18th edition - where to bond gas supply pipe, if at all?

[fjhugh]

Evening,

SGN have replaced the street's gas pipes by feeding a new PE plastic one in through the existing steel pipe. The meter is in cupboard under the stairs. TNCS earthing.

SGN have fitted a new 'electrically insulated' head just before the meter. I have tested and there is no continuity between the steel supply pipe and the consumer's pipework on the other side of the meter. The consumer pipework does not re-enter the ground after this insulated section. Consumer pipework is therefore not extraneous nor require bonding as per 18th ed 411.3.1.2.

That leaves the 20cm of original supply pipe. I have tested and it has resistance of 0.0012 ohms to the MET so is an extraneous conductive part.

When SGN finished, they half taped up this supply pipe in black insulation tape.

Would you:

1) Bond the supply pipe before the meter?

- Disadvantage being it's technically against 544.1.2 as before the meter outlet. And as I can't imagine the neighbours have suddenly switched round their bonding, this steel gas pipe might act as an earth rod for the street should there be a lost neutral. I don't like the idea of the diverted neutral travelling in an old rusty-jointed steel pipe containing plastic and gas.

2) Alternatively, forget bonding and finish wrapping the supply pipe up in tape then wrap again in self-amalgamating tape.

- That way at least no diverted neutral currents would flow down pipe and there is no risk of earth potential if you touch the tape. Disadvantage being the pipe is only safe as long as the tape remains in tact to protect it.

I'm struggling to see how SGN can do this work and potentially leave each house with a 'new' conductive part now isolated from any bonding that might have been present?!

 

[SUNRAY]

When i moved into this house in 1994 the the incoming steel gas supply had a copper wire of about 4mm size so I guess 7/0.036" clamped to it with what I'll describe as a plain steel tape and a buckle, which wasn't actually tight.
I replaced the fuse box and updated the earthing/bonding arrangements quite quickly. However there was a lot of discussion at the time which side of the meter the gas connexion should be so when i replaced the original clip I also added another where my side drops back down into the concrete floor.

Recently we also had the plastic liner installed and installed the insulated head and as such the steel pipe under the public footpath has been cut off. Effectively I now have a ~15m steel earthrod 5-6Ω to MET. I see no dissadvantage to leaving it connected.

I believe SGN are supposed to wrap the whole of the exposed steel with a white plastic sleeve, they fitted it on minebetween the earthclip and the head but the 50mm or so below the clip is not covered.

I have 2 new questions:
1) Why is it a red handle on the isolating valve when any other gas tap is yellow?
2) Why is the black tape they apply always such a scrappy mess?

 

[sparxxxx]

When SGN finished, they half taped up this supply pipe in black insulation tape.

I would imagine they should have completely wrapped it, and then it would no longer be conductive (touchable) and therefore impossible to introduce a voltage into the premises.

EDIT - just seen photos, they take ages to appear, that pipe wrapping should surely be taken through the floor boards, so that their is no conductive connection in the premises

 

[JohnW2]

SGN have replaced the street's gas pipes by feeding a new PE plastic one in through the existing steel pipe. The meter is in cupboard under the stairs. TNCS earthing. ... SGN have fitted a new 'electrically insulated' head just before the meter. ... That leaves the 20cm of original supply pipe. I have tested and it has resistance of 0.0012 ohms to the MET so is an extraneous conductive part. ...Would you: 1) Bond the supply pipe before the meter? -

Technically, yes. As you say, there is 20cm of extraneous-c-p, and, regardless of confusion created by the regs, in electrical terms that clearly should be bonded.

... Disadvantage being it's technically against 544.1.2 as before the meter outlet.

Quite apart from the confused/confusing (and essentially incorrect) wording of the regs, there is nothing there to say that you can't bond whatever you like (in addition to whatever the regs appear to require!) - and, as above, bonding of that small bit of extraneous-c-p is, in strict electrical terms, 'required'.

Bonding on the consumer's side of the meter would obviously be silly in your case, and (despite what many seem to think) nor is it actually required by the regs. 544.1.2 (and other regs) only relate to main bonding when it is required (to bond extraneous-c-ps). Nothing in the regs (not even 544.1.2) requires one to main bond something which is not an extraneous-c-p.

That's my view, anyway!

Kind Regards, John

 

[ericmark]

The worry is if you bond the incoming pipe before the isolation block then if you loose the PEN it could try to earth the street through the gas pipe, and melt the pipe and set gas on fire, however once in the house any metal moving from room to room can result in it transmitting a fault, so if for example the walls are made of plaster board on metal instead of wood, and the plasterer was to in error to put a fixing through a cable, then that metal could take the fault into the airing cupboard, and if then the thermostat failed and the plumber had failed to glue the tun dish and water as a result ended on the floor, when Emma Shaw tried to turn off the water the resulting shock killed her, due to the line being transmitted with the internal metal work.

So if a dog knocks over a standard lamp and the bulb smashes on the radiator in that room we can see the accident and take care as a result, but if the radiator pipe work is not earthed, in another room we could touch a radiator and get a shock without being aware of the accident, so we try to earth metal which goes room to room.

Today in the bathroom for example the earthing has been reduced, it is a risk assessment, if nothing in the room is earthed, like the birds on a power line, you can touch a live wire without current flowing through your body, or with reduced flow as some capacitive and inductive linking, so where RCD protection is used, it may be safer not to bond. And as a result rules have changed.

The IET/BSi regulations guide us on how we can make electricity safe to use, but main thing is common sense, so where there is a insulating block to stop the bonding of the gas pipe in the ground, clearly this should not be by-passed.

 

[JohnW2]

....The IET/BSi regulations guide us on how we can make electricity safe to use, but main thing is common sense, so where there is a insulating block to stop the bonding of the gas pipe in the ground, clearly this should not be by-passed.

Indeed - although, as I said, if there is a touchable bit of metal pipe (even if only the 'conduit for a plastic pipe) on the supplier's side of the "insulating block", that is an extraneous-c-p which, strictly speaking, should be bonded. However, there is a balance of risks, and if there is only 20cm of it (probably not all that easily 'accessible'), as in the OP's case, common sense would probably suggest that one should not bond it.

The requirement in the regs to 'main bond' pipework on the consumer's side of an insulating section (or 'insulating meter') is quite ridiculous, and was presumably written by someone who has no understanding of the concept and purpose of main equipotential bonding!!

Kind Regards, John

 

[fjhugh]

Thanks all, I'm inclined to agree.

My concern is while it is only 20cm of pipe, it is unfortunately very accessible at entrance to a small cupboard where one would likely have a leg or foot in contact with the pipe whilst touching the metal CU on the opposite wall.

And as you, with a lost PEN, if I bond it I don't fancy the pipe being the earth rod for the street, especially as the neighbour's pipes are now likely to be insulated and not bonded.

I think I will get back to the distribution company and ask them to sleeve/insulate the pipe, though I expect some push back and and probably be told it is an 'electrical issue'. Interestingly, if you look at IGEM G/5 Edition 2 guidance for multiple occupancy buildings, 11.2.3 states:

"exposed pipe between the ground and insulating fitting shall be encapsulated in an approved insulating sleeve or otherwise protected to prevent physical contact with surface of the pipe. The wrapping shall be marked 'electric shock hazard, do not remove'".
​

I wonder if there is an equivalent standard for single domestic dwellings. Might explain why they at least partially covered the pipe in tape!

 

[JohnW2]

Thanks all, I'm inclined to agree. ... My concern is while it is only 20cm of pipe, it is unfortunately very accessible at entrance to a small cupboard where one would likely have a leg or foot in contact with the pipe whilst touching the metal CU on the opposite wall.

Fair enough - that obviously makes it, at least theoretically, more desirable to bond it.

Kind Regards, John

 

[sparxxxx]

more desirable to bond it.

It most certainly is not, before any of these works the whole street/area would have multiple main gas bonds to safely carry any spurious external voltages. But now all of these bonds will be removed, which means all of those voltages present in the area will be going through his solitary bonding cable - not a good situation.

 

[SUNRAY]

Thanks all, I'm inclined to agree.

My concern is while it is only 20cm of pipe, it is unfortunately very accessible at entrance to a small cupboard where one would likely have a leg or foot in contact with the pipe whilst touching the metal CU on the opposite wall.

And as you, with a lost PEN, if I bond it I don't fancy the pipe being the earth rod for the street, especially as the neighbour's pipes are now likely to be insulated and not bonded.

I think I will get back to the distribution company and ask them to sleeve/insulate the pipe, though I expect some push back and and probably be told it is an 'electrical issue'. Interestingly, if you look at IGEM G/5 Edition 2 guidance for multiple occupancy buildings, 11.2.3 states:

"exposed pipe between the ground and insulating fitting shall be encapsulated in an approved insulating sleeve or otherwise protected to prevent physical contact with surface of the pipe. The wrapping shall be marked 'electric shock hazard, do not remove'".
​

I wonder if there is an equivalent standard for single domestic dwellings. Might explain why they at least partially covered the pipe in tape!

Don't forget the metal pipe is not connected to the neighbours metal pipe. So it is only the same as an earth spike.

However I'm much more aware of these sort of issues since running into a problem a while back https://www.diynot.com/diy/threads/a-real-moan-tonight.552183/

 

[SUNRAY]

It most certainly is not, before any of these works the whole street/area would have multiple main gas bonds to safely carry any spurious external voltages. But now all of these bonds will be removed, which means all of those voltages present in the area will be going through his solitary bonding cable - not a good situation.

That metal pipe is not connected to the metal pipe in other houses.

 

[sparxxxx]

That metal pipe is not connected to the metal pipe in other houses.

It is connected to the existing steel main that enters all the other houses, in the same way it enters his house.

 

[bernardgreen]

That metal pipe is not connected to the metal pipe in other houses.

There are still some places where metallic service pipes are supplied from metallic street mains.

I knew a gas meter reader who wore insulated gloves when touching meters. This was after he got a muscle jerking shock from a meter.

The "Earth" ( CPC and MET ) in the house were not at Ground potential and as a result the gas meter was not at Ground potential.

There could have been a bond MET to gas meter but there was also the connection via the gas pipe to the CPC "earth" at the gas boiler

 

[JohnW2]

It most certainly is not, before any of these works the whole street/area would have multiple main gas bonds to safely carry any spurious external voltages. But now all of these bonds will be removed, which means all of those voltages present in the area will be going through his solitary bonding cable - not a good situation.

That issue has been acknowledged.

However, the OP has indicated that this bit of exposed pipe and a nearby metal CU could easily be simultaneously touched by a person, creating the (potentially fatal) electric shock hazard which is the very thing which equipotential bonding is designed to eliminate.

As the OP has said, the ideal solution is to get the exposed bit of pipe insulated but unless/until that happens, one has to balance the risk of electric shock due to absent bonding with the risks resulting from potentially high currents flowing through the bonding conductor.

Edit: I should have added ... The balance that needs to be struck is not peculiar to the OP's situation. IF one adopted your "It most certainly is not" view, that would presumably mean that one felt that one "certainly should not" main bond any extraneous-c-p in a TN-C-S installation - which I would imagine/hope is not your view, is it?

Kind Regards, John

 

[SUNRAY]

It is connected to the existing steel main that enters all the other houses, in the same way it enters his house.

No it"s not.