Earth Bonding

[westie101]

Er so we have an LPG system that requires bonding yet an oil system doesn't as it may or may not be in contact with earth potential!

And surely the oil pipe connects to a boiler which will in all probability use electricity in it's operation, in which case there will be a connection to the MET via the wiring!

Unless of course there is an insulated section in the oil pipe which might remove the need to bond it!

 

[Electrifying]

Er so we have an LPG system that requires bonding yet an oil system doesn't as it may or may not be in contact with earth potential!

And surely the oil pipe connects to a boiler which will in all probability use electricity in it's operation, in which case there will be a connection to the MET via the wiring!

Unless of course there is an insulated section in the oil pipe which might remove the need to bond it!

This is probably the most sensible suggestion.

 

[EFLImpudence]

This is an interesting point. When I had some gas work done here a few months ago, checking the Main Bonding of the gas supply was certainly something that was done as part of the paperwork/certification of the gas work.

Good point.

I recently attended a Gas Safety Check and whilst on the certificate "Is Equipotential Bonding satisfactory" is ticked "Yes" the engineer definitely did not measure anything. He presumably may have just seen it.

 

[JohnW2]

And you might reconsider when, under a fault condition that, for whatever reason, doesn't clear, the installation metalwork and any metalwork bonded to it, rises to 230V. This would take the oil-tank, which is outside, to 230V. The man coming to fill said oil-tank, standing on true earth, would not be impressed......especially if he's dead. You see, 'unneccesary bonding' can do harm.

All true, but there's not much one can do about it (even with an earth rod - see below). The reason why 'unnecessary bonding' in a situation like this cannot usually 'do any harm' is that, as I wrote to EFLI, the pipework in question is almost inevitably implicitly 'bonded' via its mechanical connections to (bonded) water pipes. So, yes, an uncleared fault could result in the tank potential rising to nearly 230V above that of the truth earth below - whether or not one had installed something called a 'bonding conductor'.

The pipe coming into the house from the oil tank is not part of the electrical installation - so it's not an Exposed Conductive Part and doesn't require earthing.

Agreed.

The pipe is also not an Extraneous Conductive Part - this could be tested and proven - so it doesn't require bonding.

That's what the discussion with EFLI is about. Test it during a period of high rainfall and I'm not convinced you'd necessarily be right - let's face it, we've had people here talking about bonding of damp internal walls not so long ago!

If you really wanted to 'bond' the pipe to the MET, then you should first sink an earth rod and earth the tank - that way, if the tank were to go 'live' due to your 'bonding', there would be minimal risk to the operative filling the tank. Thoughts???

I've seen that done, but I'm not sure that it would give me all that much reassurance. Given the resistance of the earth rod compared with the R1+R2 of the fault path, the potential of the electrode will rise to nearly full supply potential relative to true earth in the case of an uncleared fault. The oil delivery man would only be spared if the potential of the actual earth on which he was standing also rose to a similar potential - but that is subject to so many variables that I would not want to be the one to try it out! ... of course, if one did earth the tank in that way, then one would have no choice but to main bond the pipe, which then would definitely have become an extraneous-conductive-part!

Kind Regards, John

 

[JohnW2]

Er so we have an LPG system that requires bonding yet an oil system doesn't as it may or may not be in contact with earth potential!

Indeed - but, to be fair, my LPG supply definitely does need bonding because, although most of the buried supply pipe is plastic, the last metre or so of buried pipe is metal.

Er And surely the oil pipe connects to a boiler which will in all probability use electricity in it's operation, in which case there will be a connection to the MET via the wiring!

Exactly - and,as I've been saying, even more to the point the oil pipe will almost certainly be connected via the bolier metalwork to water pipes which themselves will almost certainly be bonded to the MET.

Kind Regards, John.

 

[fidom]

Sorry about the diversions - we're like that.


The Gas Safety Check is mandatory but you do not have to legally have the electrical installation checked to let your house (unless it is to be a house of multiple occupancy - several independent lets, like students)



Have a good look at where the pipes run and see if you can see any green/yellow cable.
Why not take some pictures of the gas meter and water entry and post them on here

Perhaps I should explain more about the setup. The only gas pipe is in the workshop. When I moved in here there was a gas meter but no gas appliances. I put in the gas boiler in the same building and had a Corgi engineer come to plumb in the gas supply and commission the boiler. I did the earth bonding to the gas meter, the gas pipe and each of the water pipes to the boiler. I used 10mm green and yellow cable with proper BS951 clamps and ran this to the CU. There were already earth bonding cables from the water pipes in the kitchen and the metal bath to the CU. Most of the kitchen and bathroom pipework is hidden but access to the bonding cables / clamps is available in the washing machine space and behind the bath panel. I could have shown the electricians these locations but they didn't ask, they must have just assumed there was no bonding.

 

[holmslaw]

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