IET logo
 
IET
Decrease font size
Increase font size
Topic Title: Double and reinforced insulation
Topic Summary: Definition
Created On: 31 December 2012 12:11 PM
Status: Post and Reply
Linear : Threading : Single : Branch
<< 13 14 15 16 17 18 19 Previous Next Last unread
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 13 January 2013 11:33 PM
User is offline View Users Profile Print this message


Avatar for leckie.
leckie

Posts: 1605
Joined: 21 November 2008

As I said, I think it about the perspective from which you view it. I cant see what the preoccupation of ticking that box is. I think OMS and RnR have it sorted.

In the mean time I will leave the boxes saying n/a and make sure I check that the DI kit fitted onto the ads install is all wired and installed properly. And I'll tick the box, correct connection of equipment, in my mind that sorts it. None of the cables are, IMO, double insulated. They just become part of of the wiring system if part of a designed double insulated installation. You have to connect it together with something.
 13 January 2013 11:42 PM
User is offline View Users Profile Print this message


Avatar for leckie.
leckie

Posts: 1605
Joined: 21 November 2008

Out of interest, has anyone ever had a comment from an niceic, eca, elseca, napit, assessor? I haven't and I've been having them for over 30 years. So perhaps it's not that important really. But it's nice to know!
 14 January 2013 05:11 AM
User is offline View Users Profile Print this message


Avatar for spinlondon.
spinlondon

Posts: 4409
Joined: 10 December 2004

Is that your answer Keith, keep taking the tablets?
What a cop out.
 14 January 2013 03:45 PM
User is offline View Users Profile Print this message


Avatar for kj scott.
kj scott

Posts: 2144
Joined: 02 April 2006

Originally posted by: AJJewsbury

BS 6004 meter tails are insulated and sheathed; as is twin and earth; they are not double insulated and BS 7671 does not say that they are; Note 1 to Regulation 412.2.4.1 states 'However it is considered that the insulation of the cabling system is at least equivalent to the requirement in BS EN 61140 for reinforced insulation'.


Presumably T&E cables etc are acceptable under BS 7671's requirements for protection against electric shock - so they must comply with chapter 41 - specifically one (or more) of sections 411, 412, 413 or 414 (for ordinary circumstances).

There is no specific section for 'insulated & sheathed' in chapter 41.

While T&E may be part of a ADS system (and so you'd need to check ADS requirements for the sake of any connected class 1 equipment), it clearly can't use ADS itself to protect against electric shock (as they're no earthed metal between live conductors and the victim, so if there's no other protection then there's nothing to stop someone getting a shock if the basic insulation of the cable fails). So as far as the T&E cable is concerned, that's 411 out. For directly connected mains circuits 413 and 414 clearly don't apply either. That leaves just 412.

412.2.4.1 says T&E cable (and others) comply with section 412.

So when we come to inspecting T&E cable (or PVC conduit etc), which section's requirements should we checking against? I say it should be 412.

When we record that an inspection has been carried out to verify the requirements of 412, which box(es) should be ticked? I'd say Double/reinforced insulation.

Where am I going wrong?

- Andy.


BS 7671 does not require a conductor to be double insulated, only single insulated with mechanical protection. If the installation is suitably designed, constructed and maintainedtheir should be no reason for the basic insulation to fail.

-------------------------
http://www.niceic.biz
 14 January 2013 03:53 PM
User is offline View Users Profile Print this message


Avatar for kj scott.
kj scott

Posts: 2144
Joined: 02 April 2006

Originally posted by: spinlondon

Is that your answer Keith, keep taking the tablets?

What a cop out.


'Oh yes Keith.
Not only does Note 1 of 412.2.4.1 indicate that the insulation of the cabling system is at least equivalent to reinforced insulation (reinforced being equivalent to double), the body of the text of the Regulation indicates that a wiring system installed in accordance with Chapter 52 is considered to meet the requirements of Regulation 412.2 (i.e. provide both basic and fault protection'

Its like the car advertisement, sounds just like a VW, but it isn't.

-------------------------
http://www.niceic.biz

Edited: 14 January 2013 at 04:04 PM by kj scott
 14 January 2013 03:55 PM
User is offline View Users Profile Print this message


Avatar for kj scott.
kj scott

Posts: 2144
Joined: 02 April 2006

Originally posted by: leckie

Out of interest, has anyone ever had a comment from an niceic, eca, elseca, napit, assessor? I haven't and I've been having them for over 30 years. So perhaps it's not that important really. But it's nice to know!


What sort of comment would you be looking for leckie?

-------------------------
http://www.niceic.biz
 14 January 2013 04:02 PM
User is offline View Users Profile Print this message


Avatar for kj scott.
kj scott

Posts: 2144
Joined: 02 April 2006

Originally posted by: John Peckham

I don't think there is a definite answer to the question of to tick or not to tick the box just opinion. I think provided you can give YOUR sound reasoning to why YOU have ticked the box that is fine. The problem arises if under scrutiny you cannot give a reason with a sound explanation. In Zs case if the inspector has ticked the box and there is no Class 2 equipment present then that is a minor issue as no doubt there will be more critical issues for her to report.

John, if the item is present, then tick the box, I would say that's definite enough. In Zs' case hasn't the inspector gone AWOL.

For information and the avoidance of doubt I am a box ticker if Class 2 equipment is present on an ADS installation. My report , my signature.


I would agree with the responsibility of the inspector as well though.

-------------------------
http://www.niceic.biz
 14 January 2013 04:59 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 10964
Joined: 13 August 2003

BS 7671 does not require a conductor to be double insulated, only single insulated with mechanical protection. If the installation is suitably designed, constructed and maintainedtheir should be no reason for the basic insulation to fail.

Really? Where does it say that?

If that's the case, I can put singles in metal conduit without bothering to earth the conduit then? The steel conduit simply needs to provide mechanical protection? (Which it would do just as well as PVC conduit).

- Andy.
 14 January 2013 05:52 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 18919
Joined: 23 March 2004

416 and 417 essentially.

It's only 521.10.1 that makes a requirement for single insulated cables to be enclosed.

If that containment is metallic then we have an exposed conductive part which requires earthing.

BS 7671 allows us to provide bare conductors subject to a few basic precautions

Regards

OMS

-------------------------
Failure is always an option
 14 January 2013 08:56 PM
User is offline View Users Profile Print this message


Avatar for leckie.
leckie

Posts: 1605
Joined: 21 November 2008

Originally posted by: kj scott

Originally posted by: leckie



Out of interest, has anyone ever had a comment from an niceic, eca, elseca, napit, assessor? I haven't and I've been having them for over 30 years. So perhaps it's not that important really. But it's nice to know!




What sort of comment would you be looking for leckie?


I merely asked what comment anyone may have received from an assessment. I have never had any comment made for not ticking the box that you think needs ticking. I wondered if anyone else had.

And I will not tick a box just for connecting a bit of kit onto an ads protected system. Oh sorry I'm wrong. I will tick a box, just not the DI box. Only the one to say I've connected equipment correctly. Because that's all you need to do.
 14 January 2013 09:33 PM
User is online View Users Profile Print this message



daveparry1

Posts: 5882
Joined: 04 July 2007

As I said a few days ago I can't ever remember ticking that box and it has never been mentioned on nic annual assessments,

Dave.
 14 January 2013 09:38 PM
User is offline View Users Profile Print this message



Zs

Posts: 2629
Joined: 20 July 2006

Hello,

I have deliberately not read today's posts and I will look at them in a few minutes.

I've been there today. On the way home I thought about you and checked in with my real self. Not the self who is being paid to criticise this installation to the client. The client knows nothing of Zs. I can tell it as it is to you.

So, in fairness, in terms of new circuits; If you walked in there tomorrow and looked for the fault, it isn't so bad..We see a great deal worse. It is just a standard installation of some new distribution boards and some circuits. Albeit you had better brace yourself because there are some things I am going to tell you which are going to make you hair curl.

What I see there are all the signs of an installer who has underpriced his job and been put under pressure.

But, and here is the big but; His certificates are apalling and in truth they are shameful. His creativity and inventiveness with distribution throws me into a quandry between him earning food for his family and a shooting at dawn.

It says TNCS and it is a TNS. A bit of witness testing is evidence of some fictional numbers created by someone who doesn't know how to create fictional numbers. A bit of experience, once I'd seen the length of the circuits, told me of the fiction before even opening the pilot's bag I took with me with some essential test kit in it. IMHO there is something very important which comes from being an installer as well as an inspector and it comes from the gut.

Connections are fine, the new circuits are in fact many and are boringly average just like you or I would do, cabling is appropriate, the switching on the circuits is altogether normal.

But it is scrappy and you can see the haste when you go inside the boards. I'd say this man is broke and had an opportunity for a quick buck if he pulled his weight. Sadly I think he is punching above his weight and needs to slow down and think.

There are three boards out of the ten which may be home made. They are on the certificates as 230/4000 (sic) volts, double and reinforced insulation, Felv, undervoltage protection ticked and N/A for choice and setting of protective and monitoring devices. They are three phase and neutral, protected by a single RCD each. The front cover is a cut out rectangle of 3mm mild steel which has been beautifully cut to fit over the breakers and the RCD. Each board has at least 15 breakers and then a single breaker in it which is not RCD protected and is piggy-backed from the incoming supply to the breaker. Switching off the RCD does not switch off the supply to the rogue breaker. You curling yet?

The order of L1/L2/L3 is all over the place. Only in these three boards though. The rest are better than mine. I have to say that because it is true.

The three phases and the neutral come in through drilled holes in the side of the boards with no grommet, gland or bush. Ooh la, no grommet gland or bush, write it down and get him to buy some. But he'd have had to buy two for each because he's brought his neutral in one one side and his phases in on the other. One of these examples is in the main incoming control panel and is not remote via a good length of SWA but is about 30 cm from the main cut out switches. Not that it really makes a difference.

There is a lighting circuit (existing) with 50 aged egg box lights on it which I am told 'used to work perfectly before he came in'. May I say out loud that it is tempting to jump to the defence of our fellow installer when we hear words like that..'He' or 'She'. Anyway, each fitting has 4 x 2 foot lamps so 4 x about 18W fluorescents fifty times I'd say. They switch them on in the morning by leaning on every switch at once, that is a question I learned to ask from you OMS so I thank you for that. I expect that is contributing to their tripping problem on one of the boards. It is on the certifcates as having a Zs of 1.34. Reality is quite different and quite massive.

And so on. But we really do see worse out there. This one does not smell of burning.

Double insulation? Not on your nelly x2. It is egg box lighting throughout including the cleaners' cupboards and the toilets. The closest I can offer you to any definition of double insulation is a plastic extractor fan in what used to be their smoking room and is now not used. That's not my definition as you know but it is only fair to tell you that it is there.

So, here I am back at Zs towers and absolutely crackered. With a handsome offer to put it all right manually, I am only an average installer so I declined that in favour of the consultancy and a report explaining the issues.

You know that London theatre I talk about on here? Well, for the past year I have been walking them slowly through their installation which was far more dangerous than today's. I'm at the theatre tomorrow as it happens. I tell them what is wrong and I write 'this means that' on lots of bits of paper . Twelve months and they are now very close to the word 'satisfactory'.

That is why I do this.

I thank you.


Zs
 15 January 2013 11:01 AM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 18919
Joined: 23 March 2004

It sounds like a typical install undertaken by someone without a lot of understanding of the system being worked on, some craft skills but not enough to be safe and undertaken against severe time or cost pressure

Essentially by an installer who can probably work well under someone else direction but with no real design savvy and willing to cut corners (perhaps inadvertantly) to get to the deadine.

There'll be a million of them across the UK alone.

Will anyone die - probably not. Will the next guy doing a EICR have a field day - probably. Will the client look back and decide to persue matters - maybe.

His creativity and inventiveness with distribution throws me into a quandry between him earning food for his family and a shooting at dawn.


For sure - it happens all the time. If I may offer a bit of advice based on a few years of being in similar situations.

1 - be clear on who your client is - and where your obligations are directed.

2 - be as objective as you can - if there is a regulation breached then say so - don't offer the solution in the report. If it's a matter of opinion, or "I wouldn't do it that way" then stop and perhaps get a second opinion - explain the reasoning in the report.

It's about being reasonable and not making it personal whilst recognising that there are real persons involved in it.


reverse the situation in your mind perhaps - if it was your install and the installer was acting as the client rep on this how kind would you expect them to be to you.

On balance though, I suspect the report to raise enough problems based on what you've seen that remedials are required and that will raise the thorny issue of money. Somewhere that'll need some design.

so I declined that in favour of the consultancy and a report explaining the issues.


Very wise - good luck with it.

Regards

OMS

-------------------------
Failure is always an option
 15 January 2013 01:22 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 10964
Joined: 13 August 2003

416 and 417 essentially.

Sorry OMS, I'm still not following. 416 is just about basic protection - as i read it, it needs to be used in conjunction with your chosen method(s) of protection against shock - i.e. one or more of 411-414, as 410.3.3 says. E.g. 411.2 says you need to comply with 416 or 417 to provide basic protection that ADS (partly) relies on. Reading 410, I don't get the impression that the intention is that you could comply with 416 alone.

As I see it, 410.3.3 says in general that each (and every) part of the installation needs to comply with one (or more) of 411 (ADS), 412 (double/reinforced insulation), 413 (separation) and 414 (SELV/PELV) - I presume that wiring systems are part of the installation and I don't see an exemption from 410 for them.

It's only 521.10.1 that makes a requirement for single insulated cables to be enclosed.

Not only, but also I'd suggest. (Although I'm not convinced bell wire, on a SELV bell circuit, really needs to be sheathed/enclosed...)

If that containment is metallic then we have an exposed conductive part which requires earthing.

But that pre-supposes that something more than basic protection + mechanical protection is required - which is my point! Earthing is only demanded by 411 - it's not a universal principle. 412 wouldn't let the situation arise, 413 demands it's not earthed, likewise 414.

- Andy.
 15 January 2013 02:22 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 18919
Joined: 23 March 2004

Originally posted by: AJJewsbury

416 and 417 essentially.


Sorry OMS, I'm still not following. 416 is just about basic protection - as i read it, it needs to be used in conjunction with your chosen method(s) of protection against shock -

Yes - for basic protection, ie direct contact shock - all you need is a single layer of insulation or none at all if you put the conductors inside boxes, up high - or out of reach. It's used as part of the measure of protection under normal conditions.

i.e. one or more of 411-414, as 410.3.3 says. E.g. 411.2 says you need to comply with 416 or 417 to provide basic protection that ADS (partly) relies on. Reading 410, I don't get the impression that the intention is that you could comply with 416 alone.

Used in conjunction with, yes - but the method then addresses fault (or indirect contact) - see 410.3.2


As I see it, 410.3.3 says in general that each (and every) part of the installation needs to comply with one (or more) of 411 (ADS), 412 (double/reinforced insulation), 413 (separation) and 414 (SELV/PELV) - I presume that wiring systems are part of the installation and I don't see an exemption from 410 for them.

I agree Andy - or any combination of those to achieve both basic and fault protection.


It's only 521.10.1 that makes a requirement for single insulated cables to be enclosed.


Not only, but also I'd suggest. (Although I'm not convinced bell wire, on a SELV bell circuit, really needs to be sheathed/enclosed...)

What other regulation requires it - basic protection is simply a single layer of insulation - what you use for fault protection is up to the designer. If it's ADS, then yes, we have an exposed conductive part - so the singles in conduit is as a result of an installation method - 521.10.1 - it could remain unearthed depending on the method adopted for fault protection.


If that containment is metallic then we have an exposed conductive part which requires earthing.


But that pre-supposes that something more than basic protection + mechanical protection is required - which is my point! Earthing is only demanded by 411 - it's not a universal principle. 412 wouldn't let the situation arise, 413 demands it's not earthed, likewise 414.

OK - I'm with you now - yes, we need simple insulation (or none at all) or be at a sufficiently low voltage, coupled with a method for protection against indirect contact - which isn't what keith said originally was it ?

basic protection only provides protection when no fault is present - which I suspect is where Keith was coming from - fault protection assumes a fault is present. Mechanical protection is aimed at keeping that basic insulation intact



- Andy.


It's gonna be a mammoth thread this one for sure -

regards

OMS

-------------------------
Failure is always an option
 15 January 2013 02:47 PM
User is offline View Users Profile Print this message


Avatar for weirdbeard.
weirdbeard

Posts: 1372
Joined: 26 September 2011

Originally posted by: OMS


It's gonna be a mammoth thread this one for sure -



Agreed, it is an interesting one though!

If there has been an eic produced for a DB swap, and there is presumably a schedule of inspections, and a related schedule of test results for the DB,but how can the schedule of inspections be properly filled out?

Theres a tick box for proper routing of cables in safe zones, yet this cannot be reasonably ticked for cables in an existing installation, and the box must be marked either tick or N/A? Theres no allowance for LIM on an EIC schedule of inspections.
 15 January 2013 02:50 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 18919
Joined: 23 March 2004

Well, for a Dist Bd swap, no cables have been installed so it isn't part of the scope of that EIC - so not applicable I suspect is the correct way don't you think

regards

OMS

-------------------------
Failure is always an option
 15 January 2013 02:53 PM
User is offline View Users Profile Print this message


Avatar for weirdbeard.
weirdbeard

Posts: 1372
Joined: 26 September 2011

Just another thought, where the are mcbs sticking out a DB cover theres not much plastic seperating the user from the electric - so MCB casings can count as reinforced insulation?
 15 January 2013 02:57 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 18919
Joined: 23 March 2004

Originally posted by: weirdbeard

Just another thought, where the are mcbs sticking out a DB cover theres not much plastic seperating the user from the electric - so MCB casings can count as reinforced insulation?


Are they marked as such ?

regards

OMS

-------------------------
Failure is always an option
 15 January 2013 03:09 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 10964
Joined: 13 August 2003

What other regulation requires it

412.2.4.1 (ii)(b) for 412 for one.

I can't find it explicitly stated under 411, but common sense suggests to me that for ADS to provide protection against electric shock, there must be an exposed-conductive-part between live conductors and any likely victim - implying earthed conductive trunking, conduit, or enclosure would be needed to surround basic-insulation-only conductors for ADS to work.

Theres a tick box for proper routing of cables in safe zones, yet this cannot be reasonably ticked for cables in an existing installation, and the box must be marked either tick or N/A? Theres no allowance for LIM on an EIC schedule of inspections.

If the cables haven't been newly installed then they're not covered by the certificate (we only certify what we've done, existing can only be reported on (e.g. using an EICR)). For a simple DB change there would be no new concealed cables, the 'extent of installation covered by this certificate' box would be filled in to indicate that it applied to the DB only, and so N/A in the routing of cables box would be appropriate.
- Andy.
IET » Wiring and the regulations » Double and reinforced insulation

<< 13 14 15 16 17 18 19 Previous Next Last unread
Topic Tools Topic Tools
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.