Sorry for this but my boiler recently had her annual service all was well except they said I don't have any bonding in place except I think I do the gas main is bonded in the meter cupboard and the radiators and hot and cold water feeds are all bonded in the bathroom upstairs. All pipework is copper throughout the plumbing never been altered in 40 years except for a new boiler oh and removal of the water tanks. So can I be confident the bonding upstairs is good enough?
Geoff - I am struggling to see your point here.
JP - Yes I agree.
Both these statements are made only with reference to our regs - the wiring regs.
I have no idea what the gasregs actually say.
If they both say exactly the same thing then great, if not we have a problem.
If you are an electrician then work to the electrical regs but if you are part of the gas industry then work to the gas regs - does not seem a good idea unless you can comply with both regs with no conflict.
Kelly - it used to be pretty clear - if it presents as TNS then it is TNS unless you see a PME sticker on it.
That was years ago.
Nowadays it might have been TNS originally but a nearby repair of the service cable makes it behave so very like TNC-S that we should treat it as if it is actually PME but without the PME notice on it unless the supplier confirms it is actually TNS.
From reading all of the above I see that there is still significant confusion about main bonding. Geoff would like to bond to incoming metal pipes even if there is an insulating section before the consumer pipework, presumably to prevent shocks across the insulating section. This misses the point of the main bonding completely, which is to prevent extraneous voltages from being brought into a property. The complexity comes because back in the days of metal distribution pipework, a potential from another property could arrive at your property. The insulated sections are intended to prevent this, without the risk of large currents flowing in the bonding, in fact meaning that virtually none can. In a PME system (and it all is now) we have a new risk because neutral and Earth are a single conductor. If this breaks and becomes an open circuit, very large currents (several hundred amps) can easily flow in an external pipe between properties. This is liable to melt said pipe, which is a bad outcome. It is also likely to melt a bonding conductor and distribution cables. The best solution is therefore to remove the main bonding with the insulating sections. This is not about ensuring that external pipework cannot be a shock source (which if you think about it is very unlikely, not many of us hang onto both sides of the insulated link, even when reading the gas meter) but preventing external damage that could be serious causing gas or water leaks, or electrical failures. Inside the property, normal earthing keeps all exposed conductive parts at more or less the same potential under fault conditions, and it matters not if the pipework is many isolated sections.
Inside a property with normal earthing, main bonding effectively does nothing useful and is a significant potential problem. With TN-S the use is debatable, does it really matter if a confined space has extraneous parts above normal Earth potential, the same potential as all the exposed conductive parts, probably not? Therefore insulating sections are better than main bonding, although it takes some considerable thought to change attitude to main bonding. Plumbers are very unlikely to make this change!
Tomgunn:
Sorry to intrude BUT… why was ‘cross bonding’, (something I always used to do, in the past), stopped, (introducing a ‘potential’ where it didn't exist)?
Thanks / regards… Tom
It never went away. Just not always necessary in domestic installs.
Certainly used regularly in major infrastructure, absolutely required for EMC purposes (Section 444 of BS 7671) - we call it “common bonding network” (CBN) instead of “cross bonding”.
gkenyon:
Tomgunn:
Sorry to intrude BUT… why was ‘cross bonding’, (something I always used to do, in the past), stopped, (introducing a ‘potential’ where it didn't exist)?
Thanks / regards… Tom
It never went away. Just not always necessary in domestic installs.
Certainly used regularly in major infrastructure, absolutely required for EMC purposes (Section 444 of BS 7671) - we call it “common bonding network” (CBN) instead of “cross bonding”.
Hi, thanks for the update!!
Sounds a bit like our football leagues? Like we all know that the ‘Premier League’ is still the 1st / 2nd divisions etc… so, it's now known as the ‘CBN?'
Many thanks for this!!
regards… Tom
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