|
Plastic
does not conduct electricity and the implications for electrical
earth bonding are a common cause of confusion. In most cases the
use of plastic pipe eliminates the need for earth
bonding.
-
The
following comments assume that the gas pipe to the boiler is
metallic; that hot and cold water services; central heating
pipes; and waste pipes from the bath, hand basin, WC, bidet,
and kitchen sink are plastics.
-
Under
such circumstances there is no requirement to supplementary
bond: the bath, even if metal; the kitchen sink; or central
heating radiators.
Bathroom radiators and towel rails heated by a wet central heating
system do not require supplementary bonding unless there is
less than a two metre run of plastics pipe between them and
the boiler, or between them and any metallic pipe from the boiler
to which the radiator plastics pipe is connected.
-
There
is no requirement in the above circumstances to bond a steel
sink, but it is not wrong to bond a steel sink to the earth
terminal of an adjacent socket.
-
If
all the conditions in (I) above are met, then the following
must be bonded:
Main
Bonding
The
consumer's gas pipe at the service entrance; any other services
which are metallic e.g. heating oil pipes; structural steel should
all be bonded to the main earth terminal.
|
Supplementary
bonding
In
the bathroom, the earth terminal of the lighting point (rose, luminaire
coupling, luminaire), the earth terminal of the electricradiant
heater (if any), the earth terminal of the electric shower heater
(if any), the earth terminal of any other appliance in the bathroom
should be supplementary bonded together. There is no need to connect
the supplementary bonding conductor to the main earth bar.
-
If an instantaneous water heater (shower or over sink) with an
uninsulated element in contact with the water is to be installed,
as well as the circuit protective conductor, a separate duplicate
4mm² green/yellow conductor must be installed and connected
to the heater earth terminal and the main earth terminal or bar.
If in doubt contact the heater manufacturer or importer.
Where
the conditions in (I) do not apply the installation must be considered
on an individual basis.
The
above arrangements relate specifically to true plastics pipe systems
and do not apply to plastic coated metallic pipes.
In
summary, in most cases less bonding is necessary with plastics pipes
than with metal pipes, but it is important to follow the guidelines
set out above. If in doubt, the best advice is to consult the manufacturer
of the pipes being used or a fully qualified electrical engineer.
The
'On Site Guide' published by the Institution of Electrical Engineers
incorporates clear guidelines on electrical bonding for plastics
plumbing systems and highlights the benefits which they offer in
this context.
Copies
of the IEE On Site Guide are available from the IEE Bookshop, Savoy
Place, London WC2R 0BL.
Tel:
01438 767328.
|
