main equipotential bonding to gas

[JohnW2]

... none of the gas pipes are now in contact with the ground, except for the old one which fed the original meter and has now been disconnected from any other pipework in the house.

Strictly speaking the old pipe should still be main bonded so don't go playing with it.

I think that's a very important point, and one which sometimes goes overlooked (or perhaps misunderstood), particularly in old properties. As you imply, the requirement for bonding applies to any pipe (or other metallic object) which, having been 'in contact with the ground' enters the building, regardless of whether the pipe is 'in use' or not.

I had that issue in my house. When I moved in, there were several (clearly many decades old) unused metal pipes appearing through the cellar walls - presumably left-overs of previous water supply arrangements. Although not in use, they all theoretically required main bonding (they have now all 'gone').

Kind Regards, John

 

[JBR]

I appreciate your advice and am quite sure everything is safe here, as none of the gas pipes are now in contact with the ground, except for the old one which fed the original meter and has now been disconnected from any other pipework in the house.

Strictly speaking the old pipe should still be main bonded so don't go playing with it.

(The main reason I asked earlier was that someone suggested that pipes should be connected/bonded to a point near or at the electricity meter. I think they might have said 600mm.)

It will be connected to the Main Earthing Terminal.
600mm. has nothing to do with it.

The MET will be either a block near the meter or consumer unit or the earth bar in the consumer unit.

Thanks again. I'm sure you're right, although the bonding cable must then go about 20 feet from where it disappears under the floor to the meter or CU which are above a doorway on the other side of the room. I presume this is acceptable.

Just to clarify, though, the pipe that is bonded is the one that is part of the pipework currently in use. The pipe that used to feed into the old gas meter is not bonded, although it is not connected to anything else in the house. Should it be bonded too?

 

[JBR]

... none of the gas pipes are now in contact with the ground, except for the old one which fed the original meter and has now been disconnected from any other pipework in the house.

Strictly speaking the old pipe should still be main bonded so don't go playing with it.

I think that's a very important point, and one which sometimes goes overlooked (or perhaps misunderstood), particularly in old properties. As you imply, the requirement for bonding applies to any pipe (or other metallic object) which, having been 'in contact with the ground' enters the building, regardless of whether the pipe is 'in use' or not.

I had that issue in my house. When I moved in, there were several (clearly many decades old) unused metal pipes appearing through the cellar walls - presumably left-overs of previous water supply arrangements. Although not in use, they all theoretically required main bonding (they have now all 'gone').

Kind Regards, John

Thanks for your input. The old gas pipe which was connected to the 'input' side of the old gas meter, and which is no longer in use and is no longer connected to anything in the house, does indeed travel through the ground outside. Only the pipe which was connected to the 'output' side of the gas meter, and is still connected to the rest of the gas pipe-work that is still in use, is bonded.

Should the old gas pipe that is no longer in use also be bonded? Should I simply connect (electrically) the two pipes which used to be connected to the old gas meter?

Somehow, that doesn't seem sensible to me, as the old pipe isn't connected to anything. In fact, were it not passing through a solid floor, I'd try to remove it!

 

[JohnW2]

Thanks for your input. The old gas pipe which was connected to the 'input' side of the old gas meter, and which is no longer in use and is no longer connected to anything in the house, does indeed travel through the ground outside. Only the pipe which was connected to the 'output' side of the gas meter, and is still connected to the rest of the gas pipe-work that is still in use, is bonded. Should the old gas pipe that is no longer in use also be bonded?

As EFLI and myself have said, theoretically yes

Should I simply connect (electrically) the two pipes which used to be connected to the old gas meter?

Having a separate bit of cable connecting those two pipes would not technically be compliant with the regulations. However, it would be compliant to use the same cable (extended by joining {e.g. at the existing bonding clamp}, if necessary, even though some people moan that such is not 'good practice') to bond both pipes.

Don't forget that, as EFLI said originally, if your new outside gas meter is now supplied in plastic pipe, and the output pipe from it does not come into contact with ground, then that pipe (the 'in use' gas pipe now entering your house) does not need bonding, although it almost certainly does not harm to leave it connected. You could therefore theoretically move the bonding cable from the 'in use' pipe to the old, now 'unused' one (illogical though that may seem - see below!) - but I would hesitate to suggest that you did remove the existing bonding without seeing the situation with my own eyes.

Somehow, that doesn't seem sensible to me, as the old pipe isn't connected to anything. In fact, were it not passing through a solid floor, I'd try to remove it!

I can understand it not sounding sensible, particularly when I suggest that one theoretical solution would be to remove bonding from the 'in use' pipework and connect it to the 'not-in-use' pipe! However, it all makes sense once one understands what main protective bonding is all about ....

... under certain, rare, fault conditions, the potential of your house's earthing system can rise to a voltage much higher than earth potential. That means that the touchable metal parts of many electrical items and appliances would rise to a high voltage above earth. If someone simultaneously touched one of those items and something connected to 'true earth', they therefore could suffer a serious electric shock, because of the potential difference between the two things they were touching.

To avoid that risk, the house is turned into an 'equipotential zone' (one of the names for main bonding is 'Protective Equipotential Bonding') so that such differences is potential cannot arise. This is achieved by connecting fairly fat bonding cables between the house's electrical system (at the 'MET' usually near {or in} the CU) and anything entering the house (like pipes) that could possibly be at 'true earth' potential. Having done that, the sort of dangerous differences in potential cannot arise. I understand that your old, unused, gas pipe does go through the ground, and is therefore probably close to true earth potential, and therefore would present a hazard if someone touched it at the same time as touching something else which was at a high potential above earth due to a fault.

You might well tell me that what is left of that old pipe could not be touched at the same time as anything else. The regulations requiring bonding of that old pipe do not make an exception about that but it would be up to you to decide to what extent you felt common sense should prevail. However, someone inspecting the electrical installation would expect to see that bonding of the unused pipe.

In considering the extent of the risk, remember that the 'in use' gas and water pipes are almost certainly connected to your house's electrical installation (and almost certainly would be even if you removed the theoretically unnecessary bonding to the 'in use' gas pipe). If it is possible to touch any of the in-use gas or water pipes at the same time as touching the old, not-in-use gas pipe (probably at true earth potential), then there is a true risk, so that bonding of the not-in-use pipe would be very wise (as well as being required by regulations).

Hope that helps.

Kind Regards, John

 

[bernardgreen]

A gas meter reader told me he is very careful if he has to wipe the glass to see the figures, this after getting a mild shock from a gas meter.

Creating and using bonding to create an equipotential area inside the house is fine.

It is not quite so good when considering things outside the house that are bonded to the MET. The risk of a person outside the house getting a shock from for example a water tap on the wall is not insignificant.

We should not ( or must not ) export the internal "earth" to power tools in the garden but we can ( even should ) export it via copper pipes to a water tap on the outside of the house.

 

[JohnW2]

A gas meter reader told me he is very careful if he has to wipe the glass to see the figures, this after getting a mild shock from a gas meter. ... Creating and using bonding to create an equipotential area inside the house is fine. ... It is not quite so good when considering things outside the house that are bonded to the MET. The risk of a person outside the house getting a shock from for example a water tap on the wall is not insignificant. ... We should not ( or must not ) export the internal "earth" to power tools in the garden but we can ( even should ) export it via copper pipes to a water tap on the outside of the house.

We've discussed this more times than I care to remember and, as you know, I essentially agree with you in concept. Some outside oil tanks/piping are another example.

I'm not so sure about "We should not ( or must not ) export the internal "earth" to power tools in the garden" ( I would have said "ought not", because I'm not sure that any regulation actually forbids it) but, apart from that, I agree with all you say. The only solution (at least, for the examples you give) would appear to be to insert an 'insulating section" in the pipe (which, for the gas pipe, would probably have to be outside the house).

However, as we've also discussed, it's more about avoiding 'minor tingles' than a major safety issue - since the chances of someone touching an outside tap or gas/oil meter, or even a Class I tool/appliance in the garden (at the same time as being in contact with truth earth) at the very moment when a fault had raised the installation's earthing system to a potential that could do them significant harm (itself very rare) must be incredibly small.

Kind Regards, John

 

[JBR]

Thanks for your input. The old gas pipe which was connected to the 'input' side of the old gas meter, and which is no longer in use and is no longer connected to anything in the house, does indeed travel through the ground outside. Only the pipe which was connected to the 'output' side of the gas meter, and is still connected to the rest of the gas pipe-work that is still in use, is bonded. Should the old gas pipe that is no longer in use also be bonded?

As EFLI and myself have said, theoretically yes

Should I simply connect (electrically) the two pipes which used to be connected to the old gas meter?

Having a separate bit of cable connecting those two pipes would not technically be compliant with the regulations. However, it would be compliant to use the same cable (extended by joining {e.g. at the existing bonding clamp}, if necessary, even though some people moan that such is not 'good practice') to bond both pipes.

Don't forget that, as EFLI said originally, if your new outside gas meter is now supplied in plastic pipe, and the output pipe from it does not come into contact with ground, then that pipe (the 'in use' gas pipe now entering your house) does not need bonding, although it almost certainly does not harm to leave it connected. You could therefore theoretically move the bonding cable from the 'in use' pipe to the old, now 'unused' one (illogical though that may seem - see below!) - but I would hesitate to suggest that you did remove the existing bonding without seeing the situation with my own eyes.

Somehow, that doesn't seem sensible to me, as the old pipe isn't connected to anything. In fact, were it not passing through a solid floor, I'd try to remove it!

I can understand it not sounding sensible, particularly when I suggest that one theoretical solution would be to remove bonding from the 'in use' pipework and connect it to the 'not-in-use' pipe! However, it all makes sense once one understands what main protective bonding is all about ....

... under certain, rare, fault conditions, the potential of your house's earthing system can rise to a voltage much higher than earth potential. That means that the touchable metal parts of many electrical items and appliances would rise to a high voltage above earth. If someone simultaneously touched one of those items and something connected to 'true earth', they therefore could suffer a serious electric shock, because of the potential difference between the two things they were touching.

To avoid that risk, the house is turned into an 'equipotential zone' (one of the names for main bonding is 'Protective Equipotential Bonding') so that such differences is potential cannot arise. This is achieved by connecting fairly fat bonding cables between the house's electrical system (at the 'MET' usually near {or in} the CU) and anything entering the house (like pipes) that could possibly be at 'true earth' potential. Having done that, the sort of dangerous differences in potential cannot arise. I understand that your old, unused, gas pipe does go through the ground, and is therefore probably close to true earth potential, and therefore would present a hazard if someone touched it at the same time as touching something else which was at a high potential above earth due to a fault.

You might well tell me that what is left of that old pipe could not be touched at the same time as anything else. The regulations requiring bonding of that old pipe do not make an exception about that but it would be up to you to decide to what extent you felt common sense should prevail. However, someone inspecting the electrical installation would expect to see that bonding of the unused pipe.

In considering the extent of the risk, remember that the 'in use' gas and water pipes are almost certainly connected to your house's electrical installation (and almost certainly would be even if you removed the theoretically unnecessary bonding to the 'in use' gas pipe). If it is possible to touch any of the in-use gas or water pipes at the same time as touching the old, not-in-use gas pipe (probably at true earth potential), then there is a true risk, so that bonding of the not-in-use pipe would be very wise (as well as being required by regulations).

Hope that helps.

Kind Regards, John

Thanks again for your very thorough explanation. There's a lot to take in here, especially for one not that familiar with electricity, although I think I understand.

As the 'in use' pipe could conceivably carry a significant voltage in a fault situation, and the 'not in use' pipe remains at or near 'true earth', the fact that they are both within a few inches of each other would suggest that it is possible for someone to touch both simultaneously and receive a shock. I hope I've got that right.

So I really need to do something about that. The simplest thing would be to connect the two pipes electrically, although you say "Having a separate bit of cable connecting those two pipes would not technically be compliant with the regulations."

You then say "However, it would be compliant to use the same cable (extended by joining {e.g. at the existing bonding clamp}, if necessary, even though some people moan that such is not 'good practice') to bond both pipes." Does this mean that I should use the existing bonding wire, strip the insulation at some point and connect that area to one pipe and the present end to the other?

From what you've told me, it does sound important that I should bond both of the pipes, so I'm a bit worried that some people would say it is not 'good practice'. Why should it not be good practice to do that?

If I have got all this right, would it be acceptable for me to do this bonding myself?

 

[JohnW2]

As the 'in use' pipe could conceivably carry a significant voltage in a fault situation, and the 'not in use' pipe remains at or near 'true earth', the fact that they are both within a few inches of each other would suggest that it is possible for someone to touch both simultaneously and receive a shock. I hope I've got that right.

Yes, that's precisely it - you have understood perfectly.

So I really need to do something about that. The simplest thing would be to connect the two pipes electrically, although you say "Having a separate bit of cable connecting those two pipes would not technically be compliant with the regulations.".

It may sound a little silly/pedantic, but the regulations tend to be very 'conservative' There are some incredibly unlikely scenarios which (one imagines) causes the regs to require your 'unused' pipe to be connected by a piece of wire to MET of the earthing system, rather than to a nearby pipe which itself is connected by a wire to that MET!

You then say "However, it would be compliant to use the same cable (extended by joining {e.g. at the existing bonding clamp}, if necessary, even though some people moan that such is not 'good practice') to bond both pipes." Does this mean that I should use the existing bonding wire, strip the insulation at some point and connect that area to one pipe and the present end to the other?

If the present wire is long enough for you to do that (connect the one wire to both pipes,with no joins in the wire) that would not only be totally compliant with the regs but would satisfy everyone as being good and satisfactory practice.

From what you've told me, it does sound important that I should bond both of the pipes, so I'm a bit worried that some people would say it is not 'good practice'. Why should it not be good practice to do that?

If you can, as above, bond both pipes with the same cable without any joins in it) then, as I said, there is no question of it not being 'good practice'. As for my comment, don't worry - some electricians have been taught that it is 'not good practice' to have any joins in a bonding cable, but there is no regulation which says that. Hence, if you had to have a join (e.g. at one of the cable clips), I do not think you should worry about that.

If I have got all this right, would it be acceptable for me to do this bonding myself?

Yes, it would. Don't forget that until you have got the old pipe bonded, there is a theoretical (incredibly small) possibility that there could be a 'significant' voltage between the old and new pipes, so you should avoid touching both simultaneously until the bonding is in place. AS a precaution, you could switch off your entire electrical system (at your CU) whilst you were doing it, but that would not prevent there being a voltage between the two pipes (until bonding is in place) if the fault resulting in the voltage difference were outside of your property - so you would still need to 'be careful' (not to touch both pipes simultaneously) until the additional bonding was in place. You need to use a proper earthing clamp to connect the wire to the old pipe. The old clamp may well still be there but,if not, they are fairly easily found to purchase. If you have to install a new clamp, make sure you clean any muck/paint/whatever off pipe before installing it.

Hope that helps.

Kind Regards, John

 

[securespark]

I found a water supply to a fairly new house today. Supply pipe was blue mdpe plastic which terminated straight into the stop cock. There was then 2" of copper pipe before it turned back into plastic. Some muppet had gone to all the trouble of bonding the copper pipe

Saw the same at 'Uddersfield Rugby Club the other week. This in a portacabin:

There were a couple of short lengths of copper a couple of inches long (I mean 50mm). The rest was plastic.

 

[JBR]

Thanks again, John. Your advice is certainly appreciated.

I'll get an earthing clamp when I can (B&Q) and fit it myself. Yes, the existing wire passes right next to the unconnected pipe, so that should be easy enough.

 

[JBR]

Done.

Thanks again.