thinking a little off the wall Gas Meter Bonding

sarusystems · Feb 17, 2012

Hi I am not sure if this will apear to be a silly question but.
If the Gas service is on the other side of the building to the electrical supply TNS
do you think it would be acceptable to use an earth rod near to the gas service rather than having
a long length of bonding cable.

Also previous contractor has cross bonded using only the earth tags threaded in to each other I am not questioning the fact of would this work but
is this a practice used by my other fellow installers

telectrix · Feb 17, 2012

what use is an earth rod tying down a gas service that is already earthed? the whole point of equipotential bonding is to tie the services to the electrical earthing system.

Dannyspark · Feb 17, 2012

You have to ask the question as to why we bond the gas/water suppy?

Ultimately what we are trying to acheive is to ensure that enough current will flow under fault conditions to ensure that the protective device operates within the required time among other things.
What you are suggesting is creating a mini TT system on the gas pipework and TT systems by design generally have a high a resistance value compared with TNS or TNCS systems.

I think you are creating a headache for yourself by going along this road as you will need to take a reading from the earth rod and do the relevant calcs to ensure that disconnection can be achieved.

I would suggest that you bite the bullet and tell the customer that you will have to run a 10mm cable from one side of their house to the other because providing you have a standard domestic TNS set up you shouldn't need to do any calcs just use the criteria laid out in your OSG.

With regard to the cross bonding issue with the earth tags being threaded into one another, this is a "Plumbers trick" in fact I would suggest that this was the water board in fact.
In fact it is unnecessary with a modern boiler as the manifold (where all the pipework connects into) is generally made of brass or similar metal and providing the gas and water are bonded then by default the entire plumbing system is bonded (unless their is some bodged plastic within the copper system).

Hope this helps.

Guest111 · Feb 17, 2012

Dannyspark,don,t forget boilers have washers between pipe and boiler also pipes aren,t solidly fixed to bracket.in this day and age when everybody is suing everbody else at the drop of a hat I still think best practice would be to link all pipes under boiler if just to cover your back,just my opinion don,t know about everyone else.

Dannyspark · Feb 17, 2012

phil d said:
Dannyspark,don,t forget boilers have washers between pipe and boiler also pipes aren,t solidly fixed to bracket.in this day and age when everybody is suing everbody else at the drop of a hat I still think best practice would be to link all pipes under boiler if just to cover your back,just my opinion don,t know about everyone else.

I guess their could be some boilers that have rubber washers, but generally most boiler connections are brass compression fittings and therefore are continuous metal throughout the fitting. Even with a rubber washer it is generally within a metal screw fitting unless the system is plastic in which case there is no requirement to bond.

oldtimer · Feb 17, 2012

Dannyspark I think the term you are looking for is "electrically and mechanically sound" this was from the old 14th edition when trunking and conduit was used as the main earth and funny enough the scheme providors are now admitting that this is a good earthing system.

Also many years ago it is my understanding that the gas and water was used as a main earth because all the pipework was metal and it was meant to be a good source of an earth until they started to upgrade the networks with plastic pipe hence the loss of "electrically and mechanically sound" and it is because of the use of plastic pipe that people are finding that they dont have an earth any more I was called to a flat were the guy said the gas engineer says I have no earth but I did last year when he checked it ? I asked did the guy downstairs do any work he says yes but what that got to do with it turns out he was getting his earth from the guy through the water pipes bonding until he got plastic put in

Deleted member 9648 · Feb 18, 2012

Dannyspark said:
You have to ask the question as to why we bond the gas/water suppy?

Ultimately what we are trying to acheive is to ensure that enough current will flow under fault conditions to ensure that the protective device operates within the required time among other things.
What you are suggesting is creating a mini TT system on the gas pipework and TT systems by design generally have a high a resistance value compared with TNS or TNCS systems.

I think you are creating a headache for yourself by going along this road as you will need to take a reading from the earth rod and do the relevant calcs to ensure that disconnection can be achieved.

I would suggest that you bite the bullet and tell the customer that you will have to run a 10mm cable from one side of their house to the other because providing you have a standard domestic TNS set up you shouldn't need to do any calcs just use the criteria laid out in your OSG.

With regard to the cross bonding issue with the earth tags being threaded into one another, this is a "Plumbers trick" in fact I would suggest that this was the water board in fact.
In fact it is unnecessary with a modern boiler as the manifold (where all the pipework connects into) is generally made of brass or similar metal and providing the gas and water are bonded then by default the entire plumbing system is bonded (unless their is some bodged plastic within the copper system).

Hope this helps.

And the above post has absolutely nothing to do with the reason for main bonding incoming services.It still amazes me how many electricians dont understand the concept.
Disconnection time is achieved by means of the electrical earthing system only.
Main bonding is to prevent possible potential differnce between the electrical earthing system and incoming services at earth potential (by virtue of being in contact with the general mass of earth) for the duration of a fault until the protective device clears that fault.