Why bonding on gas pipe?

[vonsworld]

Hello

A simple question just to satisfy my curiosity!

I need to have the bonding replaced between my consumer unit and the incoming gas pipe, which are next to each other.

I know this is done so that the copper pipes in the house are earthed, but what potential faults can cause the pipework to become live?

For example, could a fault in the boiler or electric shower cause live pipes? Or a fault outside the property maybe cause the incoming gas pipe to become live?

Once the bonding is connected, if the gas pipe is underground does this act as an earth to supplement the existing earth from the supplier?

Thanks

 

[EFLImpudence]

I know this is done so that the copper pipes in the house are earthed,

No, it is done to ensure that the pipe coming out of the ground(THE earth) is at the same potential(Voltage) as your electrical installation earth.

but what potential faults can cause the pipework to become live?

It is not done because of that.

For example, could a fault in the boiler or electric shower cause live pipes?

Yes but then the overcurrent protection (MCBs etc.) will disconnect the supply instantly.

Or a fault outside the property maybe cause the incoming gas pipe to become live?

It could but the bonding(joining electrically) will ensure that all parts in your house are at the same potential so you do not get too much of a shock during the fault until the power is disconnected.

Once the bonding is connected, if the gas pipe is underground does this act as an earth to supplement the existing earth from the supplier?

It does not need supplementing.
Parts are bonded because they are already earthed by one means or another.

 

[ericmark]

One would hope that the gas pipe is not connected to true earth and bonded to house, as under fault conditions enough current could flow to rupture any flexi gas pipe, so there should be an isolating block some where.

 

[Harry Bloomfield]

Once the bonding is connected, if the gas pipe is underground does this act as an earth to supplement the existing earth from the supplier?

Hopefully not - the bonding is to attempt to ensure that all metalwork in a building, is at the same potential.

 

[davelx]

Hopefully not - the bonding is to attempt to ensure that all metalwork in a building, is at the same potential.

Generally it will. It's a parallel path to earth so will reduce Ze.
That's why you disconnect the MPBs when measuring Ze.

 

[ebee]

The idea of bonding is to make sure that all parts of the installation are at very much equal potential.
So if your electrical earth from your electricity supplier and your water main, gas main, structural steel etc etc pick up another voltage (primarily earth voltage} they are bonded together so virtually no difference is between them.
Take a bird on an over head mains transmission line, ,i could be thousands of volts, but if the bird is touching only that it will have no effect on that bird. If we have another voltage within touch then the potential difference could kill the bird.
Our things all around us can pick up voltages but they could all be of different voltages - your electrical earth from your supplier could be derived from a transformer that is earthed quite a distance away. If there is heavy industry running close your home then the earth you get from your supplier could quite easily be 35 volts different to the earth in your garden.
So if you have a lead/copper pipe running from your local soil or some girders and you can touch them at the same time and including with your electrical earthed appliances such as your washing machine or fridge freezer etc then all these things need a big thick cable to join them together and their incoming voltage does not matter too much so long as they are all the same voltage (or substantially the same voltage).

Your whole house could be at 240V different to your neighbours but so long as you only touched things connected to your house and not anywhere else you could live life just as that bird does.

Bonding conductors are equalising conductors. and hopefully not far off the potential of the soil near you.
That is why some thought needs to be given when wiring a hot tub or a Car EV charger, you need to avoid two installations with different earth voltages which means not having two different earthing systems close together.

 

[Harry Bloomfield]

Generally it will. It's a parallel path to earth so will reduce Ze.

It's not intended to be a parallel path to earth..

 

[ericmark]

great answer.
So if one was standing in their front garden soil under a fault, would the pipe thats bonded give the same fault potential to the soil aswell? As the pipe will be running under the soil to the property.

Not quite, with TT or TN-S that is true, but most people have TN-C-S or PME, the problem is Loss of PEN and the reports seem to say this is becoming more of a problem. a water pipe is water cooled, so it can take a huge current, however the same is not true with gas, and there have been many fires reported, they tend to blame copper theft, but can just as easy be road works, but a simple isolation block between the pipes in your house and pipes in the street can remove the danger, as long as the bonding wire is connected to correct side of the isolation block, with plastic gas pipes no real problem of course.

That is why some thought needs to be given when wiring a hot tub or a Car EV charger, you need to avoid two installations with different earth voltages which means not having two different earthing systems close together.

@ebee has made a good point, with items like caravans the fire regulations require some thing like a 2 meter gap between the caravan and any building, so a caravan supplied with TT and a building supplied with TN-C-S are far enough away from each other to be safe, the gradient between the two means any animal human or otherwise has enough gap.

I would have thought with EV cars fire regulations would also ensure they can't be parked too close to the building, however I have seen the charging points attached to the building, this is OK if there is a method of auto disconnection, which includes the earth bonding, so the charge point has a monitoring system to auto disconnect if the PEN is lost. This is why granny chargers should only be used in an emergency.

 

[davelx]

It's not intended to be a parallel path to earth..

I know - but it doesn't - it IS a parallel path to earth, even though that is not its intended purpose. The electrons don't know the difference.
The question was "Once the bonding is connected, if the gas pipe is underground does this act as an earth to supplement the existing earth from the supplier?"
The answer is "Yes"

 

[EFLImpudence]

if a gas pipe is bonded and it goes underground;

If it doesn't go underground then it needn't be bonded.

touches the concrete below the joists, will it make the whole room floor at same potential?

It is the ground which makes the pipe the same potential and so it has to be bonded to the electrical earth.

That is why we call it 'earth'.

 

[Harry Bloomfield]

if a gas pipe is bonded and it goes underground; touches the concrete below the joists, will it make the whole room floor at same potential? Please some1 answer me. Ty

Neither dry concrete nor dry joists, are good conductors, so no it will not much affect the potential of the floor. The risks come with good conductors, which are not bonded to your earth, that accidentally become live - where you make contact with both it and something which is earthed.