Central Heating Earth Bonding

[Harry Willis]

As a CORGI registered installer, I have been podering upon the stated need
for cross bonding between the pipes connected to a newly installed gas
central heating boiler.

Assuming a typical UK domestic household, where the services are correctly
connected to earth as close to the entry point of the dwelling. I install a
new central heating boiler. With the make of boiler I install, the central
heating flow / return, hot / cold water and gas pipe are connected to metal
compression fittings that are in turn mechanically fastened to a metal
bracket that forms part of the boiler's casing.

It seems to me that this metal to metal contact between all of the pipes is
better and more robust than using earth bonds and a cable connecting them.
It is possible that the earth cable or bonds could become slack, or due to
the possibility of corrosion, become less effective. The metal bracket of
the boiler is a solid piece of equipment and to me, provides a more than
adequate cross bond between the connected pipes.

Comments?

 

[sQuick]

As a CORGI registered installer, I have been podering upon the stated need
for cross bonding between the pipes connected to a newly installed gas
central heating boiler.

Assuming a typical UK domestic household, where the services are correctly
connected to earth as close to the entry point of the dwelling. I install
a new central heating boiler. With the make of boiler I install, the
central heating flow / return, hot / cold water and gas pipe are connected
to metal compression fittings that are in turn mechanically fastened to a
metal bracket that forms part of the boiler's casing.

It seems to me that this metal to metal contact between all of the pipes
is better and more robust than using earth bonds and a cable connecting
them. It is possible that the earth cable or bonds could become slack, or
due to the possibility of corrosion, become less effective. The metal
bracket of the boiler is a solid piece of equipment and to me, provides a
more than adequate cross bond between the connected pipes.

Comments?

Cross bonding is usually done in close proximity to areas that could
have a different potential to earth.

Even though the system you have just fitted is very well bonded to
the metal of the boiler, what if someone was to fit some form of
plastic coupling in the system.....

That's why bonding is usually done around areas that you are likely
to have contact with.

sQuick...

 

[John G]

As a CORGI registered installer, I have been podering upon the stated
need for cross bonding between the pipes connected to a newly
installed gas central heating boiler.

Assuming a typical UK domestic household, where the services are
correctly connected to earth as close to the entry point of the
dwelling. I install a new central heating boiler. With the make of
boiler I install, the central heating flow / return, hot / cold water
and gas pipe are connected to metal compression fittings that are in
turn mechanically fastened to a metal bracket that forms part of the
boiler's casing.

It seems to me that this metal to metal contact between all of the
pipes is better and more robust than using earth bonds and a cable
connecting them. It is possible that the earth cable or bonds could
become slack, or due to the possibility of corrosion, become less
effective. The metal bracket of the boiler is a solid piece of
equipment and to me, provides a more than adequate cross bond between
the connected pipes.

Comments?

It is a long time since I worked with compression fittings but if my
memory is correct then the compression rings are nylon or some such so
the electrical contact will not be as good as you might imagine.

 

[daestrom]

As a CORGI registered installer, I have been podering upon the stated need
for cross bonding between the pipes connected to a newly installed gas
central heating boiler.

Assuming a typical UK domestic household, where the services are correctly
connected to earth as close to the entry point of the dwelling. I install
a new central heating boiler. With the make of boiler I install, the
central heating flow / return, hot / cold water and gas pipe are connected
to metal compression fittings that are in turn mechanically fastened to a
metal bracket that forms part of the boiler's casing.

It seems to me that this metal to metal contact between all of the pipes
is better and more robust than using earth bonds and a cable connecting
them. It is possible that the earth cable or bonds could become slack, or
due to the possibility of corrosion, become less effective. The metal
bracket of the boiler is a solid piece of equipment and to me, provides a
more than adequate cross bond between the connected pipes.

Comments?

Some types of compression fittings are metal/metal, and you're right that
would be a pretty good electrical connection. But the system will be
maintained for quite some time, and not always by someone with an
*electrical* background. As the others have suggested, not all couplings
are 'equal'. Plastic or some non-conductive sealant used in the joints
could compromise the electrical conductivity. So, apparently, the UK 'rule
makers' have decided it is safest to have a second, bonding wire cable.

daestrom

 

[Andrew Gabriel]

As a CORGI registered installer, I have been podering upon the stated need
for cross bonding between the pipes connected to a newly installed gas
central heating boiler.

There is no such requirement in the UK electrical regs unless
the boiler is fitted in a room containing a bath or shower.
Some trade bodies (such as CORGI in this case) sometimes
specify their members should do things which are not required
by the regs. I don't know if this is the case here as you have
not said where you saw this need 'stated'.