To bond or not to bond..?

[flyingsparks]

Oil line comes in to house through wall to aga. Then clipped along external wall to plastic oil tank sat up off ground. At no point does the pipe go near the ground. PVC coated pipe all the way.

I can't see it needs bonding no way it could introduce a potential?

 

[Lectrician]

No. No need, although the NIC would recommend it is, they would not pull you up for not doing so.

If it was a tidy 30 min job, I would likely do it.

 

[securespark]

I wonder how they justify making up their own rules?

 

[ericmark]

I think we need to go back to basics and ask why do we bond anything?

1) To prevent an unseen fault from causing danger. The standard lamp knocked over by dog hitting radiator making radiators in other room become live is the one quoted.

So with the oil pipe we want to stop a fault inside being transmitted outside or a fault outside from being transmitted inside.

So next question is bond to what?

Plastic tank so nothing there to bond to and indoors it is already bonded to Aga through the brass fittings.

So the question is should the Aga be bonded. Where it supplies hot water either potable of central heating then clearly it needs bonding to the house earth but in bonding you actually introduce a danger should the house earth not be the same as the garden earth then some one outside could get a shock touching the stop cock on the tank.

As we look at the risks therefore there are risks either way bond or not to bond so we tend to hide behind 411.3.1.2 and bond. If we class it as supplementary equipotential bonding then with a RCD protected house we could omit it, but if we just class it as equipotential bonding then we can't.

So however daft it may seem there is only one way we can be certain of the get of of jail card and that is to bond.

 

[EFLImpudence]

I think we need to go back to basics and ask why do we bond anything?

Indeed we do.

To prevent an unseen fault from causing danger. The standard lamp knocked over by dog hitting radiator making radiators in other room become live is the one quoted.

That is NOT the reason.
What if your lamp falls on a spoon?

So with the oil pipe we want to stop a fault inside being transmitted outside or a fault outside from being transmitted inside.

No, we want to prevent true earth (or other) potential being transmitted indoors.

Plastic tank so nothing there to bond to and indoors it is already bonded to Aga through the brass fittings.

Likely true.
If it does not require bonding then what happens indoors is irrelevant.

So the question is should the Aga be bonded.

Not unless it has contact with the ground.

Where it supplies hot water either potable of central heating then clearly it needs bonding to the house earth

Not unless it has contact with the ground.

but in bonding you actually introduce a danger should the house earth not be the same as the garden earth then some one outside could get a shock touching the stop cock on the tank.

Quite the opposite.
Edit - It depends whether the bonding was actually required or not.

As we look at the risks therefore there are risks either way bond or not to bond so we tend to hide behind 411.3.1.2 and bond.

If we do then we are wrong.

If we class it as supplementary equipotential bonding then with a RCD protected house we could omit it, but if we just class it as equipotential bonding then we can't.

Supplementary bonding is not required in a kitchen.

So however daft it may seem there is only one way we can be certain of the get of of jail card and that is to bond.

No.
There is only one way to determine whether to bond or not.
That is to determine whether the oil pipe or the Aga is an extraneous-conductive-part.

 

[bernardgreen]

Common sense means I have to agree with eric. The important part is " unseen fault.

Bonding the oil pipe to the internal "earth" can and has presented a hazard to someone outside the building when the internal "earth" is not at the some potential as the ground outside the building. I know a gas meter reader who wears gloves when touching gas meters. He would not be able to see i there was fault that had bought the internal "earth" potential to a dangerously high voltage. The gas meter would then present the risk of severe possibly fatal shock.

If a standard lamp fall onto a spoon and the spoon becomes live then one can see the fault and unplug the damaged lamp before picking up the spoon.

If the standard lamp falls onto a radiator in the lounge and makes it live that fault will not be seen by someone in a different room where the radiator is also live via un-bonded pipe work. Hence they are un-aware of the dangerous state of the radiator in the room they are in.

 

[EFLImpudence]

Common sense means I have to agree with eric. The important part is " unseen fault.

That's not common sense.

Bonding the oil pipe to the internal "earth" can and has presented a hazard to someone outside the building when the internal "earth" is not at the some potential as the ground outside the building.

Not if the pipe is extraneous.
If it is not extraneous then it is the same as an outside tap; other methods will need to be employed to remove this hazard.

I know a gas meter reader who wears gloves when touching gas meters. He would not be able to see in there was fault that had bought the internal "earth" potential to a dangerously high voltage. The gas meter would then present the risk of severe possibly fatal shock.

As above.

If a standard lamp fall onto a spoon and the spoon becomes live then one can see the fault and unplug the damaged lamp before picking up the spoon.

But the purpose of bonding is not to safeguard against parts becoming live.
If you feel this is a likelihood then you should earth everything and live with the consequences of the alternative.

If the standard lamp falls onto a radiator in the lounge and make it live that fault will not be seen by someone in a different room where the radiator is also live via un-bonded pipe work. Hence they are un-aware of the dangerous state of the radiator in the room they are in.

Nevertheless that is not a good reason for earthing non-extraneous-conductive-parts.


If you had a house where NONE of the internal pipework was extraneous it would be foolish to earth it. The same applies to a proportion of the pipework
Earthing is not a good thing; it is a necessary evil.

Much better would be to get rid of these unstable standard lamps.

 

[Jackrae]

Or get rid of dog and save the environment ?

 

[ericmark]

I can see the point between bonding and earthing where in the main to bond means to get all parts at the same voltage what every that voltage is but to earth means to bring to earth potential.

However in the real world they are very much linked together. With a house on a TT supply the RCD protection means in real terms should a fault in the house be transmitted to the garden then anyone getting a shock will cause the RCD to trip and limit the time they can get a shock for so if the isolation tap on the fuel tank is connected to house earth it will fail safe.

With a TN-C-S supply however the fault may not be in the house and while all items in the house are bonded together although the bonded voltage may vary from ground voltage like the bird on the wire no shock will be received.

However export that bonding outside where someone can be touching true earth and bonded metal work at the same time then just like the TT system they can get a shock. But unlike the TT system when the RCD operates the source of the voltage differential may not be removed. Hence there is a danger.

This danger means that where there is a lot of exposed metal work like with boats, caravans and petrol stations TN-C-S is banned.

 

[ericmark]

Question is TN-C-S earthing or bonding? As it does not always under fault conditions connect to true earth?

 

[JohnW2]

Common sense means I have to agree with eric. .... Bonding the oil pipe to the internal "earth" can and has presented a hazard to someone outside the building when the internal "earth" is not at the some potential as the ground outside the building. I know a gas meter reader who wears gloves when touching gas meters.

I'm a bit confused by the apparent contradiction here. Eric's view was, in essence, "if in doubt, bond" . However, you then go on to describe a scenario in which unnecessary bonding can result in a hazard for those outside of the house - with which I agree. Am I missing something?

As EFLI has said (and as we've discussed many times before), it's just like the outside tap. If that tap and pipework is nowhere near the ground (hence not 'extraneous') and is connected via copper pipe going through the wall to, say, a plastic plumbing system, then to unnecessarily bond that copper pipe would, again, introduce a potential hazard for those outside who touched the tap whilst standing on (possibly wet) ground. So, again, if the pipe is not 'extraneous', then it's safer (for those outside) not to bond.

Kind Regards, John

 

[JohnW2]

Question is TN-C-S earthing or bonding? As it does not always under fault conditions connect to true earth?

Can you clarify that question?

If you're talking about bonding within a TN-C-S installation .... Main bonding is probably at its most important in a TN-C-S installation, since the (extremely small) probability of the installation's 'earth' (MET, CPCs etc) being at a substantially different potential from true earth is at its greatest with TN-C-S. In that situation, the purpose of Main Bonding is to minimise the pd between the installation's earth and any extraneous-c-ps (which are connected to 'true earth' - even if that means raising the potential of the ground surrounding the extraneous-c-ps to close to the potential of the TN-C-S 'earth'.

Kind Regards, John

 

[EFLImpudence]

Question is TN-C-S earthing or bonding?

It is earthing - to cause ADS when exposed-conductive-parts become live.
Radiators are not exposed-c-ps.

As it does not always under fault conditions connect to true earth?

That is why we bond parts which do.

 

[ericmark]

With TN-C-S where the neutral/earth is lost then there is no connection to true earth but all parts are still bonded.

 

[JohnW2]

With TN-C-S where the neutral/earth is lost then there is no connection to true earth but all parts are still bonded.

Indeed so - but as EFLI and I have said, that it probably the situation in which it is the most crucial that any extraneous-c-ps are effectively bonded. If not, you would potentially have the installation's CPCs (hence exposed-c-ps) at a high potential relative to true earth, in possible proximity to (unbonded) extraneous-c-ps which were at true earth potential - aka a serious (albeit extremely rare) hazard.

Kind Regards, John