Neat method for main bonding to exit wall

[Donkmeister]

I'm replacing my old kitchen as part of my house refurb.

I need to replace the protective bonding to the incoming water main and fit protective bonding to my gas incomer. The gas supply has no protective bond (it is plastic up to my boundary, then steel pipe underground for the ~50 feet to the meter, testing it there is no continuity between the electrical earth and the pipework), and the water supply is bonded with a 4mm single that is just dangling down a wall... undersized and unsightly!

I have a 16mm main earth (TN-S system) and I intend to fit 10mm bonding conductors to water and gas. Ordinarily I see bonding just emerging from the plaster where it is needed, but I was wondering if there is a neater way? Perhaps using a flex outlet plate?

Also, is it best practice to use a crimped lug on the end of the bonding conductor or is it fine to put the wire into the screw clamp?

(Appreciating that this work is notifiable, it is being carried out under a Building Notice and I have already had the first stage of my rewire inspected and certified by the BCO's contractor.)

 

[EFLImpudence]

The gas supply has no protective bond (it is plastic up to my boundary, then steel pipe underground for the ~50 feet to the meter, testing it there is no continuity between the electrical earth and the pipework),

If that is true then no bonding is required.

I have a 16mm main earth (TN-S system) and I intend to fit 10mm bonding conductors to water and gas. Ordinarily I see bonding just emerging from the plaster where it is needed, but I was wondering if there is a neater way? Perhaps using a flex outlet plate?

You can use whatever you like but I would advise that you do not cut the conductor; just have it passing through whatever you decide to use.

Also, is it best practice to use a crimped lug on the end of the bonding conductor or is it fine to put the wire into the screw clamp?

Properly (not cheap squash flat rubbish) crimped lugs might be better but either is acceptable.

(Appreciating that this work is notifiable, it is being carried out under a Building Notice and I have already had the first stage of my rewire inspected and certified by the BCO's contractor.)

Fitting bonding conductors is not notifiable.

 

[aptsys]

and the water supply is bonded with a 4mm single that is just dangling down a wall... undersized and unsightly!

Is it undersized on a TN-S supply? Have you done the calcs?

 

[JohnW2]

If that is true then no bonding is required.

If it were true, then you would obviously be right. However, can you believe** that 50 feet of underground steel pipe does not have an appreciable path to earth? I suspect that the "no continuity" reported by the OP might be the results of a measurement with a low-resistance, low-voltage, device.

** the other possibility is that the steel pipe is currently plastic-coated, such that the pipe really does not (currently) provide an appreciable path to earth. If that were the case, and if it were me, I don't think I would want to trust that underground insulation to remain intact for ever, so would be very inclined to bond the pipe.

Kind Regards, John

 

[EFLImpudence]

I was going to qualify it but it is either true or it is not.

There could be an insulating section.

 

[conny]

My son in law has an oil fired boiler. The feed pipe appeared to be plastic and disappeared into the ground by the tank before re-emerging against the house wall but had been bonded at the tank end.
On closer inspection the feed pipe is actually copper with a thick sleeving over it. The electrician had cut a nice neat section of the sleeving out to enable a proper earth clamp to be fitted.

 

[JohnW2]

I was going to qualify it but it is either true or it is not.

As I've said before, whether a pipe (or whatever) has appreciable "continuity" to earth is, indeed, "either true or not" at a particular point in time (i.e. when a measurement is taken), but I have suggested that one should consider possible changes in the future ...

... my LPG pipe runs in plastic for 40-50 metres underground in plastic from the tank to my house. Just outside my house, it changes into (bare, galvanised) steel which rises about 600mm through what is primarily gravel (with some soil/sand at the bottom), and then enters my house (as metal). I can't actually try it, but if I disconnected the incoming pipe from the incidental earthing (boiler etc.), then, under very dry conditions (like last summer) I feel sure that the measured resistance from that pipe to earth would be extremely high - certainly high enough to not require bonding (at that point in time). However, after a good downpour it seems very probable that the resistance would then be low enough to require bonding. For that reason, I would not rely on a measurement taken during very dry conditions as a basis for deciding whether or not bonding was required.

So, similarly, I would personally be inclined to take the same approach with an underground plastic-coated metal pipe. Even if (as would be probable), the resistance to earth when measured with the coating intact was plenty high enough to not require bonding, I probably would not want to rely on that coating remaining intact.

There could be an insulating section.

Yes, there could be. However, if one has not seen it, or seen authoritative documentation of its existence, one can't assume that such is present.

Kind Regards, John

 

[Donkmeister]

Is it undersized on a TN-S supply? Have you done the calcs?

I'm looking at para 544 of my regs book and it looks like absolute rules to me - a series of shalls, a criterion for minimum CSA and a look-up table...

I must be missing something here... what calcs should I be doing?

 

[EFLImpudence]

Lots

Yes, but it is a bit pointless detailing every single possibility with a view to discreditting my reply.
You may of course explain all the principles and options to the OP.

You will note that my statement began with "IF".

 

[EFLImpudence]

I'm looking at para 544 of my regs book and it looks like absolute rules to me - a series of shalls, a criterion for minimum CSA and a look-up table...

Yes, but those shalls only apply to parts that are Extraneous-conductive-parts.

I must be missing something here... what calcs should I be doing?

The calcs in 543.1.3 for sizing main bonding conductors. TN-S requires very small.

However, you must be certain it still is TN-S. Lots today have been converted to TN-C-S by cheapskate suppliers.

 

[JohnW2]

Yes, but it is a bit pointless detailing every single possibility with a view to discreditting my reply.

Hey, you surely know that that's not my style or personality. I was not trying to 'discredit' your reply - I was merely qualifying it.

My concern was that we don't even know how the OP determined that there was 'no continuity' to earth. Despite the 'IF', he may well have concluded from what was being said that if he felt that he had 'established no continuity' (by whatever means), that meant that bonding would not be required.

Kind Regards, John

 

[ban-all-sheds]

And let's not forget that "there is no continuity between the electrical earth and the pipework" might mean that the installation has no earth, not that the pipe is not an E-C-P.

 

[JohnW2]

And let's not forget that "there is no continuity between the electrical earth and the pipework" might mean that the installation has no earth, not that the pipe is not an E-C-P.

True - and that's one of the reasons why one has to be careful if using 'resistance to MET' as a determinant of whether or not something is an extraneous-c-p. One really should not undertake such a test unless one has first established that there is an 'effective earth' connected to the MET.

Kind Regards, John