No equipotential Bonding on Gas Meter

[ericmark]

Metal parts within the house are bonded for two reasons, one it stops a fault in one room being taken into another room, so if a dog knocked over a standard lamp and the bulb smashed on a radiator it would not make all radiators in the house live, the second is so if there is a supply fault items earthed in the house are same polarity throughout the house so present no danger even if at 230 volt above true earth.

The second fault means if a gas pipe is bonded before the insulating pipe it would try to carry the current due to the faulty TN-C-S supply, this could melt the gas pipe which is clearly a danger, it is unlikely to melt a water pipe as they are water cooled. Where the water supply is in a metal pipe that would likely stop the current going through the gas pipe, and with a TT supply it really does not matter where the earth goes, houses are now RCD protected so bonding to stop faults passing from room to room is no longer really required.

So the point is the bond must be were if the TN-C-S supply is damaged that the earth current will not damage the gas pipe. Never mind regulations look at common sense. It also needs to be where some one working on the meter will not get a shock, so all metal within an enclosure should be insulated or bonded, having one pipe bonded to house earth and other pipe bonded to true earth within an enclosure is clearly not right.

There must be a procedure for gas workers, it may be that a earth clamp is fitted before removing meter, I am not gas so don't know the procedure, I know with my house the gas pipe is bonded as it enters the garage, this was to 16th Edition, the only earth at the meter is from the gas pipe that goes through the wall into the garage. So unless the person working on the meter is given assess to garage they would not know if bonded or not.

I assume there is an insulating section to stop TN-C-S faults damaging the gas pipe, although there have been a number of reports of fire when copper is stolen from sub-stations so it would seem this is not always the case.

So over to the gas guys to explain their safety procedure.

 

[bernardgreen]

Metal parts within the house are bonded for two reasons, one it stops a fault in one room being taken into another room, so if a dog knocked over a standard lamp and the bulb smashed on a radiator it would not make all radiators in the house live,

If the radiator that is Live due to dog activity is bonded to the radiator in the next room then the hazard is carried via the bond wire to the other room. The hazard is removed only if the radiator is connected to Earth ( or CPC ) with sufficlently low impedance that enough fault current flows to ensure a protective device can operate. (MCB, RCD or fuse in the plug for the standard lamp )

 

[FiremanT]

Technical_Bulletin_102.pdf

 

[EFLImpudence]

, if the bonding was at the inlet to the meter and the meter was then removed,then the bonding would not be effective,

Ah - but it would. That is the point.

That is the fundamental misunderstanding. It is the incoming pipe which introduces a hazard and gives rise to the need for bonding; not the internal pipework.

That is why, with plastic incoming pipes no main bonding is required.

 

[FiremanT]

While i am not an electrician, and I do struggle with the whole concept of bonding, apart from the obvious bits, I have noted EFL's constant assertion that the gas regs are in opposition to electric ones. However, a quick Google found this:

Purpose of Equipotential Bonding

It is important to note that the reference above is always to metal pipes. If the pipes are made of plastic, they need not be main bonded.
If the incoming pipes are made of plastic but the pipes within the electrical installation are made of metal, the main bonding must be carried out, the bonding being applied on the customer side of any meter, main stopcock or insulating insert and of course to the metal pipes of the installation.

 

[EFLImpudence]

That is, quite simply, wrong.

 

[ianmcd]

Ah - but it would. That is the point.

That is the fundamental misunderstanding. It is the incoming pipe which introduces a hazard and gives rise to the need for bonding; not the internal pipework.

That is why, with plastic incoming pipes no main bonding is required.

there was a programme a while back that was supposed to address this, they were called insulation bonds and were fitted to metal services and was basically a metal fitting interrupted by rubber to stop any transfer of any electrical current, they were also for some mad reason fitted to PE services which I will never understand, the reason for bonding gas pipes is that in theory if someone cut the pipe and there was an earth leakage that it could arc as the pipe is split and cause a source of ignition, the insulation bonds were about early corrosion of metal gas mains due to stray current

 

[EFLImpudence]

The gas companies do not want electrical current, in the event of a fault, flowing in their pipes. This is fair enough.

Main bonding is fitted to metal parts which are earthed by the ground entering the premises - an extaneous-conductive-part.
This is because that earth might/will be at a different potential (voltage) to the electrical installation earth.
So a main bonding conductor is used to the equalise that potential difference by connecting the incoming metal part to the installation main earthing terminal.

Insulating sections are intented to separate the incoming metal pipe from the electrical installation. However, that does not prevent that part being an extraneous-conductive-part to the premises. If the incoming pipe is not bonded you could, therefore, get a shock by touching the meter outlet and inlet pipes and, as you say disconnection could cause a spark.

That the gas companies are allowed, by forbidding connection to the incoming pipe, to override electrical safety does not alter the situation.

 

[ericmark]

there was a programme a while back that was supposed to address this, they were called insulation bonds and were fitted to metal services and was basically a metal fitting interrupted by rubber to stop any transfer of any electrical current, they were also for some mad reason fitted to PE services which I will never understand, the reason for bonding gas pipes is that in theory if someone cut the pipe and there was an earth leakage that it could arc as the pipe is split and cause a source of ignition, the insulation bonds were about early corrosion of metal gas mains due to stray current

So that's also why water pipes are bonded is it? The water may go on fire! Bonding is to ensure all items are at same polarity to stop electric shocks, and it is likely at some point the bonded metal work is also connected at some point to earth, and so with the lamp example it is likely the fuse, MCB, or RCD will trip making it safe.

It is true that if the earth electrode is made of copper it can cause erosion of iron pipework also earthed or of course the hull of a boat, the latter often has sacrificial anodes made of zinc to reduce the erosion. Same can happen to the steel wire armour of a cable if the plastic sheaf is damaged.

I suppose the same could happen with a coax cable feeding power to the house, although never seen it happen. So there is a move to also have an earth electrode at the house even with a TN supply, however it would need to be made from same material as the boards earth electrode as it would form part of the PME so could not be just a random lump of metal.

With plastic pipes in the street it is I suppose possible that a shared pipe to two premisses could introduce fault polarity from one premises to another if connected together using steel pipe plastic coated. So either there needs to be an earth on that steel pipe, or that steel pipe would need an isolating block some where.

It's all well and good saying with a new estate this must happen, but what one has to consider is what will happen with an old estate? It is clearly a steel pipe supplying my house, what is not clear however is does that pipe only supply my house, so since we don't know, there is no option but to bond to earth to ensure it presents no danger.

Point to remember there is no fuse in neutral or earth, so if there is a fault on a TN-C-S supply no fuse will rupture making it safe.

 

[bernardgreen]

it is I suppose possible that a shared pipe to two premisses could introduce fault polarity from one premises to another if connected together using steel

Which is the case with my cottage and adjacent retail unit. Originally they were one property with a TT electricty suppy into the retail unit and water supply to the cottage. They are now separated with different ownership. I now have a new PME electricity supply the cottage but still supply water to the retail unit. The two supplies come from different street cables, no common Neutral. The water pipe from cottage to retail unit has to have a 1 metre plastic isolation section.

As mentioned faults or metal theft which open circuits the Neutral at the substation can create very large fault currents in bonding wires connected to metal supply pipes. The current is that which would have returned to the substation along th Neutral. Where the supply pipe is very low impedance to Ground then the fault current can melt bonding wires

 

[FiremanT]

The gas companies do not want electrical current, in the event of a fault, flowing in their pipes. This is fair enough.

Main bonding is fitted to metal parts which are earthed by the ground entering the premises - an extaneous-conductive-part.
This is because that earth might/will be at a different potential (voltage) to the electrical installation earth.
So a main bonding conductor is used to the equalise that potential difference by connecting the incoming metal part to the installation main earthing terminal.

Insulating sections are intented to separate the incoming metal pipe from the electrical installation. However, that does not prevent that part being an extraneous-conductive-part to the premises. If the incoming pipe is not bonded you could, therefore, get a shock by touching the meter outlet and inlet pipes and, as you say disconnection could cause a spark.

That the gas companies are allowed, by forbidding connection to the incoming pipe, to override electrical safety does not alter the situation.

View attachment 160635

So what if a faulty appliance makes contact with the copper gas pipe, or copper radiator pipe within the premises? That copper pipe itself, I understand, is an extraneous conductive part?

 

[aptsys]

Metal parts within the house are bonded for two reasons, one it stops a fault in one room being taken into another room, so if a dog knocked over a standard lamp and the bulb smashed on a radiator it would not make all radiators in the house live, the second is so if there is a supply fault items earthed in the house are same polarity throughout the house so present no danger even if at 230 volt above true earth.

Incorrect. Bonding is not for fault protection.

 

[EFLImpudence]

So what if a faulty appliance makes contact with the copper gas pipe, or copper radiator pipe within the premises? That copper pipe itself, I understand, is an extraneous conductive part?

If you mean things like Eric's dog and standard lamp, we do not have to consider such random things for pipes any more than we would for any other metal object that is not part of the electrical system.

If you mean, for example, the pipe in an electric shower - then if you consider it likely that a live conductor might contact it (probably unlikely) then it will be an Exposed-conductive-part and should be earthed.

Pipes which are connected to appliances like boilers will be earthed by the appliance CPC(earth wire). See my diagrams.

 

[Hot&Cold]

If I get a smart meter fitted which is outside,

northernchappy,if you are still reading your initial post Your post has made some departures

If the gas meter installer actually exchanges your dumb meter to a so called smart,then they will leave advisory paperwork,labels & advice. The installers competence is limited by qualifications.