earthing gas supply

[keefy22]

Hi
I have just found a card in the gas meter box outside the house advising that the earth bonding is not sufficient.I have read some of the posts and it would seem that some posts suggest that I need to run a length of 10mm earth cable between the earth in the consumer unit and the gas pipe within 600mm of the incoming side but before a junction, whilst others seem to suggest the earth wire should be attached to the point at which the gas pipe enters building. Which is correct??.(if it is when entering building there is a problem in that the pipe splits up after leaving meter and enters building at two different points.Any advise greatly appreciated.
keefy22

 

[ericmark]

It is connected to consumers side of the gas meter.
When the house is supplied with a TN-C-S supply it normally required 10mm earth cable but where a TT supply is used 6mm is big enough.
I would always use 10mm but I have seen in the past where people have jumped to conclusions and have condemned a system without first checking if a TN-C-S or TT supply.

Using common sense.
I have never stripped a gas meter down but I suspect it may electrical isolate the input and output. And it is the house pipework you are earthing so it will always be your side of meter.

With a TT supply often only 100ma or less needs to flow to trip the RCD so 6mm is really only to ensure mechanical connection as the earth rod is normally not good enough to take high currents.

With a TN-C-S system a cooker fault could result in 50 amp travelling to earth so to cover these higher currents a thicker cable is required.

The regulations have a lot of cross reference and calculations with earthing 544.1.1 gives 6mm for non TN-C-S and Table 58.8 give 10mm with TN-C-S but there are other rules which are based on neutral size and fuse size etc. which could change this and I am only talking about a normal house with nothing special.

 

[Taylortwocities]

For a house, and in most cases, the bonding should be within 600mm of the stop cock on the consumers side.

The only time I have used the "bonding at point of entry" is in flats where the gas meters are remote and several floors down from the flat.

 

[ban-all-sheds]

I have never stripped a gas meter down but I suspect it may electrical isolate the input and output..

Me neither, but if it did do that there'd be no point in bonding....

 

[gas4you]

Unfortunately there is a discrepency between eletric and gas regs.

Gas regs state that the gas pipe should be earthed within 600mm of the meter and before the first tee, whilst I understand that electric regs state at the first point of entry of the gas pipe into the building.

As a gas engineer I always have to abide with the gas regs and issue a warning notice accordingly

 

[RF Lighting]

I have never stripped a gas meter down but I suspect it may electrical isolate the input and output..

Me neither, but if it did do that there'd be no point in bonding....

Why would you need to strip it down? Surely a simple continuity test would be far easier?

 

[Steve]

A gas meter has a metal case, and the incoming and outgoing pipes are metal. How would it reliably isolate?

 

[securespark]

There's a little DP breaker inside with 3mm gap contacts?

 

[JohnD]

gas meters are removable, for replacement and testing.

In the same way that, when a boiler is removed or being repaired, a PD may exist between the various gas and water pipes that are normally connected to it, once the gas meter is disconnected, you obviously lose continuity between the upstream and downstream gas pipes

 

[swbjackson]

But if you remove the meter you put a temporary continuity bond across the pipework before hand.

Mike

 

[Steve69the69Gas]

And just to be absolutely clear,

Its 10mm2 on the outlet of the meter,within 600mm of the outlet, but before any tee.

 

[Adam_151]

And just to be absolutely clear,

Its 10mm2 on the outlet of the meter,within 600mm of the outlet, but before any tee.

Yes, or rather within 600mm, *but as close as reasonably practical* (and definatly before any T's)

To be totally correct, its not distance from the meter that matters at all, its from where it comes in to the building that matters (the electrical regs are concerned about all services capable of introducing a potential, not just those that have a meter), but in instances where these are not one and the same.. I see no harm in taking it as being the meter instead if it keeps the gas fitters happy (probably easier to find as well!)

 

[keefy22]

Thanks to all for advice
Keefy22

 

[snb]

bonding for the gas supply is the same for the gas and elec regs.

it states for both that it should be within 600mm of service meter ,or at point of entry to building if external and must be before any branch(tee).

the size of the bonding has to be at least half the size of the main bonding conductor

 

[Spark123]

Or in the case of TN-CS (PME), it should be verified with the Distribution Network Operator as they can require a larger size.