Earth funnies and phantom voltages on lighting circuit

[JohnW2]

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.

That's a bit like the corollary of the fact that we don't hear on the 6 o'clock news every night about all the planes that haven't crashed, all the people who haven't been murdered or raped, all the natural disasters that haven't happened etc. etc.!

You are aware of the 'numerous items' because you had been 'called out' because of them. To get even a feel as to what that means in terms of how 'probable' such events are, you would have to compare your experience with the countless (probably millions or much more) 'installation-days' in your area, during the period of your working career, when you had not been called out because of such a problem.

For the most part, they were simply due to a lost earth, with which this thread began, but not all.

A 'lost earth', per se, should not result in anything becoming live.

 

[Harry Bloomfield]

You are aware of the 'numerous items' because you had been 'called out' because of them. To get even a feel as to what that means in terms of how 'probable' such events are, you would have to compare your experience with the countless (probably millions or much more) 'installation-days' in your area, during the period of your working career, when you had not been called out because of such a problem.

You used the words, 'improbable' and 'rare'!

 

[Harry Bloomfield]

A 'lost earth', per se, should not result in anything becoming live.

No, normally they would notice the 'tingle', but all it takes is a L to E fault, on any part of the circuit where the earth has been lost, for it to be much more serious than a 'tingle'.

 

[JohnW2]

You used the words, 'improbable' and 'rare'!

I did, but what is your point?

Let's say that, over your entire working career, you had been called out, say, once every week to look at one installation because of "items which had for various reasons become live". If there were, say, 100,000 electrical installations within your area (which would probably represent a fairly small 'area), that would mean that, each week there will there had been about 100,000 other installations which could (but, in nearly all cases, won't) have experienced the same problem as the one you had observed.

OK, you obviously would not have seen anything like all of such incidents that had occurred in your area, so will have 'missed' some of the similar problems, but 1 vs. 100,000 suggests to me that the incidents you saw were pretty 'improbable'/'rare'.

 

[JohnW2]

No, normally they would notice the 'tingle', but all it takes is a L to E fault, on any part of the circuit where the earth has been lost, for it to be much more serious than a 'tingle'.

Indeed - but, as I observed, it is wrong to suggest that an item can 'become live' as the result of 'losing an earth'. It's only if there is also a 'fault to L' that it could become live.

 

[SUNRAY]

I've certainly experienced similar but working in the controls environment one tends to come across some out of the ordinary devices and in the water industry frequently piped with high pressure plastic pipe, a number of times I've come across a metal fitting in such a pipe which has been live, including things like flow meters with no direct electrical connexions or indeed no electrical connexions at all.
All too often it happens after pipework alterations where a decayed metal pipe is replaced with plastic and suddenly a faulty mains powered device is not earthed by the pipe. Additionally such a fault is usually found by other means

However I'd have to say not a frequent occurrance, maybe as many as a dozen times and one time was when I discovered some shower heaters used a non insulated heater element and it had gone open circuit.

edit: It was after one of those events that I tried the experiment

 

[JohnW2]

.... with high pressure plastic pipe, a number of times I've come across a metal fitting in such a pipe which has been live, including things like flow meters with no direct electrical connexions or indeed no electrical connexions at all.

Interesting. Are you implying that you believe that such items "with no electrical connections at all" come to be 'live' as a result of conduction through the water they contain? If so, I would remind you that I have acknowledged that a 'pipe-full of water' is a very different kettle of fish from a stream of water flow from a tap or shower head through air.

I fear that some people reading my recent exchanges with Harry may think that the two of us are 'miles apart' in our views, but I don't really think that is the case.

I think that both Harry and myself have the same conceptual belief - that in the face of certain events, it's 'safer' (less chance of serious electric shock) for touchable metal (e.g. pipes/radiators) to be earthed, but that in the face of other possible events, it is safer for that touchable metal not to be earthed. Which is, on balance, more likely (but not guaranteed) to be the 'safer' therefore depends upon one's view as to which of those two types of event is the more likely - and I think that differing views about that (which, in the absence of hard data, will always be personal opinions) is probably the only difference between Harry and myself.

It's a bit like discussions with bernard about the earthing (or not) of, say, otherwise 'floating'/unearthed metal baths (plastic piping and wastes). On one hand, something (e.g. frayed appliance cable touching it, or live appliance dropped into the water it contains!) could make the bath 'live', so that someone touching it and simultaneously touching something else which was earthed could suffer a serious shock. On the other hand, someone might touch something else which was 'live' (e.g. frayed cable of vacuum cleaner) and simultaneously touch an earthed bath, again risking a serious shock. In the former situation, earthing the bath is 'safer', but in the latter situation it would be 'safer' if the bath were not earthed. Bernard seems to believe that the former of those scenarios is more likely - so that, on balance, earthing the bath is the safer of the two options, but I don't think that I share that view about the relative likelihood of the two scenarios.

 

[SUNRAY]

Oh yes a pipe full of water, particularly in a closed system with it's 'additives and deposits' is very different to a water jet. Also I'm not implying all such faults are of a low enough impedance to be a serious hazard (at the same time I'm not trying to diminish the danger).
I don't think any of us are poles apart, just a question of personal experiences.

Perhaps the big risk is the powerfull vacuum cleaner in the loft plugged into the socket on the lighting circuit vibrating itself through the plasterboard and landing in the bath talking of which it has been quiet recently - no comment required.

 

[JohnW2]

Oh yes a pipe full of water, particularly in a closed system with it's 'additives and deposits' is very different to a water jet.

Indeed - as I've said, that's what I intuitively think.

Also I'm not implying all such faults are of a low enough impedance to be a serious hazard (at the same time I'm not trying to diminish the danger).

Nor am I, but I do suspect that, in the case of the 'waterjet' it's very unlikely to be a serious hazard. However, I'm far less comfortable about 'a pipe full of ('unclean') water. If I can trip and RCD with a 'wet rag, then I certainly would not want to trust my life to a 'pipe full of water'!

I don't think any of us are poles apart, just a question of personal experiences.

Indeed, that was my point. There is no 'right and wrong' to what we've been discussing, since the relative 'safety' of earthing vs. not earthing will always 'depend' (on the particular circumstances), so all we can do is to try to assess the relative likelihoods of different alternative scenarios - which, in the absence of data, will always be a matter of personal opinion/judgement, inevitably highly influenced by what we have 'happened' to experience ourselves.

Perhaps the big risk is the powerfull vacuum cleaner in the loft plugged into the socket on the lighting circuit vibrating itself through the plasterboard and landing in the bath talking of which it has been quiet recently - no comment required.

... or perhaps just the vacuum's hose falling through a hole in the plasterboard, dangling into the (full of water) bath below, and sucking up the water until it created an electrical path between the bath and the electrics of the vacuum