I've got the 16th edition wiring regs here so I can probably look it
up. However does anyone know off the top of their head what the
minimum diameter earth wire is for earthing a steel bath? This steel
bath will have one of those electric shower units installed over (it's
already there - I'm replacing the fibreglass bath).
I've got 4mm earthing cable to hand but I'm wondering if I need to get
According to my OSG (one before the latest one) then the size of
supplementary bonding cnductors depends on the size of the (presumably
Where it's just bonding "extraneous conductive part" to "extraneous
conductive part" mechanically protected conductors need only be 2.5sq
mm and not protected ones 4.0 sq mm.
Where it's bonding "Exposed conductive part" to "Extraneous conductive
part" it's generally one size less than the CPC for mechanically
Where it's bonding "Exposed conductive part" to "Exposed conductive
part" then it's generally the same size as the CPC.
Extraneous parts are conductive things you can touch which aren't bits
of elextrical equipment. Exposed parts are bits of electrical
equipment which should be earthed already. You only have to
supplementary bond between things which can be touched simultaneously.
Some things are explicitly not required to be bonded - e.g. metal
windows and metal handrails. It's also not required for metal parts
supplied by plastic pipes (including a bath).
Remember that you should only supplementary bond a bath when it is supplied
by metal pipes, or touches a metal part of the building structure. If
neither applies, it is safer NOT to bond the bath.
Yes, although just a short insulating break isn't enough, the supply has to
be substantially plastic. I doubt that 20cm of tail before hitting copper
would be enough, although I'm not sure on this.
However, they are clear to state that safety is REDUCED by bonding a bath
fed by plastic only. The IEE suggest that the safest bathroom is one with no
supplementary bonding at all, because there are no potentially earthed
services or surfaces present, making it difficult to get an electric shock.
However, if such earthed services have to be present, then supplementary
bonding is a necessary evil.
Flexible bath/basin connections are non-metallic. Having a 1 foot flex to
each tap must eliminate the need. 20 cm of plastic is enough as it isolated
the metal bath from the metal feeding pipes. isolation is well....
AIUI, supplementary bonding is just connecting the bath and basin taps and
bath earth lug to each other, not back to the meter pole, by a 4mm loop.
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As the water itself is conductive to a slight degree, there is a requirement
for the insulated pipe to be a certain length for sufficient isolation to be
achieved. A simple insulated break isn't sufficient. I don't happen to know
what the required length of plastic is, though.
I agree with you. Paul Cook's definitive article on the subject, which can
be found at
also supports this view, in that it states:
" [...] one metre of [plastic] 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."
By implication, lengths of plastic pipe significantly less than one metre
_might_ not restrict current to less than fatal values.
There is also the risk that, in the future, some over-enthusiastic
well-meaning person could come along and put bonding straps across your
short plastic sections in an attempt to restore "missing earths". If said
person didn't spot that the local supplementary bonding had been omitted
then a much greater potential danger would be created.
Conclusion: where there are only short insulating sections to taps, etc.,
bond (per OSG) as for a metal pipe installation.
Well, apart from the fact that 'exonerates' isn't the right word I
don't think - yes. If you have plastic pipe plumbing then bonding of
metal bits at the end of the pipes (including the bath) isn't
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