Earthing a steel bath

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 something heavier.
PoP
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Off the top of my head, I think it is 10mm or, if you have PME, 16mm.
Colin Bignell.
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According to my OSG (one before the latest one) then the size of supplementary bonding cnductors depends on the size of the (presumably incoming) CPC.
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 protected.
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).
--
Chris Green ( snipped-for-privacy@x-1.net)

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547-03-03 4mm if there is no mechanical protection, 2.5 mm if there is. Neil
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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.
Christian.
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supplied
So having plastic or flexible tails to the to baths taps exonerates supplementary bonding then?
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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.
Christian.
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to
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.... isolation.
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.

no
shock.
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Eh? The flexies that I've used have all had metallic braid down their length, and connected to metal at each end:
http://www.screwfix.com/app/sfd/cat/pro.jsp?idg794&ts6877
PoP
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wrote:

Sorry, some are non-metallic.
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well....
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.
Christian.
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At 0.5 - 3 umhos per cm, I wouldn't worry about it.
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"Christian McArdle" wrote in message

I agree with you. Paul Cook's definitive article on the subject, which can be found at http://www.iee.org/Publish/WireRegs/EarthingPlasticPipes.pdf , 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.
--
Andy



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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 required.
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On Fri, 5 Dec 2003 11:54:42 -0000, "Christian McArdle"

It'll be the supply via metal pipes that forces the bonding.
PoP
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