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
Dave - The Medway Handyman
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
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.
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
Dave, The electrical resistance of water is here
Although this will not fully answer your question.
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 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).
 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
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.
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.
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
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? :-)
This message has been rot13 encrypted twice for added security
?? 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
[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
A bonded bathroom is, within its normal working conditions, a
sufficient approximation to a Faraday Cage. Full stop.
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
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