TNCS bonding for additions and alterations

[Deleted member 9648]

Was reading the spring 'Connections' mag today. In the 'questions' section the query was is it ok to carry out an alteration or addition to a TNCS install if the bonding is in 6.0mm and not practical to upgrade.
The answer was a definite no, it must be upgraded to 10.0mm. The article even suggested a way round this would be to convert to TT! Of course in the vast majority of situations we would all upgrade....
But I always thought the guidance on this was that if it really is not practical to upgrade, that if the 6.0mm has been in place for some time,and there is no sign of thermal or other damage, then a competent and qualified person can make the decision that the existing bonding is adequate.
Now I have not upgraded on very few occasions, but took our NICEIC assessor to a DB change where the 6.0mm remained in place on his last visit,and he was quite happy that there was good reason to leave it in place.
Another scenario may be with perfectly fine 6.0mm bonding in place...and just an additional socket to be added. That is hardly going to affect existing bonding arrangements or change anything.
'No madam, the bonding has been absolutely fine for 20 years,but because of that new socket you want You'll have to spend £200 putting a slightly bigger bonding wire in, but first you'll have to take up all that oak flooring you've just had laid on the landing, that OK?'
Has something changed or is that Connections article boll****?

 

[stevethesparks]

And when the customer has been put off by what they may deem unnecessary work, and decline for any such works to be done, they will be perfectly safe keeping their 3036 wooden consumers unit with 6mm main bonding conductors, as there is no obligation to upgrade.

 

[Deleted member 9648]

The requirement for minimum 10mm on a TNCS system is obviously for a very good reason, because main bonding may create a parallel path through which a significant neutral current may flow.

Common sense dictates that where a system has been in place for a considerable time with 6.0mm bonding, and is perfectly satisfactory without problems, then as long as an alteration or addition does not add a significant load then it will remain satisfactory. A DB change or adding another socket will not add a load and would not therefore increase any risk from 6.0mm bonding.
Adding a hefty shower....or a range cooker might well result in an increase in the risk of bonding carrying a current, so a responsible sparks would always upgrade accordingly.
I suspect this new guidance is part of the dumbing down of our industry. Because through no fault of their own those who have done the fast track courses do not have the knowledge to make those decisions, so the rest of us are not permitted to either .

 

[Welchyboy1]

And when the customer has been put off by what they may deem unnecessary work, and decline for any such works to be done, they will be perfectly safe keeping their 3036 wooden consumers unit with 6mm main bonding conductors, as there is no obligation to upgrade.

Its getting to the point of losing all my respect nowadays, AMD 3 consumer units was the last non-sense
and constantly changing just enough of the regs every few years to warrant a whole new update/regs books/courses blah blah
, watering down Part P just enough to keep every proffessional electrician coughing up every year to the schemes, but at the same time ensuring no-one steps on the toes of the big DIY outfits, by limiting their sales or am i being cynical?

 

[Wonderwall]

Does this thread not just prove, that the scenario of bonding water/ gas etc is extremely ambiguous throughout the electrical industry ?
I often come across the scenario where pipes are not bonded, and explain to the customer why I must carry this task out , and they always quite rightly, tell me they have stayed there for 40 years and had no problem. It's a minefield.
its makes us sparkies feel like we are creating work when all we are doing is try to confirm to the latest regs.
In my experience the test between any complete copper pipe pipe and an earth terminal is very low ohms. A fortitious earth no doubt.
I have never seen an earth clamp with charring on it. Ever . It should, if ever only carry some fault current, there is no serious load on it. If there is they have more serious problems surely.
Interested in other people's thoughts on this , as it's quite a bug bear of mine.
I have seen some installations where there is no earthing at all!! It has simply been disconnected or never been at all.
We then have to correct it, but it's not a one off scenario, I have seen it many times.

 

[Richard Burns]

Bonding is a critical part of the safety of an installation and if it is required to be used then it prevents a very serious risk of electric shock.
The problem is that the risk is presented only in very limited circumstances and if the system is working well and not TNCS then it will only be present for a very short time.
There are many installations where a fuse has never blown, if this is the case then the bonding has never come into play (if the cause of a fuse tripping were a fault to earth and not a short circuit).
Even if there have been a number of earth faults it could easily be that someone was not touching something metal and the faulty circuit at the same time for that 0.4s
In the case of a broken Neutral on TNCS then bonding would prevent dangerous voltages, but this is a rare event.
Similarly with earthing if there has not been an earth fault then there is no call for an earth, however if there is an earth fault then this would make the installation metalwork live indefinitely, partial protection only being provided by 30mA RCDs, if they are present.

The protective measures are there for a reason but unfortunately (or luckily) that reason may not arise often, but if it did arise then it would be dangerous.

One could similarly say that there is no need for MCBs because there has never been an over current or short circuit fault, however if it happens it would be a good thing if they were present!

Having said that I do find it does make you look a bit of a fool to a customer because they do not realise the reasoning behind the requirement, especially if it has never been an issue.

As an aside the testing of a copper pipe to an earth terminal will almost always give a low ohms reading as there will be interconnections from boilers or immersion heaters to the water / gas/ oil pipework, however this does not mean that the connection is suitable to carry fault current on a disconnected neutral or even the proportion of fault current that may flow on an earth fault.

 

[Deleted member 9648]

Does this thread not just prove, that the scenario of bonding water/ gas etc is extremely ambiguous throughout the electrical industry ?
I often come across the scenario where pipes are not bonded, and explain to the customer why I must carry this task out , and they always quite rightly, tell me they have stayed there for 40 years and had no problem. It's a minefield.
its makes us sparkies feel like we are creating work when all we are doing is try to confirm to the latest regs.
In my experience the test between any complete copper pipe pipe and an earth terminal is very low ohms. A fortitious earth no doubt.
I have never seen an earth clamp with charring on it. Ever . It should, if ever only carry some fault current, there is no serious load on it. If there is they have more serious problems surely.
Interested in other people's thoughts on this , as it's quite a bug bear of mine.
I have seen some installations where there is no earthing at all!! It has simply been disconnected or never been at all.
We then have to correct it, but it's not a one off scenario, I have seen it many times.

Not in the case of a TNCS system.
If you think about it the neutral is linked at the service head to a potential parallel path through bonded services which may well have a low resistance return path. Under load a very significant proportion of the neutral current may divert down that path.
I have never seen a bonding clamp with thermal damage either, and my argument is that a competent person should be able to make an assessment of the adequacy of undersized...(to present standards)...bonding which has nonetheless been satisfactory over many years.

 

[Midwest]

Common sense dictates that where a system has been in place for a considerable time with 6.0mm bonding, and is perfectly satisfactory without problems, then as long as an alteration or addition does not add a significant load then it will remain satisfactory.

I suspect this new guidance is part of the dumbing down of our industry. Because through no fault of their own those who have done the fast track courses do not have the knowledge to make those decisions, so the rest of us are not permitted to either .

In fairness wirepuller, I'm thinking THEY are actually agreeing with your statement.

The previous 'recommendation' was a carte blanche authorisation, for an electrician not to assess the condition of the installation. Now that decision has to be made locally by the electrician, involving knowledge and experience and a risk assessment process, and not some edict from a person sat in an office.
:thinking:

Of course there is another interpretation, in that their legal team have peered over their previous advice and seen that was not replicated anywhere in BS7671, which could make them responsible, should things go Pete Tong.

 

[Deleted member 9648]

In fairness wirepuller, I'm thinking THEY are actually agreeing with your statement.

The previous 'recommendation' was a carte blanche authorisation, for an electrician not to assess the condition of the installation. Now that decision has to be made locally by the electrician, involving knowledge and experience and a risk assessment process, and not some edict from a person sat in an office.
:thinking:

Of course there is another interpretation, in that their legal team have peered over their previous advice and seen that was not replicated anywhere in BS7671, which could make them responsible, should things go Pete Tong.

Good points....but the article seemed to make the case that if main bonding does not meet current requirements then no work should be carried out,no assessment etc....just no,full stop.

 

[Midwest]

Good points....but the article seemed to make the case that if main bonding does not meet current requirements then no work should be carried out,no assessment etc....just no,full stop.

The line given to me by Elecsa technical, was that it was the electrician to make that decision or risk assessment and that they weren't going to give everyone a get out of jail card, if you get my meaning.

 

[Pete999]

The line given to me by Elecsa technical, was that it was the electrician to make that decision or risk assessment and that they weren't going to give everyone a get out of jail card, if you get my meaning.

Some technical line that is then.

 

[Midwest]

Some technical line that is then.

Errgh?