Should I ever be confronted with bonding the lightning protective systems case, I might give consideration to rejecting it. However, on the central heating pipes issue and most of the others, the case for is very similar to that for gas/water. They are all extraneous metal parts.
On the telecomms side he does say that it requires the permission of the owner/operator which I doubt would be forthcoming. However, from the
*purely* electrical safety point of view (as opposed to concerns about how you affect the telco equipment etc. ) it is consistent with the general approach of bonding extraneous metal parts.On the lightning point, as I said in an earlier post, I don't really see where the need would arise anyway - but it *is* what the IEE Regs/OSG etc, etc. say, as well as Trevor Marks. As for whether it should be removed, I don't feel qualified enough to say for sure.
Ah! I don't have any problem with the possibility that the standards **may** be wrong. Indeed, I understand there were bits introduced into the 15th edition that were taken out in the 16th because they were no longer believed to reflect best practice. But, my problem is that I don't know the subject area in enough detail to overturn the IEE view; nor do I have the time to get to the point where I do. And if I am going to second guess a committee of individuals brought together to produce the standard I am going to have to be pretty expert in arguments for and against. My other problem is that 7671 has a certain quasi-legal force. Deviating from it and then trying to argue that it is wrong when you are being sued/prosecuted won't get you far.
Sure, errors occur in papers. But for the error to have reached British Standard status and to have gone unchallenged for over 12 years (a period in which loads of amendments have been published) is not likely. They obviously believe this is best practice.
Well, why don't you stir up the IEEE to put the case to the IEE about how some clauses in the regs are liable to result in damage to electronic equipment? I.e. get the IEEE to start representing the interests of *its* members in the standards process. You can't blame the IEE for putting this stuff in if nobody with a different perspective puts the other side.
Interesting..... I think the answer is that in your case, with lightning, the impedance requirements are a lot tougher.
The main purpose of equipotential bonding is to reduce the touch voltages appearing between the exposed conductive parts (e.g. the appliance case) and the extraneous conductive parts (e.g the pipework) during a fault condition within the appliance which results in its exposed parts becoming live.
If the extraneous parts (pipes) are well bonded, then that touch voltage will be largely determined by the impedance between case and the earth bar: i.e. that of the CPC (the appliance earth wire in old money).
So, reducing the impedance of the equipotential bond beyond a certain point is pointless. In fact, it would be better if the equipotential bond of whatever is touched had the same impedance as the CPC of the faulty appliance - in which case no voltage difference would be present. But of course that is impossible to arrange.
In normal environments, I would expect the sort of impedances that get inserted into the circuit as a result of corrosion etc. to be quite small. On the other hand, I would imagine that lightning strike currents passing through even a one milliohm bond could do a lot of damage.
But your point applies more generally to the CPC. In a ring circuit, you generally have it looping in and out of socket after socket, joined only by repeated mechanical joins. Does the collective impedance of these rise measurably over the years, or does the rigid contact of metal on metal prevent oxidation of the contact surfaces? I have never actually re-measured an installation and compared the results with the original figures, so I can't comment. Howeve, except in damp conditions, I would be surprised if they did appreciable affect the impedance - at least enough to affect the automatic disconnection times. But that is not based on any hard evidence.
I bonded my central heating pipes in the cellar - along with all the other services. There's no plastic pipes anywhere. Does this cover it?
"Mike" wrote | Partially because it is unsightly but primarily because it is | this 'gold-plating' of regulations that is driving costs higher | and higher. | Before you know it BCOs are demanding these clips even though | they are superfluous to all known reasons. Six clips costs | about £2 but the cost of fitting them is much higher, even | for a DIYer if you cost your time.
And more than that if you have two combi boilers.
Owain
I'd say that would be fine. I once did a flat of mine under the floorboards so the cables were not visible (which could be a problem if it is ever inspected). The only thing to note is that it is preferable to bond it to the main pipes, rather than on a branch. But as long as it is done somewhere and in an unbroken length of the proper gauge wire then you are covered.
Yes - I bonded both the flow and return for the ground floor - both 22mm. All the basic pipework connectors are solder types - only compression ones used at the rads, etc.
Agreed - it is NEVER bonded at the terminal (user) end. To do so could mean a lightning strike to your incorrectly bonded lightning rod, or just to the overhead mains cable feeding your house, taking out a whole central office.
You've hit the nail on the real problem. Until Jan 1st I can quite legally argue that my way is better and provided I can convince an independent third party chartered engineer of this I can do as I wish. But with Part P this becomes a whole different issue. However if a BCO tells me to bond boiler pipes on one of my developments then this may well be heading to court.
The IEEE is an US led 'worldwide' body who issue a set of regs based on 110v mains. If they were allowed to enter the fray they would argue for this to be adopted worldwide, probably not the discussion needed here.
The point of contact is, however, not subject to corrosion. If you remove the pipe clamps you will see a shiny mark there.
This part of the regs does seem to be observed in the breach quite a bit.
Whilst it is common to see the correct earth wire(s) for gas and water depart from the consumer unit or earth block. It is rare to see one installed for the central heating. I was falsely under the impression that this was performed at the boiler. However in practice the gas supply pipe is going to be a good earth, [1] so bonding all the pipework there will effectively bring the heating pipework into the equipotential frame.
[1] It is just possible that screwed joints with PTFE tape might not be electrically sound. However invariably screwed joint sare on older work which may well have been installed prior to the development of PTFE tape.
Any time I've dismantled a PTFE wrapped thread, the PTFE tape has been in shreds. Which means the threads are making metal to metal contact. Its purpose is to fill the gaps in a poorly machined thread - precision threads wouldn't leak.
If the reaction on here was anything to go by, I imagine that is because few people know about it. In most installations it won't make a jot of difference except when inspected. Besides, I have seen it done with straps attached to painted pipes. Which is nice and effective.
Yes, could well be. Also, the bonding is put there to reduce the effects of static around the fuel lines.
snip
So would I! And I have seen the results.
Many thanks for you input
Dave
On Sat, 11 Dec 2004 22:27:01 -0000, "Mike" strung together this:
For the same reason that exposed metalwork such as a buildings structure needs bonding.
I don't think a boiler (without electrical supply) can be classified as part of the building strucutre. If this was the case then all radiators with plastic pipes would need clamps which I think we all agreed some months ago was not the case.
Things like fire escapes and balcony railings are outside the equipotential zone so they don't have to. Exposed internal structural metalwork is rare because of the fire resistance part of B-regs.
Supplementary bonding is not required for lengths of less than 0.5m. Presumably where a CH system has little or no copper pipe it would be exempt?
Metal steps set in plastic sides are all the rage currently. I don't see each step being earthed.
Most radiators are say 1m wide, plus the valves and often a metal downpipe to under the floor before they get to the plastic. Are you saying they should be bonded ?
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