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
<< 11 12 13 14 15 16 17 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.
 11 January 2013 01:10 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11553
Joined: 13 August 2003

Originally posted by: Parsley

411.1 states



"Automatic disconnection of supply is a protective measure in which:

(i) basic protection is provided by basic insulation of live parts or by barriers or enclosures, in accordance with Section 416, and

(ii) fault protection is provided by protective earthing, protective equipotential bonding and automatic disconnection in case of a fault, in accordance with Regulations 411.3 to 6.



Where this protective measure is applied, Class II equipment may also be used."




The EIC protective measures section states protective measures against electric shock basic and fault protection.

In normal installations this cannot be by Double or renforced alone ADS is still required.



Maybe another box should be added to the fault protection section for double or reinforced insulation, like the class II box under indirect contact in the 16th.



Regards


I'm not following your logic here - double/reinforced insulation does provide both basic and fault protection against electric shock - that's the nature of it.

412.1.3 seems to be causing a lot of confusion - I just read it as saying that double insulation can't (in common circumstances) be used to the exclusion of everything else - i.e. you still need to provide facilities for class 1 equipment to be connected.

Installing double insulated equipment on an circuit that supports ADS doesn't in my mind magically transform that equipment into class 1.

- Andy.
 11 January 2013 01:23 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19747
Joined: 23 March 2004

I'm not following your logic here - double/reinforced insulation does provide both basic and fault protection against electric shock - that's the nature of it.


It does Andy - I agree entirely.

412.1.3 seems to be causing a lot of confusion - I just read it as saying that double insulation can't (in common circumstances) be used to the exclusion of everything else - i.e. you still need to provide facilities for class 1 equipment to be connected.


two points

1- the regulation dosn't preclude parts of the circuit or equipment being DI - ie Class 2 luminaires for example.

2 - The reg does require where it's the sole means of protection that the limitations on what may be connected plus the requirements for supervision etc are met as you say. That alone tells me that i cannot be making a claim on it as designer in a "normal installation" even if it's wire in singles in plastic conduit and uses class 2 luminaires. I'd still need that CPC, even if i don't use it the system is now ADS - as we have a CPC present.

Installing double insulated equipment on an circuit that supports ADS doesn't in my mind magically transform that equipment into class 1.


It doesn't make it class 1 - but in your own words it's ADS (particularly as all the other requirements for DI aren't met usually.

regards

OMS

-------------------------
Failure is always an option
 11 January 2013 01:33 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11553
Joined: 13 August 2003

the system is now ADS - as we have a CPC present.

That's what I don't follow. To my mind the system has both DI and ADS parts - it's no solely ADS. The DI bits don't stop being DI because there's a c.p.c. somewhere in the vicinity. If we needed to inspect them for DI when they were DI alone, surely we'd need to do the same inspections on the DI bits within a mixed DI and ADS system?
- Andy.
 11 January 2013 01:34 PM
User is offline View Users Profile Print this message


Avatar for colinhaggett.
colinhaggett

Posts: 365
Joined: 08 July 2004

Originally posted by: daveparry1

I will just add that I can't remember ever ticking "the box" and i've never had it mentioned to me on niceic yearly assessments!



Dave.


And they've never said anything to me for ticking "the box"on NICEIC assessments. I only tick when using double insulated lights etc. Maybe am totally wrong. Would be nice to see what the NICEIC view on this on their forms. Seems to me form this debate that if we can't agree it rather needs explaining.

 11 January 2013 01:38 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19747
Joined: 23 March 2004

Originally posted by: AJJewsbury

What is the method of protection from direct and indirect contact ?. We have insulated lampholders with no CPC.


I would have guessed that direct contact is prevented by basic insulation.

It is.

To me "indirect contact" doesn't really make sense in the case of the 2-core pendent flex & lampholder - there being no metalwork that could be made live by a fault to make contact with. I guess the new "protection against shock under fault conditions" is a better description in that case - i.e. should the basic insulation fail for any reason.

OK - I can go with that - a fault free zone perhaps would be another description as indicated in the final sentence of 411.3.1.1 and not having an exposed conductive part


Compared with the old twisted-twin setup (which is of course no longer acceptable), it seems to me it's the flex sheath that provides the 2nd line of defence - we could argue whether it's action is to prevent people touching the (potentially failed) basic insulation (a kind of barrier), acting as a second layer of electrical insulation (like double insulation) or it's just physical protection to prevent the basic insulation being (mechanically) damaged in the first place. (My thinking is that 412.2.4.1 is suggesting we take the middle option). What I don't get is how the sheath makes automatic disconnection happen.

OK - my thinking is that the sheath is actually acting to provide protection to the insulated cores - in the same way T&E does. selection and erection rather than double insulation. The installation however is ADS

- Andy.


Regards

OMS

-------------------------
Failure is always an option
 11 January 2013 01:41 PM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 1039
Joined: 04 November 2004

Andy

I don't think I said that double and reinforced insulation doesn't' provide basic and fault protection.

Double and reinforced can't be relied on as the only method in a normal installation, as you point out in your last post i.e ADS is still required and will be the method ticked for fault protection.

The EIC's first set of boxes are for basic and fault protection. In a controlled installation the box could be ticked, if that's what the designer specifies, but not in a normal installation because ADS will still be required.

Regards
 11 January 2013 01:49 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19747
Joined: 23 March 2004

Originally posted by: AJJewsbury

the system is now ADS - as we have a CPC present.


That's what I don't follow. To my mind the system has both DI and ADS parts - it's no solely ADS. The DI bits don't stop being DI because there's a c.p.c. somewhere in the vicinity. If we needed to inspect them for DI when they were DI alone, surely we'd need to do the same inspections on the DI bits within a mixed DI and ADS system?

- Andy.


The system has DI present, yes - we just can't make a claim on it because all of the other requirements are not met. So that only leaves us ADS and insulation of live parts. So generally box 5 (probably 6) and the first 4 boxes under ADS.

Regards

OMS

-------------------------
Failure is always an option
 11 January 2013 01:52 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11553
Joined: 13 August 2003

Double and reinforced can't be relied on as the only method in a normal installation, as you point out in your last post i.e ADS is still required and will be the method ticked for fault protection.

A methods I could understand, but why the (only) method? Why can't I tick both, if both are present?
- Andy.
 11 January 2013 01:54 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11553
Joined: 13 August 2003

The system has DI present, yes - we just can't make a claim on it because all of the other requirements are not met.

What other requirements?
- Andy.
 11 January 2013 02:03 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19747
Joined: 23 March 2004

Originally posted by: AJJewsbury

Double and reinforced can't be relied on as the only method in a normal installation, as you point out in your last post i.e ADS is still required and will be the method ticked for fault protection.


A methods I could understand, but why the (only) method? Why can't I tick both, if both are present?

- Andy.


If all the requirements for DI are present Andy, in an installation that also contains ADS circuits, then yes you would, and elaborate on a seperate schedule

regards

OMS

-------------------------
Failure is always an option
 11 January 2013 02:54 PM
User is offline View Users Profile Print this message



rogersmith7671

Posts: 886
Joined: 04 November 2004

On the old Nic Eic 16th pro-forma earthed equipotential bonding and Automatic Disconnection of Supply could be declared in a little box all of its own under particulars of the installation at the origin. The IEE ones where different in that there was no separate box. EEBADS was assumed and given in the shedule of inspections in sub-section 3 (i), on page 296 BS7671:2001 (16th)
Things changed in 2008 when the 17th edition came into current use the Nic Eic retained the little box but changed the question from; method of protection against indirect contact to protective measures against electric shock so that ADS could be decared or reported.
The current Iet (17th) forms still don't have a box in the equivalent section and EEBADS is not given nor is ADS, this is because of a change in the way that the methods of protection against electric shock are refered to.
Odly the DPC for the 17th uses the old pro-forma, the new one appeared after the period of public disscusion ended.

Regards
 11 January 2013 09:36 PM
User is offline View Users Profile Print this message


Avatar for leckie.
leckie

Posts: 1872
Joined: 21 November 2008

Well like I said earlier, the system is ADS, that is giving basic and fault protection.

If you attach a class 2 fitting onto that system you do need to tick a box to confirm that it is installed correctly, the box you tick that confirms that the class 2 fitting is fitted correctly is " correct connection of accessories and equipment".

That's it, that's all you have to do.

Well, that is until someone disagrees, but that's what I think.
 12 January 2013 04:56 PM
User is offline View Users Profile Print this message



weirdbeard

Posts: 1579
Joined: 26 September 2011

Originally posted by: Zs





I'm sat here checking a ream of installation certificates which relate to a commercial building and have been issued by the installer prior to my inspection. They are mostly for replacement DBs.


In the first section of the schedule of inspections, method of protection against electric shock, the installer has ticked the boxes for Double Insulation and Reinforced insulation.



I'm inclined to get him to untick those boxes. Do you agree?




Hi, just a thought, not sure if anyone has mentioned this, but if an EIC has been issued for the replacement of a DB, wouldn't this be ticked as an alteration to an existing installlation in the DESCRIPTION AND EXTENT OF THE INSTALLATION section, which also has tick boxes for additions and new installations.......


........The tick box page entitled SCHEDULE OF INSPECTIONS clearly says: (for new installation work only)....

So wouldn't it be fair to say that in section H of an EIC that is for additions or alterations to an existing installation the number of inspection schedules required is zero ?
 12 January 2013 05:34 PM
User is offline View Users Profile Print this message



rogersmith7671

Posts: 886
Joined: 04 November 2004

let's say that the alterations box has been ticked and the description and extent of the EIC is limited to the DB's only. a schedule of items inspected may still be required, albeit limited to the actual work done and not the whole existing installation (some will argue that the entire installation must be inspected and test though). Most of the boxes would then be N/A. On the basis that the DB change would need some inspection and reporting.

regards
 12 January 2013 05:47 PM
User is offline View Users Profile Print this message



weirdbeard

Posts: 1579
Joined: 26 September 2011

Originally posted by: rogersmith7671

let's say that the alterations box has been ticked and the description and extent of the EIC is limited to the DB's only. a schedule of items inspected may still be required,


Hi roger, it looks pretty clear to me:

The tick box schedule of inspections page says "(For new installation work only)"

If the new installation box on page is not ticked there need be no schedules of inspections attached to the certificate????
 12 January 2013 05:51 PM
User is offline View Users Profile Print this message



rogersmith7671

Posts: 886
Joined: 04 November 2004

Oh right, i hadn't noticed that.. but do you mean the one in the "regs" or the Nic Eic one?

regards
 12 January 2013 05:55 PM
User is offline View Users Profile Print this message



weirdbeard

Posts: 1579
Joined: 26 September 2011

Hi Rog, from the ammended forms on this site.
 12 January 2013 06:03 PM
User is offline View Users Profile Print this message



rogersmith7671

Posts: 886
Joined: 04 November 2004

Well spotted! Whether this solves the argument though, is another matter.

Regards.
 12 January 2013 06:04 PM
User is offline View Users Profile Print this message



weirdbeard

Posts: 1579
Joined: 26 September 2011

So, I guess my question to ZS is - was the new installation box ticked on the EIC - if not then the schedule of inspections is itself wrong! ???
 12 January 2013 06:16 PM
User is offline View Users Profile Print this message



rogersmith7671

Posts: 886
Joined: 04 November 2004

Oh wow, what a bust! hundeds of posts to this thread later and the real answer wasn't a tick but "none of the above". Ah well we live and learn, should have read the question more closely.
Good one, weirdbeard!

Regards.
IET » Wiring and the regulations » Double and reinforced insulation

<< 11 12 13 14 15 16 17 Previous Next Last unread
Topic Tools Topic Tools
Statistics

See Also:



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