Terminating unused electric cable

[JohnW2]

By being non specific and it seems intentionally "vague" they are I guess opening the door for people to use common sense as well as the basic but vague requirements set out in the regulations.

Exactly - in essentially the same was a Part P does. However, in present context, as I said, that means that anything which (in terms of common sense) is not compliant with Part P will probably similarly be non-compliant with the 'common sense' general regulations in BS7671.

Kind Regards, John

 

[EFLImpudence]

but the basic effect of a failed Neutral and a sub 1 ohm path to ground resulted in a lot of damage to equipment as ground bonding over heated. On a domestic situation several fires have been started by over heating bond wires ( mostly where the CCC of the bond was too small ).

Was the PFC not noted?

 

[ban-all-sheds]

Bernard - are you claiming that BS 7671 is not even reasonably safe, and that it would be unreasonable for people to work to it?

 

[bernardgreen]

Bernard - are you claiming that BS 7671 is not even reasonably safe, and that it would be unreasonable for people to work to it?

NO I AM NOT and it amazes me that even you could come to that interpretation of what I said. Compliance with BS 7671 will result in 99.9 % ( or there abouts ) of installations being safe and reliable. But also in maybe 0.1 % ( or there abouts ) of installations circumstance not foreseen by the writers of BS 7671 will require a deviation from BS 7671 to be 100 % safe.

 

[ban-all-sheds]

So you don't think that being safe "99.9%" of the time qualifies as reasonably safe?

 

[bernardgreen]

So you don't think that being safe "99.9%" of the time qualifies as reasonably safe?

Not 99.9% of time, 99.9% of installations.

 

[ban-all-sheds]

Same thing. "99.9% of the time" ≡ "99.9% of instances".

So you don't think that if 99.9% of electrical installation work done in accordance with BS 7671 is safe that makes BS 7671 a reasonably safe standard to work to?

 

[JohnD]

Does 99.9% of the time mean that for one day every two and a half years (approx) it becomes unsafe? That's not good enough.

99.9% of instances might mean that 1 person in a thousand is killed by an electrical fault. That's not good enough.

 

[ban-all-sheds]

Or it becomes unsafe for 86.4 seconds per day. That would be OK if we know which 86.4s it is.



[EDIT]Stupid arithmetic error corrected.[/EDIT]

 

[bernardgreen]

If 99.9 % of installations are safe then 1 in every 1000 will be always be unsafe

If during 99.9 % of time installations are unsafe then every installation will be unsafe for

a. 8.64 seconds per day
OR
b. one day every two and a half years (approx)
OR
c. a number of periods of time that amount in total to 0.1 % of the elapsed time since the electrics were installed.

 

[JohnW2]

If 99.9 % of installations are safe then 1 in every 1000 will be always be unsafe ........

Yes, but that's only the start of it, depending on what one means by 'unsafe', and the nature of the 'unsafeness'.

If one uses the most 'natural' meaning of 'unsafe' (e.g. unearthed metal light fittings, inadequate CSA of bonding conductors, theoretically 'slightly inadequate' CSA of other cables etc. etc.) than it is quite possible that the probability of that "unsafeness" (when present) 'never' (or never within a specified time period) resulting in harm to persons or property is also of the order of 99.9%. If that were the case, then the probability of harm to persons or property (ever, or within a specified time period) would be of the order of 1 in 1,000,000.

To put that into context, you (and I) have about a 1 in 2,700 chance of being killed or seriously injured on the UK roads in the next 12 months (killed about 1 in 37,000; seriously injured about 1 in 3,000)

Kind Regards, John

 

[ban-all-sheds]

To put that into context, you (and I) have about a 1 in 2,700 chance of being killed or seriously injured on the UK roads in the next 12 months (killed about 1 in 37,000; seriously injured about 1 in 3,000)

You cannot in any meaningful way say what your, my, or Bernard's chances are of that. We all use different roads, types of roads, in different ways, at different times, and for different amounts of time. Population outcomes cannot be used to infer individual ones. I think it was a Tommy Cooper joke which went something along the lines of

A man gets knocked over by a car every hour in London.

He's getting pretty fed up with it.​

There is a serious point - we might consider that a 1 in 2,700 chance of being killed or seriously injured on the UK roads in the next 12 months meant that the roads were reasonably safe, but if we found out that a child walking to school had a 1 in 100 chance of being killed or seriously injured in the next 12 months we might not.

So Bernard's assertion needs the same scrutiny (whatever the % figure he wants to use). If we knew that some bizarre influence made our electrical installation unsafe for 86.4 seconds per day we'd probably not look on that in the same way if it were 3.6s every hour or a block of 8.76 days every year.

 

[bernardgreen]

BAS If an installation is safe when installed then it remains safe until altered either intentionally or by accident. It does not become unsafe for a while and then revert to being safe again unless it is altered or damaged and then restored or repaired to be a safe installation.

 

[ban-all-sheds]

OK, so a hypothetical external influence which made all installations unsafe for a period of 86.4 seconds a day would not, in your eyes, result in that figure of "99.9%".

TBH, I never, not even for 0.1% of the time, thought that was what you meant, and it seems such an unlikely scenario for anyone to imagine that I cannot begin to think of a reason (which would not be removed by the Mods) for you to act as if that was what I meant when I wrote "So you don't think that being safe "99.9%" of the time qualifies as reasonably safe?".

So can we now return to the plot?

Do you think that if 99.9% (or thereabouts) of installations done in compliance with BS 7671 are "safe" then working to BS 7671 is a reasonably safe thing to do?

 

[stillp]

BAS If an installation is safe when installed then it remains safe until altered either intentionally or by accident. It does not become unsafe for a while and then revert to being safe again unless it is altered or damaged and then restored or repaired to be a safe installation.

Depends how you judge "safe" Bernard. The degree of risk in any installation will depend on how it is used or misused, external influences such as lightning strikes, whether persons are present or not, etc.