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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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 08 October 2012 01:15 PM
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spinlondon

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Originally posted by: AJJewsbury
Andy do agree that however reasonable your actions may be, they would result in an impairment of safety?


I prefer the interpretation: If the results still comply with BS 7671, then it's deemed to be "safe" - if it's "safe" then its safety isn't impaired.

Like I said at the beginning, the simplistic interpretation of the words out of context rapidly leads to such absurdity that it doesn't seem plausible that that was the authors' intention.

- Andy.


Andy the two requirements of 610.4 are to verify that the addition or alteration compies with BS7671, and that the safety of the existing installation is not impaired.
If compliance with BS7671 automatically ensures safety, then why the second requirement?
I don't agree that taking the words at their face value, is an interpretation, simplistic or otherwise.
How exactly are they being taken out of context?
 08 October 2012 01:35 PM
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AJJewsbury

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Andy the two requirements of 610.4 are to verify that the addition or alteration compies with BS7671, and that the safety of the existing installation is not impaired.
If compliance with BS7671 automatically ensures safety, then why the second requirement?

Like you sort of suggested earlier, I think the (intended) logic is the same as building regulations - i.e. new work is to:
a) itself comply with current standards (first requirement)
b) anything existing which doesn't comply with current regs is made 'no worse' than it was before (second requirement).

How exactly are they being taken out of context?

1. by ignoring reg 120.1 (the regs provide for safety - therefore an installation complying with the regs is deemed to be safe).
2. by not checking the reasonableness of the interpretation by considering the obvious consequences. (Surely not even the wiring regs committee would be that daft?)

- Andy.
 08 October 2012 01:53 PM
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OMS

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2. by not checking the reasonableness of the interpretation by considering the obvious consequences. (Surely not even the wiring regs committee would be that daft?)


Nice surroundings, warm room, good company, wine with lunch - anything could happen Andy

Regards

OMS

-------------------------
Failure is always an option
 08 October 2012 02:03 PM
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spinlondon

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Why is it that whenever someone disagrees with the wording of the Regulations, they always refer to 'the intent of the Regulations'?
Why can't it simply be the case, that a Regulation means exactly what it states?
We know that you disagree with this particular Regulation.
Your argument that you belive the intention is diferent from what is actually stated, is nothing more than a re-iteration of your belief.

I'm sorry, but the first requirement of the Regulation is to verify compliance with BS7671. Ignoring any Regulation would be a non-compliance.
Again you want to interpret words so that they mean something other than what they say.

Your whole argumant seems to based on interpreting words so that they mean something other than what they say and on some form of divination of the true intent of the people when they formulated the Regulation.

With such logic, why bother complying with any requirement?
 08 October 2012 02:29 PM
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AJJewsbury

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Why is it that whenever someone disagrees with the wording of the Regulations, they always refer to 'the intent of the Regulations'?

Probably because English isn't a perfect language, individual human thinking is fallible, amendments by committee if anything more so. And we do have examples of exactly that (RCDs for SELV circuits for example). Did you never come across errors in text books at school?

Why can't it simply be the case, that a Regulation means exactly what it states?

even if it's clearly absurd?

Nice surroundings, warm room, good company, wine with lunch - anything could happen Andy



- Andy.
 08 October 2012 03:39 PM
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spinlondon

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Why is it absurd?
It seems to me to be a perfectly reasonable requirement.
Consider for instance those installations where the requirements for safety exceed those set out in BS7671.
Such installations that may be covered by Local Authority Licencing, and those covered by Compex and Atex etc.
Or even juust a simple case of the designer decided that this is what should be.
I've worked on installations where every socket-outlet is 110V, fed from isolation transformers.
I could as an alteration or addition install 230V socket-outlets without 30mA RCD protection and comply with BS7671.
However the original design is that only 110V isolated socket-outlets be provided.
As such by installing the 230V socket-outlets, I would to my mind be impairing the safety of the installation.
 08 October 2012 04:01 PM
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AJJewsbury

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Why is it absurd?

Imagine the situation where you're asked to extend an existing installation.

You're almost certain to make some aspect fractionally less safe (in absolute terms) than it was before (higher Zs, lower insulation resistance, longer disconnection times, higher touch voltages, higher conductor temperatures), so even with the proposed addition completely complying with BS 7671 you say we should refuse.

So how does the customer get what they want? If they demolished the building, build an identical new one, obtained a fresh DNO supply and asked you to wire it from scratch, you could then do what they wanted as there'd be no existing installation to make less safe. I call that absurd!

I'm certainly not advocating ignoring any licensing requirement (or indeed customer requirement) - if they're still applicable. That would make the installation unsuitable for its requirements (and a contravention of 115.1 etc). But that's a matter of referring to and/or updating the requirements and design, not something that should necessarily be embodied forever in the physics of the existing installation.

- Andy.
 08 October 2012 04:05 PM
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ebee

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The safest thing (Electrically) would be to have no points in any location.
Our regs make having some points relatively safe.
If we have a room with no sockets in it is "safe".
If we put sockets in it becomes (very slightly) unsafe or less safe.

If a designer decides each room of a house has three twin sockets and we start adding more then we inevitably make it less safe than it already was. Even if the additions all comply with the latest regs.

The strict application of making it no less safe would prevent all additions

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

Knotted cables cause Lumpy Lektrik
 08 October 2012 05:58 PM
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spinlondon

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I believe Andy that I've already addressed those arguments in an earlier post.
However:
If you were to make an alteration or addition that caused such an increas in disconnection time, that BS7671 or the design specifications could no longer be met, then yes there would be an impairment in safety.
However a slight increase that did not mean such, would be offset by the slightly lower voltage and current.
As for a decreas in the measured value for IR, as long as basic protection is provided, or the value is suitable for the environment, I do not see that it would be an impairment.

Ebee, if you were to add extra sockets, willy nilly, then yes it could well be an impairment.
However if the extra sockets were added so as to inprove the user friendliness of the installation, then no. The extra risk would be offset by the improvements offered by providing sufficient outlets, by allowing shorter leads, by not having trailing leads providing a trip hazard, etc.
 08 October 2012 06:06 PM
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ebee

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OK then.
If I make additions that are not of benefit I break the regs?

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

Knotted cables cause Lumpy Lektrik
 08 October 2012 06:26 PM
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spinlondon

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Originally posted by: ebee
OK then.
If I make additions that are not of benefit I break the regs?


Sounds like a con.
Oh yes missus, you need 12 extra sockets, otherwise you'll be breaking the Regs.
I guess you could bond the crittle windows at the same time.

Edited: 08 October 2012 at 06:45 PM by spinlondon
 09 October 2012 09:55 AM
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AJJewsbury

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I believe Andy that I've already addressed those arguments in an earlier post.

You naysayed them, but without providing a convincing explanation.

If you were to make an alteration or addition that caused such an increas in disconnection time, that BS7671 or the design specifications could no longer be met, then yes there would be an impairment in safety.
However a slight increase that did not mean such, would be offset by the slightly lower voltage and current.

What lower voltage? R1/R2 acts as a potential divider - it's the ratio of R1:R2 that dictates the voltage at the fault, not their absolute values. Indeed, if you used reduced c.s.a. c.p.c.s then longer length (compared with Ze) would probably increase the touch voltage. Lower current means longer disconnection times. I'm not seeing any mitigating factors so far.

The extra risk would be offset by the improvements offered by providing sufficient outlets, by allowing shorter leads, by not having trailing leads providing a trip hazard, etc.

But how can that be shown without quantifying it? What's the risk and probability of each case?

- Andy.
 11 October 2012 08:00 PM
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weirdbeard

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Originally posted by: AJJewsbury

I believe Andy that I've already addressed those arguments in an earlier post.


You naysayed them, but without providing a convincing explanation.





This does seem to be the spinsters favoured modus operandi!
IET » Wiring and the regulations » To be an RCD brd or not to be!

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