick the ADS box (or EEBADS of yore) - seemingly because we're British and we always have done so we always will. Class 2 (whether double insulation, reinforced insulation or acceptable equivalent) is seen as foreign and untrustworthy. (OK perhaps that was a bit biased, try again...)

T&E, sheathed trails etc. don't really give protection against electric shock by means of automatic disconnection - as it has no exposed-conductive-part (or concentric c.p.c.) there's no physical mechanism for reliably initiating a L-PE short that would trigger automatic disconnection. But then the regs don't actually demand that cables in an ADS system are protected with an exposed-conductive-part, just that if there is one it needs earthing. So insulated and sheathed cables are allowed to form part of an ADS system. But likewise they can form part of a double insulated system - as 412.2.4 makes clear.

If you provide a supply to an item of equipment, you typically provide L, PE & N. You don't really care what it then does internally - it might be double insulated, it might be SELV, it might be separated or EHT (CRT TV?) - and (mostly) neither does BS 7671 - the internals of the equipment are down to the appliance standard after all. So there is an argument that you can "ignore" the method of shock protection within individual items of equipment. That's not 100% true of course - BS 7671 does occasionally have opinions about the internal protection of individual items of equipment - try fitting a shaver socket within zones in a bathroom that doesn't have a separating transformer or a class I item in a pool where 702.55.4 called for class II. In these cases the choice of individual items is critical to the overall compliance of the system to BS 7671 - and straight ADS isn't permitted.

Aside from the 'ignore the internals of single items of equipment' debate, there are times where we construct a system from several components and cables (e.g. transformer powered door bell, SELV heating controls (e.g. HeatMister network ones), intruder alarm systems etc - although not "mains" they're clearly within the scope of BS 7671. Tradition seems to stop at the FCU and just brush everything after that under the carpet - but there doesn't seem to be a logical justification for that (other than it's convenient for the hard pressed electrical inspector, of course).

Then you have areas (e.g. non-domestic) where c.p.c.s aren't demanded to class 2 equipment, you could, for argument's sake, wire an extension to a lighting circuit in an insulated wiring system, no c.p.c. and double-insulated light fittings. Not the entire installation, not the entire circuit, just the addition. It doesn't seem that logical to then tick the ADS box.

- Andy.
 23 April 2013 09:59 PM
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leckie

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I think that the ESC questions and answers bit also says that when fitting a shaver socket, that the electrical separation box should not be ticked..
Can't find the link to it, but I know I have read it.

I think we need the regs, guidance notes, guidance on the guidance notes and a little further guidance. I'm from Irish extraction and I like to be sure to be sure.
 24 April 2013 09:11 AM
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Parsley

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Originally posted by: leckie

I think that the ESC questions and answers bit also says that when fitting a shaver socket, that the electrical separation box should not be ticked..

Can't find the link to it, but I know I have read it.



I think we need the regs, guidance notes, guidance on the guidance notes and a little further guidance. I'm from Irish extraction and I like to be sure to be sure.



ESC website industry section places of work new installations

Q3.16

An installation uses Automatic Disconnection of Supply (ADS) as a protective measure against electric shock. An electric shaver is supplied using electrical separation through a shaver supply unit. On the schedule of inspections, should the "electrical separation" box for fault protection as a method of protection against electric shock be ticked?



No. That part of the Schedule of Inspections is intended for use when a part of an installation relies specifically on that method of protection.


I've been informed that the NIC's engineer ticks the box for double insulation where there's a class 2 light fitting on the NIC's I&T DVD. I have forsaken the pleasure but my sources are reliable.

Regards
 24 April 2013 09:48 AM
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AJJewsbury

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when a part of an installation relies specifically on that method of protection.

So isn't electrical equipment in zone 2 part of the installation?

It's all sounding rather like the Phlogiston theory - "everyone" says we should tick the ADS box alone, but the explanations as to why never seem to be quite 100%.

- Andy.
IET » Wiring and the regulations » Double Insulation

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