Electrical concerns

On 09/09/2010 22:13, Tabby wrote:

When considering any wiring changes where the justification is "safety", one has to look at the overall picture. A blanket statement that "a new CU is a real waste of money" is potentially reckless IMO. Indeed there are many times where this will be true, but there are also some times where there is real value in a change of CU (or other electrical upgrade).
While deaths from electrocution are indeed very rare, death is not the only bad thing that can happen; shocks, burns, and house fires etc are also undesirable while also being more common outcomes of electrical accidents. Trips and falls (especially in the dark) even more so.
Things to consider when looking at risks are factors like:
Are there kids or old or infirm people living in the house?
Is there a garden or garage where electric power tools might get used?
Is there an excess of extension leads in use posing a trip hazard?
Is there poor discrimination - especially the 15th edition style "whole house" RCD or even older VO ELCB?
Is a lack of sockets resulting in dangerous overloading using old unfused adaptors?
Are leads being draped over hot surfaces due to poor positioning?
Are people likely to abuse rewireable fuses?
Is the lighting adequate and in the right places?
Are there mains powered interlinked smoke alarms?
There are also less obvious modern trends to look at, like upgrading thermal insulation in houses. It may mean that circuits need their current rating downgraded (especially if rewireable fuses are in use), and or need dividing into additional circuits. Replacements to service pipes in plastic may have knock on effects on earthing and bonding and also the correct functioning of protective devices.
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Cheers,

John.

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Around 20 deaths by electrocution & 400 or so by fire a year. RCDs or RCBOs could at best only stop a percentage of those. Even 10 on smoke alarms would stop more.
Compare that to a quarter of the entire population dying from easily preventable causes, 6 figures per year. Half the population dies from heart disease & cancer, and the general concensus is that half of those are easily preventable by improving diet & similar measures.
Its all about lives per pound and per hour spent. If you look at the top 10 killers and narrow it down to the easily preventable ones, it becomes clear that updating a fusebox in good working order is bordering on an exercise in denial.
NT
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On 10/09/2010 08:38, Tabby wrote:

Again you are looking at the problem in a very restrictive and narrow way.
Expand that out to include injuries and non fatal fires and you have a (significantly) larger number. Smoke alarms are indeed worthwhile, and to give you the best chance of working when needed really, need to be mains powered and interlinked. This alone may be potential reason for a change in electrical equipment (to provide an extra way on a CU etc).

I would argue that many of these are not "easily preventable" in practice, and certainly not with a one off personal investment of a couple of hundred quid. "Easily preventable were it not for human nature" might be a closer approximation.

If you are a government, looking at ways of best spending public money (or committing future public money with legislation change) then this is a valid analysis. If however your primary concern is not twisting you ankle every time you put the bin out at night, 100 spent on exterior lighting will very effectively solve that problem, whereas its unlikely its enough for one to single handedly find a cure for cancer.

Well much hinges on your definition of "fusebox in good working order" does it not? Taking a safe and working installation, and changing the fused CU for a modern one just for the sake of getting MCBs is indeed fairly pointless in itself. Although it might be worth doing if there was a sole occupant of the house, and they would be unable to rewire a fuse if it blew.
A significant number of people are injured doing silly stuff in the garden with mains leads. I would argue that 10 spent on the RCD plug, or 25 on a RCBO for the circuit is money well spent if it prevents a serious shock (and the potential complications arising from it). The cost of a single trip to A&E will vastly outweigh the cost.
Take a real case by way of example. When I moved into the current house there were a number of electrical problems that soon became apparent. The first was the oft encountered "whole house" RCD[1]. This was protecting far too many circuits and used to trip with some regularity (at least once a week). Now in simple cost terms alone (i.e. the time wasted resetting it, and resetting clocks etc) it was worth changing, never mind the annoyance. However its tripping highlighted other issues. Notably, that at night without electricity, its *very* dark here (no street lighting). The chances of everybody being able to get out in an emergency with no lighting were limited, and the prospect of injury high. There were no smoke alarms. There was very little outside lighting, meaning that a trip to the car or to put the bin out, would also often result in walking into things or tripping on something.
Personally I thought it very worthwhile spending a few hours and a few hundred quit correcting that lot (and a few other faults not mentioned). Not only are the prospects of escaping a fire now very much better, but general quality of life has been improved.
[1] TT install, so "no RCD" is not an option either
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Cheers,

John.

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On 10/09/2010 14:57, John Rumm wrote:

I presume that's a regulatory issue?
[I'm guessing that TT installs have been around for longer than RCDs - so that there must have been TT/non-RCD systems at one time.]
I rather suspect that the house where I grew up was like that. There was an overhead supply and an earth spike, but for lighting only - we didn't have any power sockets until I was much older and my parents acquired an electric fire. Prior to that, things like electric irons had 2-pin bayonet plugs on the end of the flex, and plugged into lighting sockets in place of the bulb.
For good measure, the electricity meter was directly over the (downstairs) bath - so you could have copped hold of it while standing in a (metal) bath of water.
I'm sure that all the latest regs are worthwhile - but it makes you wonder how so many of us survived without them in the past!
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Cheers,
Roger
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On 10/09/2010 19:45, Roger Mills wrote:

Well yes, but for technical reasons. Usually its hard to get a decent earth (i.e. one that can pass enough fault current to open a circuit breaker) with a spike alone. So a RCD solves that problem nicely.
On normally uses a much higher trip threshold device (typically 100 or 300 mA) for this application than one designed to protect from direct contact electric shock

Yup they used to use voltage operated Earth Leakage Circuit Breakers. These can work quite well if installed and tested correctly (most woere not!), but could fail to work in anger for a number of "external influence" reasons.

With lighting only its not so bad - an earth fault even with 10 ohms of spike resistance in it will still pop a 5A fuse. (possibly a moot point since contemporary lighting circuits probably did not have earthed lighting circuits!)

Nice ;-)

Partly by have far less access to electrical "things" to play with in general. Imagine what that house would be like with today's mess of AV kit, computers, phone chargers, vacuum cleaners etc hanging off it!
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Cheers,

John.

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On Fri, 10 Sep 2010 19:45:47 +0100, Roger Mills wrote:

And how a lot of the world survive with ad hoc (aka illegal) supplies and all manner of dubious wiring and connections. You know in some places they even wrap insulation tape around twisted together wires, what ever next!
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Cheers
Dave.




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