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Central Heating Earth Bonding

Discussion in 'Electrical Engineering' started by Harry Willis, Oct 11, 2005.

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  1. Harry Willis

    Harry Willis Guest

    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.

  2. sQuick

    sQuick Guest

    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.

  3. John G

    John G Guest

    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.
  4. daestrom

    daestrom Guest

    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.

  5. 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'.
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