Earth Bonding

Yet again, I need some advice!!!!!
In my new bathroom I have plumbed-in a sink, bath and shower. Th pipes for the bath are copper and run under the floorboards and surfac under the bath. I have joined to these with plastic pushfit pipe an then into 22mm flexible tap tails onto the taps. The total length o platic pipe on this run is c. 0.3m. For the basin, I had to run a new plastic pipe for about 1.5m whic joins to a chromed 15mm pipe feeding the basin tap tails. For the shower, I have run copper pipe chased into the wall and tile over from the loft down into the power shower unit. In the loft where they surface these pipes are connected to the HW cyliner and C tank using plastic pipe.......
Do I need to Earth bond any/all/none of these to prevent killing me, m wife or my children???
Oh yes..one more thing....how do I actually Earth bond them if I nee to - on the copper pipes under the bath I carefully replaced two Eart Clamps from the pipe, but they do not actually seem to be connected t anything......I'm still a DIY novice (although getting more confident are simply dont understand what those clamps ACTUALLY do!!!??
-- alexbartman
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They aren't supposed to be connected to anything else necessarily, the idea is to ensure that every exposed bit of metal is connected together so you can't get a shock by touching two of them.
The basic requirement of the IEE regs is that all exposed conductive 'things' in the bathroom are connected together. You don't have to include in this things like door handles and other small items unless they have a significant chance of getting electricity connected to them. (e.g. you do have to earth bond any bits of metal associated with lights or other electrical fittings).
--
Chris Green

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snipped-for-privacy@isbd.co.uk wrote:

Prior to this week's bathroom refit the two sink taps were bonded together (by the previous occupier), and so were the two bath taps, which also were connected to the radiator - ie there were two separately connected 'zones'. (Although there was and is continuous copper pipe throughout).
Since redoing the bonding this week, the whole lot are now connected together (see my thread on the subject!), which I thought was necessary according to current regs. But given that it wasn't possible to put one hand on the bath tap and the other on the sink, was my previous setup actually legal and safe as it was?
David
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alexbartman wrote:

Start by reading and inwardly-digesting the authoritative article on the subject, whose pictures also appear in the IEE On-Site Guide:
http://www.iee.org/Publish/WireRegs/EarthingPlasticPipes.pdf
On this basis, you don't need to bond the basin tap tails: there's a "long" (1.5m) length of plastic pipe between them and the incoming metallic pipework. There's nothing else which could introduce mains voltage (or related Harmful Potential) to those, is there. (Is there?)
The bath taps are 'almost' as isolated: though the length of plastic is only 0.3m, it's got ordinary water, not CH-water-with-inhibitor, so the resistance of this stretch of water is (according to the article's figures) about 30k, two of these in parallel is still 15k. BUT you didn't tell us whether the bath's metal or plastic, or if its waste is metal (unlikely in anything newish). Either of those would make me keener on bonding one of: the bath, the taps, or (if metallic) the waste, especially if it's conceivable that the main metal pipework feeding the bath could come into physical contact with the bath metalwork. OTOH, if the bath's plastic, and the waste is too - leave the taps alone.
The shower - now, there you have a "power shower unit", which is electric, right (a pump rather than an instantaneous heater, yes?) So the all-metallic pipe run from pump to shower does need to be bonded.
But, we ask, bonded to *what*? "To all the other metallic things which are capable of introducint a potential, including a (proper, low-resistance) earth potential."
You see, BONDING IS NOT EARTHING.
EARTHING IS NOT BONDING.
BONDING IS NOT EARTHING.
EARTHING IS NOT BONDING.
The *point* of bonding is to make EXTRA SURE that ALL of the conductive metallic surfaces WHICH COULD BE AT DIFFERENT POTENTIALS are in fact going to be at the SAME potential. And, therefore, no-one will get a shock from them if they touch two or more of them at the same time, even in the presence of a fault.
So, we don't care about a radiator fed by plastic pipework (even if it has decorative chrome or copper pipe right by its tails), since it's not going to be at any 'interesting' potential. In your case, that's the argument by which we don't care about your basin taps, or your assumed-plastic and/or far-from-metallic-pipework bath.
So, we want to bond those shower pipes to any other potential-introducing metalwork. Well... is there any? The picture on p.3 of the IEE article shows some common (and less common) ones - the most obvious being yer bathroom light (or 'luminaire' as we likes to call them in Regs-speak ;-) and a shaver socket. Other examples could be, in a large bathroom, the washing machine and tumble-dryer you have connected by fused-connection-units (never plugs in a bathroom!).
As a practical matter, you don't have to have a highly obtrusive and visible green-n-yellow wire clamped to the shower pipes right next to the controller, though. It's OK to put the clamps on the pipes in the loft close to where they enter the bathroom, and connect the bonding wire from there to the (say) shaver socket - either directly, or (again more nicely) to the E terminal of the junction box which feeds the shaver socket and the bathroom light and fan. (The Regs say it's OK to use the 'earth wire' - the Circuit Protective Conductor - in the cables feeding those items as the bonding conductor. But you do have to bond to them in or close to the bathroom - no fair saying 'they're all bonded back at the consumer unit'!)
This does raise the corner case where there's only a single potential-introducing point in a bathroom - e.g. the all-plastic world of pipes, non-metallic luminaire(s) with pullswitches, and just the one (metal-faced ;-) shaver socket. In this case there's nothing to 'bond to', since supplementary bonding means extra wiring to electically join two or more potential-introducers. What's Good Practice in this case, eh? ;-)
Anyway - hope that, together with the IEE article, helps. If you're left with doubts, get a sparks in. They may well say things which disagree with the IEE article and with what I've said, mind: the whole topic of bonding is imperfectly understood, with some pros insisting on festooning bathrooms (and kitchens!) with festive displays of green-n-yellow (and in some extremes running it back to the main earthing terminal). If you ever explore the IEE Forum where those pros (and hangers-on) with time on their hands argue back and forth about The Regs, you'll find supplementary bonding being one of the recurrent topics of heated debate...
Stefek
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Stefek Zaba wrote:

Blimey, just when I thought I'd got my head round the requirements I read your bit above about connecting the bonding to the CPC! I'd thought that was a complete no-no! So this is only required if you have metal electrical fittings in the bathroom?

Right - so in my case the only exposed metal in the electrical fittings are the screws holding on the shaver socket faceplate. Which means there's a theoretical risk of somone being electrocuted via one finger on a screw head and the other on the basin tap, am I right? But isn't the risk of this so small that it would be outweighed by the 'risk (is there one?)' of connecting the bathroom bonding to the CPC?
David
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Lobster wrote:

Nah. It's not a complete no-no: "bonding is not earthing" doesn't mean that the bonding *mustn't* be earthed, just that its point is about equalising *local* potentials in the bathroom, rather than providing a low-resistance earth path. In practice your bathroom bonding is practically always earthed, as the metallic-things-which-might-introduce-a-potential will themselves be earthed.
The IEE guidance on CPC bonding is that it should be done even if the equipment and wiring accessories are currently all-insulated, to allow for later changes in what's connected.

If your basin taps are connected by metal pipework running throughout the house - yes, they want supplementary bonding. The CPC in the shaver socket is supposed to be supp-bonded anyway. The 'what if there's only one thing, what does that bond to?' question I raised is a theoretical corner-case, really - most of our bathrooms have more than one electrical item in them anyway - although it does then get to be a bit of an argument about whether the existing CPCs themselves provide adequate bonding in the case where all the accessories are on the one lighting circuit and all the cable connections are made in or close to the bathroom!
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Stefek Zaba wrote:
Thanks for your responses to my queries in the later post in this thread... OK, I gather I now have to extend my new bonding to include the shaver socket then!

I already have clamps up in the loft, on the H&C pipes feeding the shower; they are a few feet away from the jct box which provides the feed to the shaver socket. Now - what is the correct way of wiring a stonking great earth bonding cable into the 20A junction box!!??
Thanks David
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Lobster wrote:

Up in the loft, away from danger of mechanical damage (so clip it to the side of joists if need be), the supplementary bonding conductor from yer nearest pipe clamp to the shaver-socket JB (or other JB intimately related to the things in the bathroom running off the lighting circuit) needn't stonk ;-) It'd be acceptable, but skirting the shoals of bodgeology, to use a length of 1mmsq/1.5mmsq lighting T&E with the L and N conductors clearly cut short, using only the CPC. If all you have is the 6mmsq or 10mmsq you've used for the rest of the supp bonding, you have the choice of cutting short 4 or 5 of its strands (not such a good plan, as it's too easy to nick the remaining strands and have your bond fail in a few years time) or arrange a transition through one way of a 30A chockblock to a very short length of CPC-core or similar, suitably sleeved, and clipped in place just next to the JB...
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On Fri, 21 Jan 2005 19:05:12 GMT, Lobster

Well, stonking is an overstatement. Change the JB for a 30A and the 4mm earth will fit in with loads to spare.
--

SJW
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Lurch wrote:

It would, wouldn't it; just that the 20A one is a 4-terminal one as it has a switched live for the bathroom fan/light, and the outgoing circuit cable goes to the shaver socket.
That being the case, do you subscribe to the Stefek Method, which would be easiest!? Or should I interpose a 30A JB in the cable heading to the shaver socket, and wire my bonding cable into that? Or summat else?
David
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On Fri, 21 Jan 2005 20:59:19 GMT, Lobster

I knew you were going to say that!

Hmm, bordering on bodging there TBH. It'd work though.

That would work, and it's not a border line bodge. ;-)

Can you not pull the cable up the wall from the shaver socket with a new 1mm T&E and 4mm earth attached? (NB: two man job unless it's nice and slack and you need to be good at tieing on wires!)
--

SJW
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Lurch wrote:

Guilty as charged - I didn't feel all that good about mentioning those approaches in public, though I'm sure many of us have done similar, at least in our ignorant and wayward youth ;-) The 'legit' route of going through a 30A JB is less bodgy than the others, for sure...
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Stefek Zaba wrote:

If it's junction box terminal capacity that's the problem, rather than wiring space, you could legitimately (IMO) trim two or three strands off the end of the 4mm^2 wire. This only reduces the CSA of the supp. bonding conductor in a space where there is mechanical protection, in consequence of which the CSA only needs to equal that of the smaller CPC being bonded.
--
Andy

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