NT wrote:
On Jul 23, 8:23 pm, John Rumm wrote:
NT wrote:
I think there are two things at issue he
One is semantics - yes you could argue that if you are changing nothing,
then installing bonding is not "required".
Thats a true fact, not semantics 
Not really - the wiring regs still say its required. The fact that there
is no legal compulsion to update the exiting install to follow those
requirements does not make the requirement go away.
it means that, by definition, it isn't required for most houses.
There is simply no requirement for most houses to be to current
standards, and the great majority aren't.
We can go round in circles on this. Yes I agree there is no legal
requirement to bring an old install up to current standards. Unless you
change anything. However that just means that it is allowed to to be non
compliant with the technical spec. The spec's requirement's however have
not changed.
By all means tell em that they are not legally obliged to carry out the
work; but if the PIR has highlighted a fault that should be fixed,
unless they are in a position to carry out enough analysis to say if
there is a better cost benefit trade off to be had elsewhere, they ought
to carry out the fix.
There is simply no basis for saying the missing bonding should be
fixed. The cost/benefit analysis shows it to be at best worthless, and
Your cost benefit analysis is looking at it from the wrong perspective.
I agree that there would be no point in legislating that all properties
must be inspected and have it added if required and missing. The cost
would be disproportionate to the benefit.
However that is a very different argument from the case where you have
been informed by a professional that the installation is at fault and
you need to asses the significance of that fault.
the legal position is that it is not required in most cases.
If you are doing nothing to an installation, then you are not obliged to
upgrade it to meet the requirements.
Any other advice would be reckless.
Telling the truth about the legal position is not reckless or unwise.
We are not talking about the legal requirements. We are talking about
giving good advice, and doing a proper job. We have already stated the
legal position. By all means add further words if you think it would help.
A couple of example scenarios:
e.g.
1) 16th edition PMR head end, small shower room, plastic pipes
everywhere and the only electrical circuits in use are the lighting one,
and a spur from a upstairs ring circuit to feed a towel rail. The lights
are SELV downlighters. The actual risk of serious shock in this
circumstance is negligible. Since mains never manifests in the room
anywhere other than the towel rail, and there are no other extraneous
conductive paths (the CPC of the lighting circuit does not present in
the room - the metalwork of the down lighters is floating, the switch is
non conductive and out of reach on a string). According to to the Regs
Bonding is still required, however the implications of ignoring the
requirement are to all intents nil as things stand.
2) 15th edition install, re-wireable fuses, TT head end (overhead wire
supply), no bonding at all (main or supplementary), a VO ELCB is
connected inline with the main earth provided by a gas pipe. There are a
number of borrowed neutrals and neutral earth faults. a 13A socket is
installed beside the sink to allow a hairdrier etc be plugged in.
Bathroom has CH piped towel radiator, metal pipes to all taps and
cistern, and an electric shower, plus fan heater, and some class 1
luminaries on a low ish ceiling controlled by a nice polished chrome
wall switch next to the shower. In this case there are any number of
fault scenarios that could present serious and life threatening shock
hazards i.e. faults that could leave high touch voltages on metal
surfaces for extended periods, with ready access to an independent earth
close to hand. Now obviously a PIR would highlight all manner of
shortcomings here. The long term solution would probably be a package of
measures including a re-wire or at least a new head end. However
installing main and supplementary bonding PDQ would be cheap and
effective way to lower the rooms status from "death trap" to something
more acceptable.
You're missing the point I made last time. You may /imagine/ some
unbonded bathrooms to be deathtraps, but the figures (ie facts) show
very clearly that they're not.
Again you are attempting to carry out an epidemiological study (without
access to the raw data I might add). We are dealing with rare events and
small sample sets. We may hear about the deaths, we probably don't hear
about the vast majority of injuries and shocks.
It remains the case that EQ bonding in a bathroom is a cheap and easy
fail safe measure that may well be conclusive in the event of another
failure.
it seems evident that cost/benefit is relevant, and is in fact
precisely the grounds on which we make decisions as to what to spend
on safety.
Lets take an example: imagine you have 2 options, to spend £60 on
getting the car's brakes fixed or to spend on equi bonding. You know
that there are around 3500 deaths per annum from car crashes, and
around 0.2 from bathroom electrocutions. In each case spending the £60
would decrease those risks, but not to zero. Its obvious what one
would choose, the question is how? If you don't think its on cost/
benefit ratio, on what basis do you make the choice?
You don't provide enough information to make the choice. If your
particular bathroom happened to be like the one that Andy W posted a
link about, then the liklihood that you are going to fall into your 0.2%
is very nearly 100%. Its a pretty good certainly that someone would get
a serious shock before long.
If money is so tight, then why pay the £200 - £400 for a PIR if you are
not going to be in a position to fix any faults it finds? You would be
better of fixing the car and spending some time reading about what
constitutes a safe electrical system.
throw up reams of faults that he does not
understand; missing bonding being one of them.
If there are reams of faults, a rewire would be a lot more sensible
than fitting equi. And if Joe were too broke to do that, spending the
money on fixing some faults would be far more worthwhile than fitting
equi. And once all the faults are fixed, then adding equi becomes
valueless anyway in safety terms.
I don't agree. EQ bonding is a fail safe technology. Fixing current
faults is no protection against those that may occur in the future.
Bonding is.
The only sensible advice
we can give in a general purpose guidance article is to say you need to
be lead by the professional opinion of the people you have paid for
advice
I don't see any reason for us to even comment on that.
Re equi bonding, why not just state the truth, that its required when
doing electrical work?
We have said you are not legally obliged to upgrade. That is closer to
the truth I would say.
Most informed people asked to say where the *requirements* for
electrical installations are specified, would say BS7671. According to
that, bonding is required (17th edtn spec installs excepted).
and here is what the bonding does and how it works if you want to
know. The implications of it not being there may be trivial, or may be
very serious, we can't tell you from here.
yes we can, we know ballpark figures on this.
Without detailed knowledge of the installation in question you don't,
you only have stats which by definition are not specific.
(Note also this is partly a circular argument. We have very safe
electrics in the UK as a general rule - both fixed, and appliances (the
former more so than the latter). Deaths are very rare, and injury
relatively rare. Part of the reason for this is that we do specify and
install safety measures like EQ bonding, RCD protection and a host of
other measures.
the majority of domestic installs in the UK predate equipotential
bonding, and a large percentage still have no RCD. The national death
Do you have a source for this claim? EQ bonding goes back to at least
the 14th edition - so that is 1966. I would be very surprised is pre
WWII wiring installs were still in the majority.
rates from electrocution apply to all systems, risks added up, not
specifically to newer one with rcd/equi.
Why not...
Lets say install cost £20 materials, 4 hours labour for a diying
novice, including going and getting the bits.
Total cost £20 + 4x7-15, perhaps £40 as a balpark figure
= £60 total
So the question that matters to me is, could that £60 save the life of
someone in the family should something go wrong? The answer is usually yes.
The answer is fairly clear: Yes in approx 1 per 5x 20 milion
households = 1 in 100 million odds of it being of any use in each
year.
useless analysis - we are not talking generalisations. I want to know
what it means for *my* installation.
So the next question is, how likely is it that something will go wrong
in a dangerous way, with my particular installation, that means I would
get to "use" that £60s worth of investment and hence make it worth
spending here and not on mitigating some other risk. If the answer is
"high to moderate" then you spend the £60. If the answer is "I don't
know" the next question is can I get sufficient expert analysis at less
cost, that would tell me if its going to make a difference. If the
answer is no, then you spend the £60. If the answer is yes then you
spend the money on that instead, and then possibly spend the £60
afterwards as well depending on the outcome.
we know the answer is around one time per 20 milion households per
year. 1 per 100 million.
we don;t actually - even in general terms. There could be hundreds of
people who are alive, well and uninjured or hurt that are possibly even
unaware that they were saved by a protective system such as those being
discussed.
results given are sometimes entirely unrealistic and to encourage
needless spending.
Agreed; and sometimes the results will be highly realistic, and
encourage spending on something that needs doing as a matter of urgency.
How do you differentiate without detailed technical knowledge?
national death statistics. Then one calculates approx cost/benefit for
safety measures.
No, I can't see the logic here.
Depending on the *actual circumstances* the chance that a protective
measure will have a decisive effect on the outcome will vary in
probability from nil to 100%. Personally, if the risk in my house is
nearing 100% I am not going to draw any comfort from the fact that
according to national statistics I died in a very improbable way.
Perhaps there is a whole new article there; "My PIR said X, how much
notice should I take?".
or 'what does this mean in real terms?'
yup. However to do any good, it is going to have to impart sufficient
technical know how to make a decision based on the facts of the actual
installation, and not just state heuristics based on statistical
likelihoods.
[1] although following the logic, part P would never have been
introduced - which shows up the disparity between stated and real agenda.
Spending money on safety measures that yield little only leaves less
money to spend on safety measures that are of genuine importance.
yup, I agree.
In this case the cost/benefit ratio is 1/ 6billion to 1/ 30k = a ratio
of 200,000:1. IOW spending that £60 per person on useful measures
could save 200,000 as many lives as by spending it on equi bonding. So
realistically, its fatal in many cases.
woosh...
Given this, why claim its always required when it isn't?
How about because the requirements say so?
Or if you think it is required for all houses to meet latest wiring
regs, which act of law do you believe says so?
I believe one is not legally obliged to upgrade to meet the current
requirements. If you want the requirements they are available from
Amazon et al.
--
Cheers,
John.
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