Main Bonding

[JohnW2]

I couldn't have a plastic gas supply pipe in my garage due to the risk of it melting in a fire, but you appear to have a plastic gas meter. I have no idea what would prevent a plastic gas meter from melting in the event of a fire in the garage.

Good point. My understanding is that plastic gas pipes are prohibited within any type of domestic building but, as you observe, plastic gas meters seem to be becoming more common.

It seems apparent that so many of these rules and regulations are not actually meant to make sense

 

[SUNRAY]

Both the gas pipes in the garage are extraneous conductive parts and therefore will need to be bonded - both are metal pipes which are buried underground.
If applying 544.1.2 fully then it's just the consumers side after the meter to be bonded, however with the prevalence of plastic gas meters, flexible stainless connectors and no guarantee that a proper metal bracket has been used, both sides should be bonded. This also partially mitigates large current flow through the gas meter and connecting flexible pipes in the event of some fault.

Assuming 4mm² SWA 3 core with one core used as a CPC, that's 4mm² plus the armour.
3 core 4mm² SWA has an armour size of about 23mm² steel, or equivalent conductivity of ~3mm² copper. Note that this is conductivity only, not the calculation for use as a CPC which is entirely different.
Combined total of about 7mm².

If this really is a TN-S supply, then minimum bonding size 6mm² copper, however there are no real TN-S supplies any more, even if they may appear that way.
For TN-C-S, or more specifically where PME conditions apply, the minimum size is 10mm² copper.

The most obvious solution is the extend the 10mm² bonding from the loft junction box to the garage, terminate at an earthing terminal there, add bonding to both gas pipes, and a further 10mm² to the consumer unit in the garage.
Existing SWA armour & core left connected.

Had this been a new installation, then 3 core 10mm² SWA to the garage should have been used. Replacing the 4mm² SWA and T&E back to the origin could still be an option for added capacity such as adding electric vehicle charging in the garage.;

And 10mm² between MET and gas pipe within 600mm of entering the house and before any tee.
We know there is an existing 10mm² gas bond to the boiler but no other details.

 

[EFLImpudence]

And 10mm² between MET and gas pipe within 600mm of entering the house and before any tee.

That is not correct.

544.1.2 The main protective bonding connection to any extraneous-conductive-part such as gas, water or
other metallic pipework or service shall be made as near as practicable to the point of entry of that part into the
premises.

Where there is a meter, isolation point or union, the connection shall be made to the consumer’s hard metal
pipework and before any branch pipework. Where practicable the connection shall be made within 600 mm of the
meter outlet union or at the point of entry to the building if the meter is external.

Although it has to be said the second part is not ideal from an electrical consideration

 

[SUNRAY]

That is not correct.

544.1.2 The main protective bonding connection to any extraneous-conductive-part such as gas, water or
other metallic pipework or service shall be made as near as practicable to the point of entry of that part into the
premises.

Where there is a meter, isolation point or union, the connection shall be made to the consumer’s hard metal
pipework and before any branch pipework. Where practicable the connection shall be made within 600 mm of the
meter outlet union or at the point of entry to the building if the meter is external.

Although it has to be said the second part is not ideal from an electrical consideration

OK so shoot me, it still requires 3 bonds:
1/ Rising main,
2/ After the meter (although some discrepancy between documents as some say as it requires bonding at point of entry to the building),
3/ Point of entry to the house (which my original comment is from gas safe documents)

 

[JohnW2]

OK so shoot me, it still requires 3 bonds:
1/ Rising main,
2/ After the meter (although some discrepancy between documents as some say as it requires bonding at point of entry to the building),
3/ Point of entry to the house (which my original comment is from gas safe documents)

It's surely OR, rather than AND, isn't it. Despite the confusions and electrical illogicalities surrounding some of the regs, it is surely the case that one gas service pipe only needs one main bond, isn't it?

 

[SUNRAY]

It's surely OR, rather than AND, isn't it. Despite the confusions and electrical illogicalities surrounding some of the regs, it is surely the case that one gas service pipe only needs one main bond, isn't it?

As I read it a pipe between 2 buildings requires bonding at the point of entry to both buildings to the electrical services in that building (although as mentioned there is discrepancy between documents where in the supply building) and both sides of the meter if they're both extraneous and there is no isolating section.

 

[JohnW2]

As I read it a pipe between 2 buildings requires bonding at the point of entry to both buildings to the electrical services in that building (although as mentioned there is discrepancy between documents where in the supply building) and both sides of the meter if they're both extraneous and there is no isolating section.

Admittedly, I'd half-forgotten the context when I wrote, but ....

...what you write may well be correct, given that the pipe 'between buildings' is buried, but it seems a little complicated. If the earth from the house is being exported to the garage, do house and garage count as the same equipotential zone? If they do, then, whilst (one) main bond would certainly be required where the supply pipe enters the garage, I'm not sure that bonding on entry to the house would also be required?? I'm not sure. I would think that having a supply pipe buried between the meter and the house it supplies is pretty unusual - I wonder why the meter was not in (or 'on') the house, in the usual way?

Whatever, at most it's surely only two bonds - any third one would seemingly be redundant? Even the confusing reg does not suggest that

 

[SUNRAY]

Admittedly, I'd half-forgotten the context when I wrote, but ....

...what you write may well be correct, given that the pipe 'between buildings' is buried, but it seems a little complicated. If the earth from the house is being exported to the garage, do house and garage count as the same equipotential zone? If they do, then, whilst (one) main bond would certainly be required where the supply pipe enters the garage, I'm not sure that bonding on entry to the house would also be required?? I'm not sure. I would think that having a supply pipe buried between the meter and the house it supplies is pretty unusual - I wonder why the meter was not in (or 'on') the house, in the usual way?

Whatever, at most it's surely only two bonds - any third one would seemingly be redundant? Even the confusing reg does not suggest that

Which one are you suggesting to ignore?

 

[JohnW2]

Which one are you suggesting to ignore?

What is your third one, after one has installed one as near as practicable to the point of entry into each building (or the regs' silly suggestion about 'after the meter' in the case of the garage) ??

 

[SUNRAY]

What is your third one, after one has installed one as near as practicable to the point of entry into each building (or the regs' silly suggestion about 'after the meter' in the case of the garage) ??

Is the incoming main not extraneous?

 

[JohnW2]

Is the incoming main not extraneous?

Of course it is (in fact, potentially the 'most important' extraneous-c-p), and that needs to be bonded where it enters the garage (or, alternatively in the regs' silly place ).

I guess I therefore have to change my question to .... "What are your other two?"

 

[Spikes Mavic]

Both the gas pipes in the garage are extraneous conductive parts and therefore will need to be bonded - both are metal pipes which are buried underground.
If applying 544.1.2 fully then it's just the consumers side after the meter to be bonded, however with the prevalence of plastic gas meters, flexible stainless connectors and no guarantee that a proper metal bracket has been used, both sides should be bonded. This also partially mitigates large current flow through the gas meter and connecting flexible pipes in the event of some fault.

Assuming 4mm² SWA 3 core with one core used as a CPC, that's 4mm² plus the armour.
3 core 4mm² SWA has an armour size of about 23mm² steel, or equivalent conductivity of ~3mm² copper. Note that this is conductivity only, not the calculation for use as a CPC which is entirely different.
Combined total of about 7mm².

If this really is a TN-S supply, then minimum bonding size 6mm² copper, however there are no real TN-S supplies any more, even if they may appear that way.
For TN-C-S, or more specifically where PME conditions apply, the minimum size is 10mm² copper.

The most obvious solution is the extend the 10mm² bonding from the loft junction box to the garage, terminate at an earthing terminal there, add bonding to both gas pipes, and a further 10mm² to the consumer unit in the garage.
Existing SWA armour & core left connected.

Had this been a new installation, then 3 core 10mm² SWA to the garage should have been used. Replacing the 4mm² SWA and T&E back to the origin could still be an option for added capacity such as adding electric vehicle charging in the garage.;

But I thought that the 10mm bonding from the MET to the Meter had to be continuous, if I put in a earthing terminal before the meter it wil have broken the continuous run !

 

[EFLImpudence]

But I thought that the 10mm bonding from the MET to the Meter had to be continuous,

Nope.

 

[Spikes Mavic]

He means an electrically isolating section/fitting in the incoming gas pipe, but I don't think (although I may be wrong!) that many domestic gas installations actually have them.

NO, it does not have one of those, but it seems that I have to bond to the outlet of the meter and the riser coming into the garage, not sure how I am going attach a bonding to that, any ideas ?.

 

[Spikes Mavic]

Nope.

That is good then so will pull through a the 10mm from the MET to a earthing block in the garage, then 10mm to the CU, outlet pipe of gas meter, and the gas riser , job done !.
ps: The difficult part is attaching a bond to the riser, not sure how to go about doing that, would have to be some sort of heavy clamp that will dig into the steel pipework, just the normal SS steal straps wond do I suspect !