**Supplementary** bonding is currently only required in bath and shower rooms, where they should be bonded. This is governed by a different regulation to that for **main** bonding which is where the CH bond is required.
Hope that makes sense (My explanation, not the reasoning behind the regs!)
They would not require bonding under the main equipotential bonding rules as, being insulated, they do not qualify as "extraneous conducting parts" - the defintion for which requires that they are "liable to introduce a potential". (They would float)
However, a whole metal staircase indoors would require a main bond in my opinion.
I would concur. Although, obviously not everyone agrees or the IEE wouldn't have found it necessary to produce that document saying you don't have to bond plastic pipes!
It does. Unfortunately it doesn't parry with a comment by Christian
No, the guidance explicitly states that short lengths of visible metal pipework leading to an isolated plastic supply does not affect matters and that it is safer not to bond such appliances.
The basic underlying principle of the guidances is that isolation is best, but if it can't be guaranteed, then supplementary bonding is the second choice.
If the radiator has no way of being connected to (a possibly imperfect) earth, then it shouldn't be supplementary bonded. Note that any addition, such as an electric heating element in a towel rail, might be enough to require supplementary bonding, as it may introduce a non-floating potential to the radiator surface.
Christian.
Your short length of chromed pipe doesn't need supp. bonding. With a long length of plastic pipe feeding the rad, the resistance of that and its watery+inhibitor content is well high enough that the rad and chrome tails won't form an effective conducting path bto/from other parts of the house.
Only circumstance I'd be tempted to bond the rad is if there's one or more supply cables in close proximity - close enough that a rodent/heat-induced failure of insulation could make the rad or tails live. Pretty unlikely!
And as to the aesthetics - you can connect to the back of a rad out of sight, either by drilling a hole into the pressed fins (no, *not* the water-carrying parts ;-) and scraping off surrounding paint, or using a proprietary bonding clamp like the E-Z-Earth...
Stefek
I would agree with Stefek and Christian that the pipework itself does not need bonding, but I would take a slightly different view on the radiator itself, if it is metal.
However, the question I would ask here is if you are using plastic pipework, what other exposed metal parts are there in the bathroom that you need to bond the radiator to? Do you have a fixed appliance such as a heated towel rail etc?. Don't forget, local supplementary bonding in a bath/shower room is about connecting the parts in the zone **together**, not connecting them back to the earth bar. If you only have the radiator, it is not an issue as there is no other way a potential can be introduced into the zone, or if one is, then no path to earth.
So why would I bond the radiator? The idea is that if a conductive part becomes live in the zone, you do not want there to be a mechanism for another part to present a path to anything like earth via a person. In this case, if a wet person contacts both parts at the same time, the mains voltage from the exposed part can then pass through said wet person, said radiator then either of:
1) water in radiator to boiler metalwork to earth or; 2) wall to "true" earth (This is the reasoning behind why even relatively small exposed structural steel parts need to be bonded)In addition, the opposite situation also applies; i.e a fault in the boiler could introduce a voltage into the bathroom via the water in the pipes before the automatic disconnection was activated.
So, assuming there are other metal parts, in your situation, I **would** cross-bond the radiator. However, all said, I don't think it is a significant risk. No, the reason I would bond it is really the same reason I would main bond the central heating - so it won't fail an inspection! If you are worrying about this out of a concern about safety, then don't. It is not an real issue in your situation. But, the way I look at it, if you are going to do it to pass muster, you want to be satisfying all but the most picky inspectors. I would find it hard to find anything in the regs to use to argue against an inspector who took the view that a metal radiator could give a path to true earth. And remember, many electricians don't understand the rules properly, so you don't want to give them any excuses!
The bonding requirements for metal parts are, in my opinion, completely excessive. The exceptions where bonding is not required include "fixing screws of non-metallic parts" and "up to 50mm x 50mm nameplates", which gives you an idea of what they think *is* covered. To comply with the letter of the rules, a 6 cm square metal plate requires bonding! I don't bother with this sort of thing, because it can get silly. But in this case I think there is at least a reasonable case for complying.
Just my 2p
Hmmm. If you do bond such a radiator, where do you stop? If I understand what you're saying correctly then to comply with the letter of the regs then the following also might need bonding:
1) metallic wall units 2) soap dishes (very likely to be >5cm square) 3) towel rails (NOT heated ones) 4) mirrors with metal frame 5) shower enclosuresetc etc
if this is the case then I have never ever come across a bathroom in a house that has compliant supplementary bonding, and am in fact unlikely ever to come across one.
swmbo: "can you just put up that towel rail there, under the window" me: "ok, will do. I'll drill the tiles and fix it. oh, but I'll need to trail the supplemental bonding conductor across the floor, or alternatively remove the tiles, bury it in the wall, then rip up the floor (ceramic tiles) and run it to the bonding conductor" swmbo: "f*&? off! Just screw it to the wall"
I truly hope I've misunderstood something!!!
(and before some smartarse jumps in and says "and you wonder why Part P is being introduced", screwing a towel rail or toilet roll holder to a wall is not a controlled activity that requires building regs approval)
The IEE disagrees. Their policy is that bonding the radiator when it is already isolated reduces safety. If you've got one hand on the live, and another on the radiator, would you prefer the radiator to be a nice clean earth so you can get the maximum current through you, or would you prefer it to be completely isolated?
Indeed. Which is why supplementary bonding is a second best solution. It is better that there are no earths at all. If there must be earths then supplementary bonding at least ensures they are all the same potential.
Incorrect. The IEE did an extensive series of experiments to measure the impedence of water in pipework. Their conclusions were that 1m of plastic pipework had sufficient impedence to prevent dangerous currents flowing, even if corrosion inhibitor was installed. It was the results of this experiment that led them to make their policy that radiators and metal baths fed exclusively by plastic pipework and not touching structural metalwork, electrical appliances or other parts likely to introduce a potential should NOT be bonded. This isn't a case of "no need to bother to bond", but a case of stating that bonding in these circumstances REDUCES safety.
If it failed an inspection, I would be right on to them with the IEE guidance. I'm not going to reduce the safety of my bathroom by introducing dangerous low impedence earth potentials because of the ignorance of an inspector.
Christian.
Only electricity is a long way away, enclosed in the fitted units (for the whisper it 'macerator')
It's one of these fancy bathroom towel rails (not electric) and the mountings do not conduct to the mounting screws so I would have to bond to the pipe, which is nicely visible at head-height when sitting in the bath.
Thanks - that's exactly what I thought you meant and what I have implemented.
Given that argument, what are your views on the rules on visible structural metalwork - metal internal staircases, exposed RSJs (where fire risk not an issue), etc. Not so bothered about earthing these as it can be done invisibly but the "isolation is best" seems remarkably sensible to me provided there are no sources of electricity nearby.
I think this is the central issue - if it is isolated and that is going a question of degree rather than a yes/no.
Well, there wont be a live/earth situation if all the parts are bonded. Nothing to bridge - the purpose of local bonding.
But clearly, genuinely floating metallic parts and no possible source of live is preferable.
I would agree, but completely avoiding earths is extremely difficult. Hence my point about ground-floor bathrooms with solid floors. And wet too. Need I say more.
Now, that is news to me. I don't know about this work, and it puts a totally different angle on things. I would be very interested to read up on this, as would make things a lot simpler. Was this published?
Baths don't require bonding if fed by metal pipes either, so long as they are bonded etc.
But, don't forget, with cross-bonding you are not actually introducing earth potentials - you are just connecting the bits of metal together so they have the same potential. Unless one of these is also main bonded (not the case here) you are not actually earthing them.
But none-the-less, this is interesting. Is this in the Guidance Notes?. I believe there was a recent version of number 5. Is it in there? The nearest to this I have seen is in the paper by Paul Cook "Earthing plastic pipes", but that carries the disclaimer that the IEE is not responsible for the contents of the paper, so I would be reluctant to rely on *just* that. Don't recall seeing anything on this in the regs themselves, although they may have been relaxed without my noticing. It will certainly simplify things a lot.... Does it only apply to upstairs / without solid floors etc.?
That is the latest Guidance Notes yes? I would like to take a look and figure out where they are now coming from. As I say, some of the bonding stuff gets silly, and any detailed official guidance is welcome.
Nor me. That is what I meant when I said it gets silly. Connect the shower curtain rail to the towel rails to the radiator? Clearly absurd and useless.
alternatively
Good excuse to get out of the job. "Ooooh. I'll have to take the floor up or I'll be breaking the law. Just can't be done luv !" ;-)
The correct approach, whatever the regs imply. Pipes is one thing, metal fittings going nowhere another.
Only if you are taking the rules literally. Not a good idea these days.
Structural metalwork usually requires main bonding. Hence, it (and anything attached to it) also requires supplementary bonding in special locations.
Christian.
The bonding stuff *does* get silly: and it's not actually "official". The UK's approach to wiring standards is relatively sensible: the Regs themselves don't spell out totally detailed how-to-do-it requirements usually, but relatively general principles - "provide means for disconnection", "avoid overloads", and so on; and where there are more specific requirements, it's often qualified with "this is *a* way to achieve the requirements of Reg xxx-nn-mm, other ways may be appropriate to a particular installation". This approach cuts both ways: not only is a competent designer allowed to find a safe alternative way of complying, but merely following some detailed tabulated or "generally accepted" way of doing things does not discharge design responsibility (e.g. you can't apply the "standard" diversity, floor-area, and similar guidance if you know or should have known that the characteristics of the actual load in a given installation don't match the assumptions of the "standard" guidance).
This approach - as opposed to the slavish following of Code in the US and some European countries - is generally a Good Thing. But the need for interpretation and good sense does allow myths to spring up lower down the implementation chain; and this has certainly happened with earth bonding - with Trevor Marks' otherwise-reliable book being one of the culprits in the "festoon everything with green-n-yellow-wire" movement, which then becomes accepted practice among the peaked cap brigade...
Stefek
It used to be linked from the "Wiring Regulations" section of the IEE website, but I can't seem to find it now. However, the original link location works at:
Usually, though, the reason for bonding it is basically that it is already earthy, or subject to fault conditions that could make surfaces live. This would include metal pipework (main bonded elsewhere with possiblity of live wire chafing) or electrical appliances (bonded through CPC, live available). Therefore, in 95% of cases, supplementary bonding leads to a low impedence earth.
It was that article, but there wasn't any disclaimers on it when I read it, even though they have now magically appeared! In any case, the safety claims made in the article are compelling and I see no reason not to follow the advice contained. My only concern was with bath salts and having metal drainage, which wasn't addressed.
Christian.
In my fairly large first floor bathroom with a suspended wood floor I have a cast iron bath, toilet, bidet, wash hand basin. All water pipes copper - no plastic anywhere. And bonded in the cellar. I've also got a metal shower in a separate cubical - which IIRC has plastic input elbows, the central heating boiler in its own cupboard, the hot water storage tank, pump and valves etc in another, and one rad. Should all these pipes be cross bonded within the bathroom? If so I'll be paying for TLC's Xmas party...
Unfortunately, I'd say it is the official text on bonding which appears to get us in trouble. On main bonding, unless it has changed recently, the requirement for lightning conductors to require bonding comes direct from the regs. Likewise, the implication that anything metal in a bathroom should be bonded arises from the all-encompassing regs definition of "Extraneous-metal-part" and from the regulation on what does not need bonding.
Quite agree with you, the "this is the goal, find a way of achieving it" is by far the best. It is a shame that the regs couldn't find a way of laying down a requirement for bonding in this way, rather than the blind approach taken - on the lines of "if it is metal, wire it". Most of the parts of 7671 which have been in there for a long time still take the old approach you describe, but the sections on bonding seem to be prescriptive rather than goal-oriented. I wonder if this is part of the deskilling trend, as I find the same thing elsewhere; a more prescriptive approach in the more recent building regs than was the case with the earlier ones. Once upon a time, Part A was a case of "this table shows you how you can achieve the goal of xyz", but more recent parts are more detailed and constrained.
I can't say that I have seen much in Marks' book that goes further than the regs, although I only have an older edition of it - because on the whole I don't trust secondary sources. I prefer to see the original regs and interpret them. In fact, in his defence Marks does discuss why metal window's shouldn't be bonded, something I don't think you would see in the primary source (well, I don't recall seeing it)
Technically, for a lot of it the answer is probably yes.
Fortunately clamps and wire are cheap. Time isn't. Besides they keep changing the rules (e.g. bathroom zones have affected the detail of the bonding requirements w.r.t. CPCs). With all that lot you might want to wait until it looks likely it won't change again for a while!
Perhaps that is because of the claims from all the families of electrocuted bathers? ;-)
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