Playing devil's advocate, what about the case of a shower with the water running? There could be a continuous stream down to the drains underground and thus earth. Or for a bath you could touch earthy taps. Or holding a shower head with a metal outer that connects back to the water pipe. I don't see that it at all a safe assumption that the body is isolated.
Gas pipe bond (IET vs Corgi)
- Thread starter Malc
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It sounds as if you may be related to bernard! People often come up with that one, but I've never heard of anyone actually coming to any harm (or even experiencing a shock) as a result of electricity being conducted through a flowing stream of water.
Even a 'continuous static column' of of tap water (e.g. in a vertical plastic hose, with a cork in the bottom!) without any 'gaps' or 'air bubbles' will have a pretty high impedance.
In any event, what are you suggesting can be done about it? If any hazard exists, it exists because there is some degree of electrical path to earth through the water, and one cannot do anything to get rid of that.
Same question as above - if the taps, shower head or whatever, are connected to earth, then they are connected to earth - and that does, indeed, introduce a potential hazard if someone somehow manages to touch them at the same time as touching something 'live' (obviously extremely unlikely), then what are you suggesting can be done to reduce that risk?
Of course, if the taps (or whatever) are not connected to earth (e.g. because of plastic piping), then someone who unnecessarily 'bonds' them to earth will actually be creating the very hazard to which I have referred.
Kind Regards, John
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I'm not sure what is 'mini' about it, but as the title of that says, it is a "(Mini)Myth".
Kind Regards, John
I think that refers to the length of the clip - a shortened version of the original.
Ah, right - so it remains a (non-mini) myth
Many moons ago, I did try measuring the resistance between water in a plastic beer keg and a metal plate onto which water was pouring out from the tap at the bottom of the keg - and, if I recall correctly, failed to measure any conductance (i.e. sub-infinte resistance) at all - certainly no degree of conductance of any significance.
Kind Regards, John
There are 2 assumptions that can be made. Body is insulated or body has good connection to earth. Worst case of those two is good connection to earth since if the body was insulated we could handle lives wires with no problem. So with that assumption, for safety, any other metalwork should be obviously isolated or failing that bonded to the same potential as the body. That would be my guess at the reasoning behind treating bathrooms as special cases. Otherwise, if you take water as immaterial and the body as insulated why treat bathrooms as special?
BTW when you tried to measure resistance in a flow of water what did you use? For liquids (and gases) the voltage will be important. Water needs a couple of volts to get the current flowing. But if the water is falling then it will likely split into droplets so have air gaps and thus no continuous path.
BTW when you tried to measure resistance in a flow of water what did you use? For liquids (and gases) the voltage will be important. Water needs a couple of volts to get the current flowing. But if the water is falling then it will likely split into droplets so have air gaps and thus no continuous path.
And what was in the water. Distilled ( pure ) water not a good conductor. But add some metallic salts and oxides and it can become very conductive.
The water circulating around central heating radiators has a lot of salts and oxides.
And why does pouring water around a ground electrode reduce the impedance of the electrode. Often the improvement takes some time to appear, possibly due to the water having to dissolve some of the salts etc in the ground before it becomes conductive enough to reduce the impedance.
It's a bit more complicated than that, in as much as the body may be connected (or not connected) to different things at different times - but, yes, in any environment (not just bathrooms) the risk of electric shock can obviously be eliminated by ensuring that everything touchable is at the same potential.
However, as I've said, I think a degree of common sense is required in deciding what "realistic" risks there are of metal objects (pipes or whatever) becoming 'live'. As I've said, the (incredibly small) risk of that happening is probably as great (maybe even greater!) in the case of a screw holding up a bathroom shelf or (maybe metal) cabinet as it is with a water pipe.
Good question - and, as with some other regulations/requirements, it might well have been a 'knee jerk' ("electricity and water don't mix") based on theoretical considerations, without any real evidence that electric shocks were any more common and/or any more serious in bathrooms than anywhere else.
I suppose that the most obvious reason for singling out bathrooms is that it is a place where people are frequently naked, with no footwear and with very wet skin (hence low body resistance). Hence, if there were (for whatever reason) any dangerous potential differences around, the risk of any resultant electric shock being 'serious' (perhaps fatal) is greater than in most other environments. Don't forget that until quite recently kitchens were lumped together with bathrooms as 'special locations'. However, that was dropped, quite probably because they realised that the (usual!!) absence of wet naked bodies in kitchens meant that they did not justify/require any 'special treatment'
It was a good few years ago, so I can't recall the details. However, I wouldn't have used a very low voltage, for the reason you mention. I almost certainly would have used an IR meter, in which case the testing would probably have been at 250V, 500V or 1000V (probably all three). If/when I have a few spare moments, I'll try a few more experiments!
That was, of course, my very point. In fact, because of cavitation, air bubbles etc., even water flowing within a pipe can be far less of a 'continuous tube of water' than you might think.
Kind Regards, John
It would have been tap water, and since I've always lived in very hard water areas, there would have been a good few salts in it.
That's a very good question which I have often pondered - and I can but presume that the answer is pretty complicated. Under protracted very dry conditions, the resistance of my TT electrode can rise to 80-90Ω but if I 'water it', the resistance then returns to its usual 40-70Ω (as you say, after some delay). I can but presume that it is to do with improvement of the connection between connection between the electrode and immediately surrounding soil (which maybe develops 'air pockets' when the soil is very dry and cracking etc.), since a modest amount of local watering clearly cannot have much impact on the resistance between the electrode and 'the body of the earth' if (as will be the case) all the surrounding soil is equally dry.
Kind Regards, John
But, getting back to point as we are drifting off topic, I reckon this:
In order to be seen to comply with the regs I reckon that I should take a bond wire to the gas meter box so the bond can be seen and inspected. I think I'll also bond at what I think is the "correct" place, in the floor void, just in case the gas meter box bond is ever removed. In effect I'll treat the external gas box as part of the house volume.
Bathroom Radiators with metal pipes disappearing beneath the floor or walls I will bond but not in an accessible place unless convenient. The logic behind this is that I don't have to bond these is the copper pipe work goes all the way back to the boiler so my bond is just replacing the copper pipe. A periodic inspection would either not care about the radiator or would seek to prove it had a path back to the boiler bonding. That would be done with a meter and not inspecting all the copper pipe so this is no different.
I suppose a solution to the inspection issue would be to solder the bond wire to the pipe clamp. The clamp itself has a lock nut so should not come undone due to vibration. Or maybe a just a lock nut on the back of the wire screw would do? It strange they don't make a "maintenance free" pipe clamp.
In order to be seen to comply with the regs I reckon that I should take a bond wire to the gas meter box so the bond can be seen and inspected. I think I'll also bond at what I think is the "correct" place, in the floor void, just in case the gas meter box bond is ever removed. In effect I'll treat the external gas box as part of the house volume.
Bathroom Radiators with metal pipes disappearing beneath the floor or walls I will bond but not in an accessible place unless convenient. The logic behind this is that I don't have to bond these is the copper pipe work goes all the way back to the boiler so my bond is just replacing the copper pipe. A periodic inspection would either not care about the radiator or would seek to prove it had a path back to the boiler bonding. That would be done with a meter and not inspecting all the copper pipe so this is no different.
I suppose a solution to the inspection issue would be to solder the bond wire to the pipe clamp. The clamp itself has a lock nut so should not come undone due to vibration. Or maybe a just a lock nut on the back of the wire screw would do? It strange they don't make a "maintenance free" pipe clamp.
You are confusing the two separate definitions of special location.
One is the Building Regulation, which used to include kitchens for notifiable work and did not relate to the presence of water.
The other is that of chapter 7 of BS7671 which relates to the presence of water and does not include kitchens.
In terms of electrical common sense, that's obviously fine. You might also just about be able to argue that it is reg-compliant - the regulation says that "Where practicable, the connection shall be made .... at the point of entry to the building if the meter is external". Crucially, it does not say whether that 'point of entry' is the external or internal end of the hole through the wall, so you could certainly argue that you were compliant by bonding outside, close to where the pipe entered the wall!
'Bond' to what? If your concern is about the regulations, don't forget that it is very probable that there will not be a requirement for any supplementary bonding in the bathroom.
Even if there were a requirement for supplementary bonding (unlikley), it would only apply to "extraneous-conductive parts" (not to 'all pipewok' or 'all metal'), and if that pipework could be shown (by testing) to be effectively connected (via pipework and boiler etc.) to the installation's earthing system, then it would not count as an extraneous-c-p and therefore would not require siupplementary bonding.
I personally wouldn't bother with any of that, and I'm not even sure that it would satisfy the worst of "Jobsworths" - they might argue that the connection between clamp and pipe needed to be 'inspectable' (for corrosion, if not 'loosening'!).
I think that they sort-of do. I believe that DNOs use 'sprung' (rather than 'screwed') clamps onto their cable sheaths for TN-S earths. However, I'm not sure how available they are, and have never heard of one being used for a bonding connection!
Kind Regards, John
As long as it has the desired result - and is inspectable - it doesn't matter where you bond it.
At point of entry is so that any alteration inside the premises do not disconnect the actual extraneous-conductive-part.
N.B. there is also a point of entry on the outside of the building.
But are the pipes extraneous-c-ps?
That's not logic.
It's nothing to do with the boiler.
It's nothing to do with the boiler - but the exposed-c-ps in the bathroom and the impedance between the extraneous-c-ps.
You would still need to inspect it.
Malc.
The fundamental point here is that you do not understand what you are trying to achieve - even after John's usual detailed and polite explanations.
If your radiators have NO connection to earth anywhere, it is better that way.
Working out convoluted solutions to problems which don't exist will make the situation worse.
Another solution instead of supplementary bonding in bathrooms would actually BE to insert a length (a metre is generally good enough, I think) of plastic pipe in all the runs to the bathroom thus negating the need for supplementary bonding altogether.
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