No main bonding seen but good continuity.

[HappyHippyDad]

Evening..

I have just completed an EICR. The incoming gas pipe has been hidden behind kitchen units. I have dismantled the plinths, emptied the cupboards and used my inspection camera all to no avail. I cannot see any main bonding.

I can just get my hand through an inspection hole cut in the back of one unit and reach the incoming gas to get a crocodile clip on to it. I get a reading of 0.05Ω using a wander lead back to the MET.

In the CU there is a 10mm bonding cable which I have identified for the water, then there are 2 unidentified 6mm earthing/bonding conductors.

I have to admit I'm at a bit of a loss as to which code to give this? No main bonding is a C2, but with a reading of 0.05Ω!!?? The CU is approx 8m away from incoming gas pipe.

Any suggestions? Running a new 10mm would mean taking up laminate and kitchen floor tiles or making lots of holes in the ceiling which seems a bit crazy given such a low continuity reading which leads me to think it is bonded somewhere behind the units.

 

[davesparks]

The amount of work required to rectify is irrelevant.

Is the gas pipe an extraneous conductive part?

 

[Dave OCD]

Just a thought HHD, is there an external meter box ? If so the gas bond might be in there, otherwise a boiler will often give automatic continuity between all connected copper pipework ?

 

[davesparks]

It's almost guaranteed that the current reading is at least partially via the gas appliances.

Testing the gas service for being extraneous is in my opinion essential to resolving this.
Then if it is extraneous introducing the Unidentified bonds in to the test to establish if they connect to the pipework will help

 

[bigspark17]

An earth connection must be accesible for regular inspection and testing, your reading means nothing as 0.05 ohms is only relevant to the equapotential conductor not the parralel reading of the pipes back to met via appliances, c2 imo from the info in your post.

 

[ruston]

And on your inspection list of supply characteristics and earthing arrangements, 'connection /continuity verified'

 

[davesparks]

An earth connection must be accesible for regular inspection and testing, your reading means nothing as 0.05 ohms is only relevant to the equapotential conductor not the parralel reading of the pipes back to met via appliances, c2 imo from the info in your post.

What is the potential danger that you have identified?

His reading is 0.05 including all of the parallel paths so how can you say that they are not relevant?

 

[HappyHippyDad]

I think I may have found a solution. The water bonding runs very close by and actually goes past the incoming gas, there is a fair bit of excess from the 10mm conductor, so I could divert it to the gas on its way to the incoming water pipe (keeping it continuous). I would have to make the inspection hole a fair bit bigger, but a small price to pay compared to taking up laminate.

What would you code this Dave? From your initial posts it seems as though you would class it as work that needs carrying out, yet your last post 'hints' towards this not being the case.

What is the potential danger that you have identified?

His reading is 0.05 including all of the parallel paths so how can you say that they are not relevant?

 

[topquark]

One other minor comment, can't see mention of the type of earth sys; if it's TNC-S then those 6mm should be min 10mm if indeed they are main bonding conductors.

 

[davesparks]

I think I may have found a solution. The water bonding runs very close by and actually goes past the incoming gas, there is a fair bit of excess from the 10mm conductor, so I could divert it to the gas on its way to the incoming water pipe. I would have to make the inspection hole a fair bit bigger, but a small price to pay compared to taking up laminate.

What would you code this Dave? From your initial posts it seems as though you would class it as work that needs carrying out, yet your last post 'hints' towards this not being the case.

You haven't told us what the result of testing the gas pipe for being an extraneous part is yet, without that information I can't make a decision on coding it.

It is very hard to know exactly what I'd do without actually seeing the installation and being able to see all of the little pointers that allow you to decipher the story of how it got to being what it is now.
I'd be looking at the 6mm bonds to see if they look like they could be the original gas and water bonds with the 10mm being a later addition, and if 6mm is right for the age of the original installation.

Also I'd be looking at the water main and gas supply pipe to assist with dating the installation, and also look at whether it's a metallic or PE gas service pipe.

 

[HappyHippyDad]

I have not tested to see if extraneous. I admit I have completely assumed it must be extraneous as its a metal pipe entering the house form a semi buried meter which has a metal supply pipe going into the ground. In addition how would you test to see if extraneous given the following.. Its tncs so even if I disconnected main earth to test would It not still be connected to other property's pipework? Also, in order to test to see if extraneous would I not have to find out out if the gas pipework is connected to any other extraneous parts (water etc) and disconnect from those?

 

[kenny7askew]

I have not tested to see if extraneous. I admit I have completely assumed it must be extraneous as its a metal pipe entering the house form a semi buried meter which has a metal supply pipe going into the ground. In addition how would you test to see if extraneous? Its tncs so even if I disconnected main earth to test would It not still be connected to other property's pipework?

exactly,i would do what you said in post 8

 

[davesparks]

I have not tested to see if extraneous. I admit I have completely assumed it must be extraneous as its a metal pipe entering the house form a semi buried meter which has a metal supply pipe going into the ground. In addition how would you test to see if extraneous given the following.. Its tncs so even if I disconnected main earth to test would It not still be connected to other property's pipework? Also, in order to test to see if extraneous would I not have to find out out if the gas pipework is connected to any other extraneous parts (water etc) and disconnect from those?

Ok, I don't think I've ever encountered a metal service pipe feeding a semi buried meter, only the yellow plastic with the metal Union/termination on at the joint to the anaconda.
Once upon a time it was a lot easier to work out as the gas board fitted a label specifically telling you that a plastic service pipe was installed.

Yes it is tricky in a TNCS supply, but the test will still give you a result which can help your decision making process. You may get a reading which shows negligible resistance to the TNCS Earth terminal, which as you have said, would indicate that the pipe is continuous metal to other properties. This in itself would confirm a requirement for bonding.

Your point about the gas pipe being connected electrically to the water pipework, usually via the boiler, is a very good one and it is something that I've discussed at great length with a few people.
I also have a concern on the interpretation of the regulation concerning the identification of extraneous parts which i still can't quite settle in my mind.

Is this a 70s/80s property by any chance? If it is then 6mm main bonds would be right for that era and would make me lean towards the two 6mm earths being the original main bonds.

Based on all of the information you've given so far I would make an observation that bonding conductors are present at the MET and testing indicates that the gas pipework has a low resistance connection to the MET but the location of the bonding connection to the pipe is not readily identifiable, also the bonding conductor identified at the MET is undersized according to the current standard. I would give this a C3 with the recommended improvement for safety being the connection of a 10mm bond at an accessible location.

 

[davesparks]

exactly,i would do what you said in post 8

That doesn't help with making the observation on the EICR, unless you are going to do the work free of charge whilst carrying out the EICR?

 

[hightower]

Based on all of the information you've given so far I would make an observation that bonding conductors are present at the MET and testing indicates that the gas pipework has a low resistance connection to the MET but the location of the bonding connection to the pipe is not readily identifiable, also the bonding conductor identified at the MET is undersized according to the current standard. I would give this a C3 with the recommended improvement for safety being the connection of a 10mm bond at an accessible location.

Thanks Dave, very helpful reply - even though it's not my thread. So if I may take this slightly off topic, if you encountered a situation where you were extending a ring or a lighting circuit, and first go to check the main bonding - it exists in the CCU but you can't find where it terminates at the gas side. So you disconnect the gas bonding from the MET and continuity test it with the pipes at the meter - you get 0.05ohms, so surely the pipe is bonded. However, do you carry out the minor works on that install and treat this reading as a good enough indicator that it's bonded, or because it's not available for inspection at the gas pipe do you class it as not good enough and needs new bonding running first?

Thanks,