IET logo
 
IET
Decrease font size
Increase font size
Topic Title: Time on from AMD3 and enclosures
Topic Summary: was it ever 'bottomed' out
Created On: 20 March 2017 04:06 PM
Status: Read Only
Linear : Threading : Single : Branch
1 2 3 4 5 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.
 20 March 2017 04:06 PM
User is offline View Users Profile Print this message



psychicwarrior

Posts: 514
Joined: 18 October 2010

Good day all

Was reading this thread and got to later post mentioning AMD3 and earthing etc : http://www.theiet.org/forums/f...=102648&enterthread=y

And then came across this one: http://www.theiet.org/Forums/f...id=205&threadid=62697

I apologise in advance if I have missed any industry news or comment on this forum that answers my question.

What's the view/instruction - do the AMD3 related regs ("similar switchgear") on enclosures apply to those units holding for example just an DP switch&fuse, or for that matter a TT RCD as mentioned in the link posts, or the PV isolator - or can they still be plastic (or any other non BS EN 61439 3) ?
 20 March 2017 04:13 PM
User is offline View Users Profile Print this message



geoffsd

Posts: 1521
Joined: 15 June 2010

If you look at the definition in Part 2 of 'switchgear' you may be able to decide - assuming the authors of 421.1.201 also did that.
 20 March 2017 05:14 PM
User is online View Users Profile Print this message



AJJewsbury

Posts: 15419
Joined: 13 August 2003

I'm still of the opinion that a DP switch and a fuse in an enclosure would be switchgear (practically identical to a 1-way CU), but any single device (RCCB or switch disconnector, rotary isolator even) isn't.

Likewise a simple lightswitch isn't switchgear.

The one to test the definitions with is a 13A switched fused connection unit...

AKAIK the official guidance on steel CUs is still in the pipeline.

- Andy.
 21 March 2017 09:06 AM
User is offline View Users Profile Print this message



gkenyon

Posts: 4896
Joined: 06 May 2002

Originally posted by: AJJewsbury

I'm still of the opinion that a DP switch and a fuse in an enclosure would be switchgear (practically identical to a 1-way CU), but any single device (RCCB or switch disconnector, rotary isolator even) isn't.
Except where the RCD or the like is housed in a BS EN 61439-compliant enclosure (the title of the standard gives that one away, sadly).


Likewise a simple lightswitch isn't switchgear.
Functional switching ... electrical accessories standards ...



The one to test the definitions with is a 13A switched fused connection unit...
to BS 1363-5, so not "switchgear"

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 21 March 2017 09:48 AM
User is online View Users Profile Print this message



AJJewsbury

Posts: 15419
Joined: 13 August 2003

Except where the RCD or the like is housed in a BS EN 61439-compliant enclosure (the title of the standard gives that one away, sadly).

I don't quite follow the logic there Graham - just because a component is suitable for use as switchgear doesn't necessarily mean it will be switchgear when used for (slightly) different purpose. As an extreme example, I'm sure that no-one would object to an old bakalite Wylex Cu being used as a door stop - even if it complies with the standard for CUs it's still being used as a door stop, not a CU, so no need for it to have a fireproof enclosure etc. Surely when reading BS 7671 it's BS 7671's definition of switchgear that counts - i.e. "An assembly of main and auxiliary switching equipment for operation, regulation, protection or other control of an electrical installation." - if it contains only a single switching device then it can't have "main and axiliary" switching so fails the test.

- Andy.
 21 March 2017 12:14 PM
User is offline View Users Profile Print this message



gkenyon

Posts: 4896
Joined: 06 May 2002

Originally posted by: AJJewsbury

Except where the RCD or the like is housed in a BS EN 61439-compliant enclosure (the title of the standard gives that one away, sadly).


I don't quite follow the logic there Graham - just because a component is suitable for use as switchgear doesn't necessarily mean it will be switchgear when used for (slightly) different purpose. As an extreme example, I'm sure that no-one would object to an old bakalite Wylex Cu being used as a door stop - even if it complies with the standard for CUs it's still being used as a door stop, not a CU, so no need for it to have a fireproof enclosure etc. Surely when reading BS 7671 it's BS 7671's definition of switchgear that counts - i.e. "An assembly of main and auxiliary switching equipment for operation, regulation, protection or other control of an electrical installation." - if it contains only a single switching device then it can't have "main and axiliary" switching so fails the test.



- Andy.
I agree with you ... but I don't see how a single 2-pole RCD in a Switchgear enclosure with related terminals for earth, is not an "assembly", and is therefore not "Switchgear": I think it is.

Or are you saying that a definition that includes the word "circuits" doesn't apply to a single circuit?

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 21 March 2017 01:11 PM
User is offline View Users Profile Print this message



gkenyon

Posts: 4896
Joined: 06 May 2002

The discussion does, however, highlight, something important.

Whilst I still think that the RCD for the shower outside the bathroom is Switchgear, I perhaps would be of the opinion that it wouldn't (at least always) have the same type of fire risk as a Consumer Unit at the origin. Similarly, a garage CU stuck on the end of a 32 A run from the main CU.

But, if you decide that the garage CU must be metal (or in a metal enclosure) to comply with the relevant Reg (say, an attached garage - I'm sure we'll have differing opinions for detached as it's not in the house, and argue over what is meant by "dwelling" ), then by the same token (in my view) you would decide that the shower RCD outside the bathroom should be in a metal enclosure?

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 21 March 2017 01:13 PM
User is online View Users Profile Print this message



AJJewsbury

Posts: 15419
Joined: 13 August 2003

I agree with you ... but I don't see how a single 2-pole RCD in a Switchgear enclosure with related terminals for earth, is not an "assembly", and is therefore not "Switchgear": I think it is.

Or are you saying that a definition that includes the word "circuits" doesn't apply to a single circuit?

I agree it's an assembly, just not an assembly containing both "main and auxiliary switching equipment" (my emphasis on and) - as so as such doesn't meet BS 7671's definition of switchgear.

- Andy.
 21 March 2017 01:16 PM
User is offline View Users Profile Print this message



mapj1

Posts: 8956
Joined: 22 July 2004

if it did, how would we consider the humble light switch, or the RCD spur - which is also an example of switchgear, but not by that definition.
It is that 'main and auxiliary' part - which excludes things that are only main switches, and things that are only auxiliary switches.
Equally I suspect cock-up wins over conspiracy, and this was not at all how it was supposed to be read at all when it was first drafted. Really there is a more serious problem with AMD3 and TT installations, and dancing about the semantics does nothing to avoid it. Even the 'glanding' kits do not really give the same coverage as ADS and double fault to danger, at least in CUs where the main switch is not an RCD, as extra anchoring of the incoming tails is all very well, but the bus bars, in RCBO designs, and the usually single insulated cores that loop L and N to the RCDS are not RCD protected either, and are not afforded the same reinforcement or mechanical protection.

Luckily, like leaving the earth wire off, or not fitting the right size fuse, an absence of ADS is only really a problem when there is a fault.

-------------------------
regards Mike
 21 March 2017 01:25 PM
User is offline View Users Profile Print this message



gkenyon

Posts: 4896
Joined: 06 May 2002

Originally posted by: AJJewsbury
I agree it's an assembly, just not an assembly containing both "main and auxiliary switching equipment" (my emphasis on and) - as so as such doesn't meet BS 7671's definition of switchgear.
The definition in BS 7671 does not include the word "both". And logically, it can't really be that case that BS 7671 definition means "both have to be present for it to be switchgear" ... otherwise most domestic CUs wouldn't come under the definition because they have no "auxiliary switching" in them ... only "main" (see definition of "Auxiliary circuit" on page 23 of BS 7671, and IEV here: http://www.electropedia.org/ie...nform&ievref=441-15-04).

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 21 March 2017 01:32 PM
User is offline View Users Profile Print this message



gkenyon

Posts: 4896
Joined: 06 May 2002

Originally posted by: mapj1

if it did, how would we consider the humble light switch, or the RCD spur - which is also an example of switchgear, but not by that definition.
How so, the light switch is a functional switch, not main switching. SImilarly, an RCD spur.

It is that 'main and auxiliary' part - which excludes things that are only main switches, and things that are only auxiliary switches.
That CANNOT be the case ... see my previous post. The "and auxiliary contacts" bit is purely to cover the (often non-domestic) side for control/monitoring.

However, for those not happy with the definition, they may be an opportunity to comment on that when the Draft for Public Comment on the 18th Edition comes out.

Equally I suspect cock-up wins over conspiracy, and this was not at all how it was supposed to be read at all when it was first drafted. Really there is a more serious problem with AMD3 and TT installations, and dancing about the semantics does nothing to avoid it. Even the 'glanding' kits do not really give the same coverage as ADS and double fault to danger, at least in CUs where the main switch is not an RCD, as extra anchoring of the incoming tails is all very well, but the bus bars, in RCBO designs, and the usually single insulated cores that loop L and N to the RCDS are not RCD protected either, and are not afforded the same reinforcement or mechanical protection.



Luckily, like leaving the earth wire off, or not fitting the right size fuse, an absence of ADS is only really a problem when there is a fault.
I wouldn't dream of commenting on this

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 21 March 2017 01:58 PM
User is offline View Users Profile Print this message



mapj1

Posts: 8956
Joined: 22 July 2004

if we want to play definition roulette "what were they thinking of "..

Switchgear

a general term covering switching devices and their combination with associated control, measuring, protective and regulating equipment, also assemblies of such devices and equipment with associated interconnections, accessories, enclosures and supporting structures

what makes us so sure that 'switching devices' by that particular definition, cannot encompass the light switch, or any other switch, like the DP isolator on my immersion heater

And the definitions that are in the other languages that I recognise are even less helpful.

My money is not on conspiracy, by the way, but the other option... so I fear we are on our own to do what is actually sensible, rather than what they asked for.

-------------------------
regards Mike
 21 March 2017 02:30 PM
User is online View Users Profile Print this message



AJJewsbury

Posts: 15419
Joined: 13 August 2003

The definition in BS 7671 does not include the word "both". And logically, it can't really be that case that BS 7671 definition means "both have to be present for it to be switchgear" ... otherwise most domestic CUs wouldn't come under the definition because they have no "auxiliary switching" in them ... only "main" (see definition of "Auxiliary circuit" on page 23 of BS 7671, and IEV here: http://www.electropedia.org/ie...&ievref=441-15-04).[/q

I'd taken "auxiliary" in it's ordinary sense of "secondary or supplementary" rather than specifically relating to auxiliary circuits (there's no mention of circuit in the definition of switchgear and no specific definition of auxiliary in BS 7671 except specifically for auxiliary circuits).

So I'd seen a typical CU as containing one manual main switch for control of the entire installation and secondary to that several automatic switching devices (fuses or MCBs) for protection.

- Andy.
 21 March 2017 03:06 PM
User is offline View Users Profile Print this message



geoffsd

Posts: 1521
Joined: 15 June 2010

There is the simpler question of whether a single switch is an "assembly".
 21 March 2017 04:02 PM
User is offline View Users Profile Print this message



gkenyon

Posts: 4896
Joined: 06 May 2002

Originally posted by: AJJewsbury

The definition in BS 7671 does not include the word "both". And logically, it can't really be that case that BS 7671 definition means "both have to be present for it to be switchgear" ... otherwise most domestic CUs wouldn't come under the definition because they have no "auxiliary switching" in them ... only "main" (see definition of "Auxiliary circuit" on page 23 of BS 7671, and IEV here:



I'd taken "auxiliary" in it's ordinary sense of "secondary or supplementary" rather than specifically relating to auxiliary circuits (there's no mention of circuit in the definition of switchgear and no specific definition of auxiliary in BS 7671 except specifically for auxiliary circuits).



So I'd seen a typical CU as containing one manual main switch for control of the entire installation and secondary to that several automatic switching devices (fuses or MCBs) for protection.



- Andy.
As mike pointed out, this is "definition roulette".

I would always consider the term Auxiliary Switching to mean the control and monitoring contacts, along with the related Auxiliary Circuits, especially when talking about Switchgear.

Originally posted by: mapj1

if we want to play definition roulette "what were they thinking of "..



Switchgear



a general term covering switching devices and their combination with associated control, measuring, protective and regulating equipment, also assemblies of such devices and equipment with associated interconnections, accessories, enclosures and supporting structures



what makes us so sure that 'switching devices' by that particular definition, cannot encompass the light switch, or any other switch, like the DP isolator on my immersion heater



And the definitions that are in the other languages that I recognise are even less helpful.



My money is not on conspiracy, by the way, but the other option... so I fear we are on our own to do what is actually sensible, rather than what they asked for.
Agreed ... but that's not the definition in BS 7671, so surely something else was meant ... or was it ??

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 21 March 2017 04:06 PM
User is offline View Users Profile Print this message



gkenyon

Posts: 4896
Joined: 06 May 2002

Originally posted by: geoffsd

There is the simpler question of whether a single switch is an "assembly".
Interesting, but the requirement for CUs talks about "similar switchgear", so we can more easily see for the purposes of that particular regulation that a light switch isn't "similar switchgear" to a CU, and a garage CU is "similar switchgear" (it's got a switch and some protective devices), but I can definitely see why Andy went down the road of perhaps considering the single RCD in an enclosure as not "similar switchgear".

(However, because the RCD enclosure is the same group of standards as the CU, that's where the counter-argument comes in, that it may, for the purposes of that reg, be considered "similar switchgear").



-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 21 March 2017 05:53 PM
User is offline View Users Profile Print this message



geoffsd

Posts: 1521
Joined: 15 June 2010

Yes, but it depends on whether you wish to rely on the words or what you think they meant when writing them.

421 says non-combustible also applies to "similar switchgear assemblies" and the definition of switchgear is "an assembly of main and auxiliary switching equipment...".

So, we have two assemblies.

A single switch in neither case constitutes an assembly.



Had 421 merely stated "similar switches" then...
 21 March 2017 06:06 PM
User is offline View Users Profile Print this message



KFH

Posts: 479
Joined: 06 November 2010

I will continue to interpret the regulations in a way that allows me to fit an RCD in a plastic enclosure by the meter if I need ADS protection on the tails and metal CU on a TT installation. The arguments above reinforce my opinion that it was a bad decision to implement metal consumer units to resolve the issue of poor connections causing fires in plastic consumer units that did not appear to meet the appropriate BS as they were lacking fire retardants in the plastic. Bring back decent screwed tunnel connections, how often did the dual screw Wylex connections fail and how often are the problems with Henly blocks with only one decent sized screw?

Fortunately, since Jan 2016, I have not had to fit tails on a TT installation long enough to require fusing as well as RCD protection as this would stretch any interpretation a bit far.

Sorry to go off topic a bit :-)
 21 March 2017 06:15 PM
User is offline View Users Profile Print this message



weirdbeard

Posts: 3022
Joined: 26 September 2011

As Gkenyon is a member of the IETs regs policy committee, and author of wiring matters articles his opinion should not be taken lightly, according to his theory REC2 type isolators found in the tails after the meter in millions of properties are a fire risk if subjected to an EICR?

-------------------------
:beer)
 21 March 2017 06:21 PM
User is offline View Users Profile Print this message



gkenyon

Posts: 4896
Joined: 06 May 2002

Originally posted by: geoffsd

A single switch in neither case constitutes an assembly.
Not sure ... what about a 2-pole isolator mounted in an EN 61439 enclosure (with associated earth terminals) ...

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
IET » Wiring and the regulations » Time on from AMD3 and enclosures

1 2 3 4 5 Next Last unread
Topic Tools Topic Tools
Statistics

New here?


See Also:



FuseTalk Standard Edition v3.2 - © 1999-2017 FuseTalk Inc. All rights reserved.

..