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Topic Title: To be an RCD brd or not to be!
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Created On: 21 September 2012 01:48 PM
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 24 September 2012 01:07 PM
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spinlondon

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Originally posted by: AJJewsbury
Spin - are you suggesting that if an existing installation exceeded BS 7671 requirements, it would not be acceptable to alter it in such a way that it merely complied with BS 7671?
- Andy.

Yes if that alteration makes the installation less safe than it was before.
BS7671 and as far as I'm aware the Building Regulations, require that any addition or alteration does not make the installation any less safe.
 24 September 2012 01:16 PM
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daveparry1

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I would say it just means should not be made any less safe than BS7671 specifies?

Dave.
 24 September 2012 01:34 PM
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AJJewsbury

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Yes if that alteration makes the installation less safe than it was before.
BS7671 and as far as I'm aware the Building Regulations, require that any addition or alteration does not make the installation any less safe.

I can see how the words could be interpreted that way, but it doesn't seem likely to be that was the intention - for instance I'd never be able to add a new light fitting as I'd be introducing a possible shock hazard (however small) that wasn't there before - thus making the installation (ever so slightly) less safe.

I'd suspect the logic is more likely to be along the lines of "if it complies, it's deemed to be safe; if it doesn't comply it should be no less safe than it was before".

- Andy.
 24 September 2012 02:26 PM
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spinlondon

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Is this another one of those cases where the actual wording of the Regulation doesn't match with the supposed intention?
From what you're saying, the requirement should just be that the addition or alteration comply with the Regulations.
Whereas in fact the requirement is not only to comply with Regulations, but also that the safety of the existing installation should not be impaired.

I think I would like to hear the logic behind your beliefs and an explanation as to why there are ten words at the end of the Regulation which needn't be there if the intent were only to ensure compliance with BS7671.

It's not so much as interpreting the words, more a case of just reading them.
I would suggest that the only time you would need to intrepet them, is if you wanted them to say somthing other than what the do say.
How exactly can you interpret the words: "and does not impair the safety of the existing installation." as anything other than what it says?
To suggest that those particular words, only mean that BS7671 should be complied with is a bit far fetched considering that the first part of the Regulation requires you do such any way.
To suggest that the second requirement is the same as the first, though it reads as being something else, is to my mind ludicrous.

Edited: 24 September 2012 at 02:38 PM by spinlondon
 24 September 2012 03:14 PM
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AJJewsbury

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Is this another one of those cases where the actual wording of the Regulation doesn't match with the supposed intention?

Well, given that the logical conclusion (e.g. you could never extent an existing installation) is clearly ludicrous, I hope so!

Whereas in fact the requirement is not only to comply with Regulations, but also that the safety of the existing installation should not be impaired.

I think I would like to hear the logic behind your beliefs and an explanation as to why there are ten words at the end of the Regulation which needn't be there if the intent were only to ensure compliance with BS7671.

I suspect it's to cover situations where a compliant addition could compromise other parts of the installation. As a random example - if I added some new sockets to a ring by extending the ring, my new wiring itself might comply with the regulations 100% (in terms of Zs, v.d. etc etc) yet the act of lengthening ring would likely increase Zs on some of the original parts of the ring, well away from the parts I was working on - I think the latter part is just reminding me that I need be mindful of that kind of thing. There are probably lots of other examples (e.g. where safety was previously ensures by methods no longer recognised by the regs - limiting R2 or mixed disconnection times for example, where new practices might be incompatible with the existing installation).

- Andy.
 24 September 2012 04:05 PM
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spinlondon

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Andy, I'm not quite sure why you need to make up these far fetched and implausible scenarios to explain what is to my mind quite an easy Regulation to understand.
The requirement to my mind is exactly as worded, make sure the work complies with the Regulations, and make sure that the installation is no less safe.
 24 September 2012 05:44 PM
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weirdbeard

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Originally posted by: spinlondon

With a new install, you can get away with it, to a degree.

You're not making an existing installation worse.

Yes there are thousands of installations that have up front RCD protection, which have never had a problem.

There are also thousands of installations where no overcurrent device has operated.

Perhaps we should do away with CUs, and just stick everything on one RCBO?

All protective devices are there just in case.

What we have to consider, is what will happen if the 'just in case' does happen.

Will it be more inconvenient if the lights go out because a dodgey appliance is plugged in to a socket?

Could it be a hazard?

If the answer is yes, then altering an installation so that inconveniance is increased would not comply with 314.1.

Altering an installation so that it introduces a hazard would not comply with both 314.1 and 610.4.


Hi spinlondon, I think you are 100% correct.

Edited: 26 September 2012 at 04:31 PM by weirdbeard
 24 September 2012 05:57 PM
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spinlondon

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A rather inane comment don't you think weirdbeard?
 24 September 2012 06:23 PM
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weirdbeard

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Originally posted by: spinlondon

A rather inane comment don't you think weirdbeard?


No, why do you think it's inane?
 24 September 2012 06:40 PM
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spinlondon

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Here's a description from an On-line dictionary

inĀ·ane [ih-neyn]

adjective
1. lacking sense, significance, or ideas; silly: inane questions.

2. empty; void.

Edited: 24 September 2012 at 09:41 PM by spinlondon
 24 September 2012 06:59 PM
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daveparry1

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Remember Spin, we don't even HAVE to comply with regs. anyway. How's that for an inane but factual statement!

Dave.
 24 September 2012 07:02 PM
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weirdbeard

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Spinlondon, many thanks for that, though I am aware of the meaning of the word, I was hoping you might be able to describe why you felt the comment was inane?
 24 September 2012 07:11 PM
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weirdbeard

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Originally posted by: daveparry1

Remember Spin, we don't even HAVE to comply with regs. anyway. How's that for an inane but factual statement!


Hi dave, agreed! In a recent topic I posted it was agreed by a very prominent forum member that it's not always actually possible to comply with the letter of the regs as they are wrote:

http://www.theiet.org/forums/f...tid=205&threadid=47815
 24 September 2012 07:33 PM
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spinlondon

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I'm begining to think, that perhaps I've stumbled onto the Screwfix forum rather than the IET's.
I can only assume from the last couple of pointless comments, that you guys have run out of ideas.
 24 September 2012 07:53 PM
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daveparry1

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Do you disagree with my last post then Spin?
Only trying to get you to see the regs. for what they are, "recomendations", obviously they should be complied with wherever possible /practicable but nothing statute about them.

Dave.
 24 September 2012 08:04 PM
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spinlondon

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Originally posted by: daveparry1
Do you disagree with my last post then Spin?
Only trying to get you to see the regs. for what they are, "recomendations", obviously they should be complied with wherever possible /practicable but nothing statute about them.

Dave.


Are you seriously asking me to comment on your inane post?
What bearing does your post have in a discussion about how to achieve compliance with the Regulations.
 24 September 2012 08:18 PM
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OMS

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Do we "comply" with the regulations, Spin

personally, I endeavour to meet the functional requirements of the regulations

Regards

OMS

-------------------------
Failure is always an option
 24 September 2012 08:21 PM
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davezawadi

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Spin, you have it wrong, and often do. The intention is all important, not the epistemological rubbish (I hope you understand that word, it is rarely seen here). The intention is quite clear, that a single failure should cause as little disruption as practicable (another long word), not as "is possible" given infinite resources. Whilst great fuss was made by manufacturers of the "17th edition board", this does not really solve any problems, just gives them a bit more money. Inconvenience really means that every installation needs an AMF (automatic mains failure start) generator system, just in case the DNO has a problem. As this is quite rare, except for hospitals and server farms, we should be more reasonable and accept that inconvenience is more than just no lights. It is very inconvenient if a fault sets the house on fire or you get a fatal shock using the lawnmower. 314 was never intended to be a reason to leave other potentially worse outcomes in place! If interleaved circuits, every other fitting on a different RCD etc were a requirement why do you think there are no regulations saying so? Simply that this should be reasonably interpreted as a need to do the design in a user aware way!

-------------------------
David
CEng etc, don't ask, its a result not a question!
 24 September 2012 09:15 PM
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weirdbeard

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Originally posted by: spinlondon

I'm begining to think, that perhaps I've stumbled onto the Screwfix forum rather than the IET's.

I can only assume from the last couple of pointless comments, that you guys have run out of ideas.


I take it you are unwilling to describe why you think my comment was inane?
 24 September 2012 09:38 PM
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ebee

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personally I said for years that the only way to comply with the reg to minimize inconvenience in case of a fault etc would be to put each point on it`s own RCBO (or MCB) which might be desirable but a little OTT for the vast majority of installations.

I don`t think "Minimize" is the correct word but then again "Reduce" wouldn`t fit the bill either.

I guess nonof us actually comply even though we strive to !

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
IET » Wiring and the regulations » To be an RCD brd or not to be!

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