Earth Bonding?

Just curious.
Saw an installation (wash hand basin) where the copper pipes came out of the wall into plastic push fit elbows, then a short run of copper, then plastic push fit tap connectors.
The earth bonding cables were connected to the copper pipes between the plastic elbow & plastic tap connector.
Looking at it, the cables seemed 'isolated' from the taps & pipes by the plastic fittings, then I realised that the pipes are full of water.
Is that how it works? Would it still protect if the system were drained down?
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Dave - The Medway Handyman
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On Sat, 28 Jun 2008 09:24:55 +0000, The Medway Handyman wrote:

This is an example of gold plated compliance with the regs. No supplementary bonding is needed if there's less than 0.5m of Copper pipes in the supply.
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Ed Sirett - Property maintainer and registered gas fitter.
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No. Tap water doesn't conduct electricity that well.
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The Medway Handyman wrote:
Spose I better say it before someone else does...
No such thing as "earth bonding". There is earthing, and there is equipotential bonding (main and supplementary), but they serve different purposes.

Kind of pointless. Note that if you are complying with the 17th edition there is no longer a requirement for supplementary bonding in rooms containing a bath or shower. A room with just a hand basin and a loo say, did not require it under the 16th edition either.

No, just someone getting a bit overenthusiastic.
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The best I have seen is a full plastic pipework job for a loo and sink job and someone had put clamps around the tap tails and bonded the taps together!
Dave, The electrical resistance of water is here
http://www.hep2o.co.uk/bititesguideearth.htm
Although this will not fully answer your question.
Adam
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John Rumm wrote:

Could you expand on that John - or point me to somewhere I could read up on it?

So, would these bonding wires be better if they were connected to the copper pipes coming out of the wall?
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The Medway Handyman wrote:

Good earthing will ensure that in the event of a fault the supply can be disconnected quickly by providing a path for a large fault current to flow - hence causing rapid operation of a Circuit Protective Device. It will also limit the voltage rise of anything earthed that you can touch to a safe level (under 50V typically) during the fault. So if a live wire falls off the inside of your washing machine and makes contact with the case, the big fault current will open the fuse in the plug or circuit breaker on the circuit quickly, and should you also happen to be touching the machine at the time, the voltage you are exposed to should be low enough to not place you at significant shock risk.
Supplementary equipotential bonding is not designed to clear a fault condition, or limit the absolute touch voltage. What it is supposed to do is electrically tie together any pipe or service or other part that could under fault conditions introduce a dangerous potential into the room. In doing this it attempts to create a Faraday cage - where anything and everything that you can touch will be at the same electrical potential[1] as everything else - even if it is elevated way above true ground. So for example a fault that could leave a hot tap at 230V due to it being connected to a faulty inline water heater, and a well earthed cold tap connected directly to a rising main, would pose a serious shock hazard - touching both taps would expose you to a 230V potential difference and a "stiff" supply. If the taps are bonded together (and anything else that may take on an elevated voltage under fault conditions like the earth wires of any circuits feeding power into the room), there is the possibility that both taps will rise to 230V under fault conditions - however touching both exposes you to zero volts of potential difference. (equipotential zones only work well where you are insulated from any true earth reference - its no good making sure that all the taps float up to the same voltage if you are standing on something that is conductive and is going to stay put at 0V).
[1] in reality the bonding may fail to tie all elements together at exactly the same potential, however it must limit any potential difference to 50V or under.

There are a range of possible answers to this depending on circumstance.
Generally with plastic pipe installations, supplementary bonding of the pipes is not required (although it may be required between the earths of say lighting and power circuits if they are both accessible in the room plus any other extraneous metallic parts (CH Pipes for example)).
In rooms which are not "special locations" (i.e. places likely to put you at increased danger from electric shock (typically because you might be wet)), there is also no requirement. So for example a cloakroom with loo and sink would not require it )although it is commonly seen in such circumstances).
Under the 17th edition it is also sometimes permitted to have no EQ bonding in a room with a bath or shower providing that the main EQ bonding is in place, and all the circuits feeding the room have additional protection from a RCD with 30mA (or lower) trip threshold.
The one you would need to take care with is where you have say a bathroom where there is some quantity of exposed copper that is in turn connected to plastic pipe and then the taps. If the exposed pipe is likely to be accessible then it could pose a risk an should be bonded, even if the taps don't since they are isolated via plastic pipe.
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John.

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Now this answer is a example of why this group is so good. I knew quite a lot of what is in it, but I don't think I have ever seen such a concise and comprehensive summary of the subject, and moreover written in plain English. Thanks John!
Charles F
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CJF wrote:

I'll second that. Thanks John, I am a wiser man.
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None the wiser, I suspect, but hopefully better informed :o)
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Bob Mannix wrote:

:-)
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On Sun, 29 Jun 2008 04:50:38 +0100, John Rumm wrote:
Great explanation John - it would make a good wiki article, say "Earthing and Bonding".
Couple of points/clarifications. Faraday Cages are about shileding the enclosed space from electrical fields rather than about electrical safety:     http://en.wikipedia.org/wiki/Faraday_cage Anyway it's not an everyday concept so doesn't help explain something to the Ordinary Joe in the street.

"stiff" supply? You mean a) a low impedance supply, or b) a supply that turns you into a stiff? :-)
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John Stumbles wrote:

Prolly not a bad idea...

yup there are better explanations with more general appeal...

Yes, and quite possibly yes! ;-)
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Um, no it doesn't.
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Huge wrote:

I know what he meant. It isn't a Faraday cage (RF field densities at mains type voltages? OUCH!) but generally, great post, thanks John.
Andy
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Oh, me too ...
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wrote:

There is no such thing as a perfect faraday cage. Most let some EM radiation through of some sort. At 50Hz the one described will do nicely.
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A Faraday cages is a closed conducting surface enclosing a space from which it excludes static electric fields. Its effect on EM radiation is (a) secondary and (b) partial.
Ian
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?? what has EM radiation got to do with it?
the Faraday Cage efffect is an observation about electric fields (with or without an associated magnetic field) and conductors.
the wikipedia article [http://en.wikipedia.org/wiki/Faraday_cage } is decidedly unsatisfactory. It goes overboard with examples from HF - off beam if not OTT


that's very close to it. However mentioning "static" in the definition misleads. A better definition is:
Faraday Cage: a space enclosed by an envelope which is a perfect conductor. (A perfect conductor being one with zero conductance between any 2 points.).
By definition the electric field gradient across such a space, between any 2 points on the envelope, must be zero. Shielding from external electric fields becomes a consequence of the definition, not some magic property.
[Nor is there strictly any requirement that the "space" should be a simple 3D volume nor that the envelope is a closed surface - but that is an excursion into topology.]
A practical attempt to build a Faraday Cage is never going to be 100%. What we have to do, as in any engineering project, is come as near as possible without over-engineering.
In the case of a bathroom, field frequencies are zero (ie DC) or low frequency (ie 50Hz or possibly higher if transformers or electronic voltage converters are present). Bonding every conductor in sight is sufficient to achieve a satisfactory approximation to a Faraday Cage. The electric field gradient between any 2 possible contact points is zero (or near enough) & the wet bather is protected from shock.
Its effect on EM radiation

& irrelevant
A bonded bathroom is, within its normal working conditions, a sufficient approximation to a Faraday Cage. Full stop.
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jim wrote:

Sorry it isn't; it's an equipotential zone in which there won't be dangerous potential differences (at power frequency) between certain items of metalwork. That's all. A static or slowly changing charge placed outside the zone would still result in a corresponding electric field inside the zone, unless there's an awful lot or pipework, or the walls, floor and ceiling happen to be conductive. Any Faraday cage effect is purely incidental, and largely irrelevant to the purpose of the bonding.
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