gas installation pipe bonding [again]

It's just come back to me the very first words of the OP are from a song by my namesake a Scottish singer from the early 80s called Kelly Marie  think she was a bit of a one hit wonder

That`s the problem with "one size fits all" situation such as you bond ..... and you do not bond .......

In fact the "point of entry" thingy has a problem too!

An external meter then metalic pipe thru wall - on the outside just as it goes in = point of entry whilst on the inside just as it comes in = point of entry. Any  voltages to global earth or to installation earth is almost exactly the same as resistance/impedance is almost nil.

So, where is it most effective regards verifying, installing and remaining secure against disconnection by accident or by design (including bad intent) ?

Horses Courses.

In any event you got the "outside tap" scenario.

How often do I see an external meter box with a 10.0 G/Y clamped to an earth rod on old terraced (1900) houses to "bond" gas supply on TNS houses (treat as undeclared TNC-S anyway) ?

B.G. suggests that external electrical faults can be dangerous if protective bonding is not present inside an installation......

https://www.youtube.com/watch?v=hOoKI0G9KVI


Z.

Reference; electrically insulating inserts in gas pipes, a historical report...

https://electrical.theiet.org/wiring-matters/years/2016/61-summer-2016/insulation-inserts-in-metallic-gas-service-pipes-to-consumers-premises/


Note. 

To summarise, the two main reasons for insulating inserts/insulation joints in metallic pipework are to prevent corrosion and to prevent pipes being used as a path for fault current. Also, the main protective bonding requirements in BS 7671:2008+A3:2015 are understood to be written on the expectation that insulating inserts /insulation joints are installed in metallic service pipework.

It is important to be aware that this article only gives a brief overview of the issue of insulation inserts. 

Z.

411.3.1.2 says, regarding main protective bonding,  "IN EACH INSTALLATION"..... so we are not concerned with anything OUTSIDE the installation are we.

But inside and outside the electrical installation isn't the same a inside and outside the building - as the electrical installation often extends outside (the building)  these days.

 

It's worse than odd.


It both defeats the purpose of the bonding rendering it useless and leaving the extraneous-conductive-part not bonded, and 


the insulating section makes the consumer's pipework NOT an extraneous-conductive-part which therefore does not requiring bonding.

I'm not quite so pessimistic. If there's no IJ then then bonding works perfectly well.


If there is an IJ then either the consumer pipework is still extraneous (e.g. as it picks up an Earth potential from within the installation) so the bonding remains required (and effective) or it isn't extraneous in which case the bonding is wasted but likely does no harm (as it'll likely be connected to the MET via boiler or hob c.p.c.s anyway). At least we don't have to contend with the issue of push-fit plastic joints being retrofitted willy nilly on internal gas pipes.


Yes there is the issue that the short length of gas supply pipe before the IJ isn't bonded - and perhaps ideally it could be shrouded in insulating material to reduce the shock risk. But as we can't really tell if an IJ has been fitted - or just as importantly whether one will be fitted at a later date - bonding to the consumer's side seems like a reasonable (if far from ideal) compromise.


This particular problem will likely disappear anyway as the final few remaining steel gas service pipes get replaced by plastic, and then North Sea gas runs out.


    - Andy.

Now then, a bit more detail - sorry, its wordy but I've tried to be brief.  This is a bungalow affair btw (with not habitable/used roof spaces).


The only apparant MEB is as previouslly noted, on a copper riser to the central heating radiator and fed through internal wall to the MET.   There have been previous extensive works with plumbing.


Installation pipe to boiler parts:


The gas service service pipe is still presumed to be metal at this stage and comes out of ground into the meter cupboard mounted externally.  The bare copper customer installation pipe comes out of meter, then out of bottom of the meter cupboard, then loops up and around the house, still externally and for the ~12m, where it goes into the house through the wall. Once inside, it is inaccessible being enclosed in a wooden boxing for a short section going into the roof space. It comes out of the roof space a small run later and immediately down to the boiler in a short straight run.  None of this is or has been MEB'd for some reason, despite previous works.


Reasonably, the only section of that pipe that is readily accessible *internally* is it the ~80cm straight run down from the ceiling into the boiler casing (and its subsequent inlet connection to the boiler). Only half of that 80cm run, from the ceiling, is touchable metal and the rest down to the boiler appears shrouded in a plastic pipe until just into the boiler casing at the back. Even the touchable part cant be reached without ladder/steps etc.


From underneath the boiler, the internal installation pipes (central heating and hot water) leave the boiler (hot water goes via a sink tap) in copper surface-mounted for a few metres and then all go into plastic pipes, which then run into a floor void to not be seen again rising. The cold water feed to the boiler (going via the sink tap) in copper for the last few metres up to the boiler, is also coming out of the floor void having been delivered to that point via plastic pipe (see later comment *).


Question: based on the above, would any of the above,  up to the plastic pipework joints  need MEB  ?   My tentative thoughts, yes; because for external electricity network faults only (unless the boiler CPC could introduce installation faults), all the copper piping up to and leaving the boiler would be affected due to the the extranous copper pipe from the gas meter and its [presumed metal] service pipe.  I give way to be corrected/debated/enhanced.


Question: where would one bond that part?    The only 'as it enters first habitable space', is the short length unsleaved section at the ceiling level above the boiler. This point is much further away from the MET, than the gas engineer suggested point of bonding at the  customer installation pipe at the gas meter.  Either bond point will still 'liven' up the external pipe route, so it really is a just a matter of  whether the 'at point of entry' is critical re: accidental removal of the bonding/branching probs. For this case in question, I doubt it matters overly.   Again I give way to be corrected/debated/enhanced.


Downstream (after plastic sections) central heating parts:


Now then, what happens after the plastic pipe conversions mentioned above and why is there a MEB (or was/is it an additional bond before the internal plastic pipe works !) from the central heating pipe work to the MET by the consumer unit.


Well as mentioned at the outset, it would appear that despite the plastic piping upstream, seemingly the rest of the central heating pipe work is still all in copper and appears to be introducing an earth potential - running on/in the ground soil under the floors, damp conditions, or some other reason.   That may explain why the previous electricians  had this rad-to-MET bond in place.


I'm told there has been a lot of previous work done at this place, new boiler, new plastic pipe works (new bathroom) and possible new consumer unit...but no paper work to be seen.  What stops a plumber coming along and  banging in plastic here and there and not realise about bonding implications: "hey look, I'm going to use plastic for this bit, but you may need an electrician to come in to check the bonding is still ok when I'm finished"  :)    Or may be, any previous electrical works have not check bonding was up to scratch.  Who knows.  ho hum.


* (further note from earlier).


The water supply to the property comes in under the wooden floor of a long hall. There is  a small access hatch (well, lifting some cut floor boards would be more accurate) in the floor under the main door footwell, to access the stop cock (its actually quite hard to get to !) .  The pipe runs under the floor, inaccessible (excepting the hatch access), until it appears to be  interrupted by a plastic joint insert and a little further is converted into the plastic pipe as mentioned earlier.  Its hard to see it all unfortunately.


Question: does this need bonding ?   My thoughts, if reaching down to the stop cock (one has to lay on the wooden [and carpeted] floor!) and not being able to simultaneously touch any other parts, then no; because  its not accessible other than that and whats the risk; additionally it turns into plastic before any other usage point. Again I give way to correction etc.



Summary:


I feel that a MEB bond on the main incoming gas pipe is needed  (subject to confirmation assessment/clarification) for the boiler and other co-located copper extraneous copper pipe parts (where to do that is a matter of choice).   The MEB (or additional bonding ) that is still present internally at the central heating pipe downstream should be retained as for whatever reason, testing (< 25kOhms) shows it is still 'earthy'.


Regards and sorry to swallow up so much space etc.  Thank you for the previous comments. etc.  Apolgoes for grammar and spelling.   Any comments to any of the above greatfully received.

The bond to the rads may well be just that the radiators were not really earthed and for supplementary bonding rather than main.

After all there is nothing in the regs that stops you earthing things that do not need it, and a lot of folk from the era of the 15th edition (supplementary bonding  in kitchens) still feel better to err on the side of 'earth everything'  without thinking too deeply- I suspect it is left over from some previous work, and it does no harm, just confuses.

I think your logic is correct, you only really need to guard against credible fault conditions.

And yes, you will have PME earth on the pipe outdoors, but to put that risk into perpective there are many bus shelters and lamp-posts with PME mains supply up and down the land, and there are no early morning teams required to remove the electrocuted bodies from beside them, so it is an accepted small risk. It is not like the car, boat or caravan situation that is fed by flex, and folk will repeatedly grab the handles while in good contact with terra-firma.

Regs wise it is going to be hard to satisfy everyone.

Actually assuming the boiler CPC is in good shape, you probably already do have mains earth voltage outside, just not in a clearly visible and easily inspected sort of way.

I'd be tempted to put a bond in a place for water and gas that is easy to do and available to inspect, and then worry no further. If it is connecting to something that by dint of an IJ or plastic pipe underground did not strictly need it, no one will be surprised or upset.