"Z" wrote in message
...
In article , Adrian Simpson
writes
A quick question on bathroom earth bonding if I may.
I'm in the process of refitting the bathroom, and all being well will
replace the bath this week. Originally the plumbing was all in copper,
and there is a steel bath. The plumbing is being replaced with plastic
(*), and the new bath is acrylic. Since there is there is very little
in the way of metal, do I have to bond it.
(*) the shower will have metal plumbing where visible (plastic where
not), but is driven from the boiler (i.e. is non-electric).
Adrian
All electrical fittings must be supplementary bonded with extraneous
conductive parts. That is light, shower, radiator, bath taps, bath (if
connected to ground eg via lead waste pipe), basin taps, basin (if
metallic eg stainless steel and connected to ground via for instance
lead waste pipe) must all be connected with one continuous earth cable
which should NOT be connected to the earthing terminal.
Electrical fittings yes .. but taps & wastes - no.
The IEE article I have on this system that supplementary bonding must NOT be
done when plumbed out in plastic, and to do so could make it dangerous.
I quote "... short lengths of metal pipework supplied by plastic pipes or
metal taps connected to plastic pipes, metal baths supplied by plastic pipes
and with a plastic waste do not require supplementary bonding."
Text of the report is as follows
:
Earthing Plastic Pipes
by Paul Cook of the Institute of Electrical Engineers
You do not have to earth plastic pipes
Plastic pipes make for a safer electrical installation and reduce the need
for earthing. Festooning an installation that has been plumbed in plastic
pipe with green and yellow earth wire is not necessary and of likely to
reduce the level of electrical safety of the property, not increase it.
Everyone knows that water and electricity do not mix, that the risk of
electric shock is greater when there is water around. They know that the
risk and severity of an electric shock is increased as a result of the
presence of water. This may be the reason for the concern that water
In plastic pipes may conduct electricity and that bonding is required.
Because of this, the IEE commissioned the Electrical Research Association to
carry out measurements of the electrical conductivity of water in plastic
pipes.
The ERA tests confirm that tap water in a plastic pipe is a poor conductor
of electricity. One metre of 15mm diameter of plastic pipe filled with tap
water from Leatherhead where the ERA are based, has resistance of 100,000
Ohms. This one metre of 15mm pipe will restrict currents to less than fatal
values and of course in practice, there would be many metres of pipe between
metal items of plumbing equipment and earth.
The resistance of water varies around the country, it is reduced by
impurities, not all of which are harmful. The additives put into water of
central heating systems to reduce corrosion make the most difference, as can
be seen from the table below.
Resistance - Ohms
15mm diameter, tap water 115.000
20mm diameter, tap water 65,000
15mm diameter, tap water with
double dose of inhibitor at 60°C 20,200
So why do wet hands and immersion in a bath increase the risk of electric
shock?
The human body plus clothes, particularly shoes has an impedance of about
3,000 Ohms - see next table. At 230 volts this will result in a current of
about 153mA (153 thousandths of an amp). This is not nice, but is unlikely
to kill you. If there are no shoes and hands are wet, the impedance falls to
500 Ohms and the current at 230 volts is 460mA.
This is getting decidedly unpleasant. Immersion of the body in a bath, in
effect halves the impedance of the body and current at 230 volts would be
then 1,000 mA. This is dangerous, and can kill.
Siliation
Body Impedance Current at 230 V
Dry with shoes3000 + Ohms 76 mA
Dry 1500 Ohms 153 mA
Wet 500 Ohms 460 mA
Body 1/2 immersed250 Ohms 920 mA
Horny dry hands and feet are quite good insulation. However, if the hands
are wet, salts and contaminants improve the contact and reduce the
resistance of the skin. Dry skin has a high resistance, wet skin has a
relatively low resistance.
The other reason why bathrooms and such places are relatively risky
electrically, is the presence of earthed metal. Should you be unfortunate
enough to touch the lie parts of broken equipment and nothing else except
say a well insulated floor, there would be little result.
Electrical
jointers and fitters regularly work live under such controlled conditions.
However if you touch a live part and an earthed metal pipe, then you get a
very dangerous electric shock.
An earthly environment where there are lots of metal pipes is potentially
less safe than an earth free environment. We can now start to see why
plastic pipe installations are going to lead to safer installations.
For a start, there is not all that earthed metal around.
The bonding requirements for plastic piped and metal pipes installations is
described below.
At the Service Position - Main Bonding In each electrical installation, main
equipotential bonding conductors (earthing wires) are required to connect to
the main earthing terminal for the installation of the following:
metal water service pipes
metal gas installation pipes
other metal service pipes and ducting
metal central heating and air conditioning systems
exposed metal structural parts of the building
lightning protection systems
It is important to note that the reference above is always to metal
pipes. If the pipes are made of plastic, they do not need to be main bonded.
If the incoming pipes are made of plastic, but the pipes within the
electrical installation are made of metal, the main bonding must be carried
out. The bonding being applied on the customer side of any meter, main
stopcock or insulating insert and of course to the metal pipes of the
installation.
The connections of the bonding wired to the pipes has to be made with a
proper clamp to BS 951 complete with the label "SAFETY OF
ELECTRICAL CONNECTION - DO NOT REMOVE."
If the incoming services are made of plastic and the pipework within the
building is of plastic then no main bonding is required. If some of the
services are of metal and some are plastic, then those that are of metal
must be main bonded.
In the bathroom - Supplementary Binding
Supplementary or additional equipotential bonding (earthing) is required in
locations of increased shock risk. In domestic premises the locations
identified as having this increased shock risk are rooms containing a bath
or shower (bathrooms) and if you are lucky to have one, in the areas
surrounding swimming pools.
Please note, there is no specific requirement to carry our supplementary
bonding domestic kitchens, wash rooms and lavatories test do not have a bath
or shower. That is not to say that supplementary bonding in a kitchen or
wash room is wrong (it would be wrong for plastic pipes!) but it is not
necessary.
For plastic pipe installation within a bathroom the plastic pipes do not
require supplementary bonding and metal fitments attached to these plastic
pipes also would not require supplementary bonding.
It seems to to be the practice of some builders to effect all the plumbing
in plastic except for those bits of the pipework that are visible.
These short lengths of metal pipework supplied by plastic pipes or metal
taps connected to plastic pipes, metal baths supplied by plastic pipes and
with a plastic waste do not require supplementary bonding.
However, electrical equipment still does require to be supplementary bonded
and if an electric shower, or radiant heater is fitted, they will require to
be supplementary bonded as usual.
This requirement does not apply to class II or all insulated equipment where
no metal work that is likely to become alive in the event of a fault, is
accessible. However, it is recommended that supplementary bonds are run to
the earth terminals of all electrical equipment accessories e.g. flex
outlets, or the equipment itself, as class II equipment may be replaced by
class I during the life of the installation.
General on Supplementary Bonding for bathrooms:
Metal radiators supplied by plastic pipes should not be supplementary
bonded. It is safer not to supplementary bond them. Locations generally are
safer if the location is earth free as discussed earlier.
Metal (class I) items of equipment (e.g. electrical heaters and showers)
require supplementary bonding if simultaneously accessible. Supplementary
bonds to be connected to the protective conductors of each circuit at the
accessory point.
Supplementary bonding of short lengths of copper pipe (less than 0.5m in
length) installed where the pipes are visible, is not necessary.
Supplementary Bonding is carried out to the earth terminal of equipment
within the bathroom with
exposed-conductive part. A supplementary bond is not run back to the main
earth
Metal window frames are not required to be supplementary bonded unless they
are electrically connected to the metallic structure of the building
Metal baths are supplied by metal pipes do not require supplementary bonding
if all the pipes are bonded and there is no other connection of the bath to
earth.
All bonding connections must be accessible and labelled
"Safety Electrical Connection - Do Not Remove".
The full article with diagrams is available from Hepworths at:
http://www.hepworthbp.co.uk/Pages/Hep20frame.htm
click on the link to earth Bonding