Again, I will have to disagree with you. The difference between making contact with a dry live cable (or similar live part), and water that is live, is the much greater area of contact, plus likely volume of water.
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Earth funnies and phantom voltages on lighting circuit
- Thread starter thesled
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Again, I will have to disagree with you. The difference between making contact with a dry live cable (or similar live part), and water that is live, is the much greater area of contact, plus likely volume of water.
If most of the pipework were electrically isolated from electrical things (CH pumps/valves/boilers, immersions, showers etc.) how do you envisage that the pipework would 'become live'?
There's nothing wrong with our disagreeing!
However, one of the main issues about the theoretical conduction of electricity through water in this situation is that it is based on the assumption that there is a 'solid block of water' from where there is some 'live electricity' to where it is in contact with a person. In practice, what hits the person is likely to be a shower of 'droplets', not in close contact with one another - which is one of the reasons why the conductivity of 'a tube full of water' is much greater (albeit low, for 'clean' water) than the conductivity of water 'flowing' out of a tap or shower head.
I have to say that I am a bit confused by this worrying about the conductivity of the water in the pipes.
Need anything be done to safeguard against it?
I have never considered it apart from the very small distance a joint may separate two metal parts.
If the conductivity of the water were anything to worry about then surely the water itself would be acting as a bonding conductor joining the originally bonded pipe to the now isolated (apart from the water) pipe.
So - do we, in fact, need to bond any water pipes? They all contain a conductor wherever they go.
Do they still make metal hoses for showers? They could be a worry.
Need anything be done to safeguard against it?
I have never considered it apart from the very small distance a joint may separate two metal parts.
Regarding the emboldened sentence.
If the conductivity of the water were anything to worry about then surely the water itself would be acting as a bonding conductor joining the originally bonded pipe to the now isolated (apart from the water) pipe.
So - do we, in fact, need to bond any water pipes? They all contain a conductor wherever they go.
Why is that bad? Would it not cause the protective device to disconnect the supply.
Do they still make metal hoses for showers? They could be a worry.
As I wrote, I've never really thought of it as something that one needs to 'worry about' - not the least because of what I say about the 'stream' of water (droplets) from a tap or shower head being very different from a 'solid block' of water in a pipe.
Quite. I do not believe that the contained water would be anything like conductive enough to be usable as 'bonding'.
I think that many/most of them are still 'metal', at least on the outside, but it's possible that, in many cases, that metal surrounds a non-conductive tube/pipe within. However, even if it is all metal, I think that the hose is almost invariably screwed on to a plastic connector - so, again, any electrical 'continuity' would have to be due to the water.
Metal pipework, expanding and contracting, rubbing against live cables. Nails and screws, piercing cables, and contacting pipes. Fixing screws for radiator brackets, making contact with buried cables in walls. There are lots of ways for metal to become live.
The flow does usually break-up, but not close to the shower head, besides, and people do reach up to adjust the position of the head.
That, would depend upon the relative resistances of the two paths - from shower head, through the body to ground, versus the alternative. If the alternative, is through the shower, fed via plastic pipe, and the rest of the pipes are plastic, the 'water column' resistance, could be much higher, than via the body.
The normal for electric showers, is a plastic 'liner' pipe, spiral wound with a metal - rather like the old flexible conduit.
There are, although I would personally think that all the things you mention are extremely improbable (very rare) - and, importantly, probably more improbable than 'other things' becoming live (or indeed, silly people touching intentionally live things) - in which latter case the risk of shock is slightly increased by having earthed pipework/radiators etc. around that could be touched simultaneously.
That's all theoretically true.
As I may well have reported here in the past, a long time ago, in response to discussions like this one, I did an experiment in which I had water coming out of a (metal) tap and 'pouring onto' a copper 'electrode' at various distances from the tap - and the resistance between tap and electrode was always much higher than would give me any 'cause for concern'.
Much depends on the purity of the water, experiments we did some decade plus ago we were able to trip a RCD at a bit under a foot but repeating with exactly the same kit some 100 miles distant it was almost unrepeatable.
The conductivity of the mains water supply, varies quite dramatically from area to area, but it's not something the water companies usually specify.
Indeed, the purity of the water has a very marked effect on conductivity. However, one would expect hard water to have higher conductivity than soft, and I've only ever lived in very hard water areas, so the experiments I've done in the past must have been in that context.
In experiments, I've certainly got RCDs to trip by dropping a 'wet cloth' onto a pair of conductors, one connected to L and the other to E - but, again, there is then a fairly 'solid mass of water' between the two electrodes, which is rather different from 'streams of water' flowing in air.
During my working career, I was called out to numerous items which had for various reasons become live, so I would not call it either improbable, or particularly rare. For the most part, they were simply due to a lost earth, with which this thread began, but not all.
Mine (Anglian Water) certainly does, along with countless other chemical and physical properties of the water in their reports, and I'd be surprised if yours did not do the same ....
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