gas pipe sparking!!

[Edd]

Sent to a property where there had been a small fire! They have had a new 17th CU fitted a lighting rewire and all Bonding brought up to Regs.
I get a call saying the plumber has gone to connect the gas meter to the incoming pipe and a spark was seen.
I test between MET and incoming gas pipe and show 10V. Ze is 0.23 and all seems OK. Thinking its just the gas fitter over reacting and thinking it just requires bonding so everything is the same potential, the little old dear shows me this.
After being shown the picture below I took a cable from the MET to the incoming gas and touching on the pipe there was a substantial spark almost like sticking a wire across a small car battery. I pulled the service fuse and still there was 10V and a big spark was created. At this point I was at a loss the fault was external and I passed it on to the Gas and DNO. Any Ideas?

 

[Knobhead]

Looks like there's a N→E fault and a dodgy neutral somewhere.

 

[Edd]

Thanks Tony, just for people's intrest, it's a 1920's mid terrace house with underground mains, the Earth strap to the sheath is a nice new braded type. And as for pulling the main service fuse, I was at a loss, so why not pull it? I may have missed something really stupid. But really this is one of the reasons I stoped posting here..

You post an interesting fault about a fire and sparking earth, and all someone's intreste in is that I pulled the service fuse... Really helpful in the question I was asking NOT!!!

 

[Deleted member 9648]

Looks like there's a N→E fault and a dodgy neutral somewhere.

I already said that and didnt get a flickin thanks!.....:mad2:....

 

[Edd]

I already said that and didnt get a flickin thanks!.....:mad2:....

sorry, I've had many N-E faults and loose N on PME systems.. Just lost me with a TNS system and supply to property off (OMG I pulled the fuse as well) and still got a low voltage but high current fault.. I'm still trying to picture Tony's explanation in my head, but I'm getting there...
Thanks
Edd

 

[Newbyspark]

Saw the same thing the other week. Loose bonding connection on gas was sparking, over how ever long it was doing it it melted through gas pipe and ignited gas. Dno came out and even with main fuse out it was still sparking. They were scratching their heads a lot. In the end they think it was a fault in another house but as this house had probably better bonding, the fault was coming down this bonding. Probably would never known if the connection hadn't been loose. No one hurt, but very lucky

 

[R G]

Seen this sort of thing a couple of times on the DNO I worked for , the thing is there are so many new supplies installed of a TNS network and its usually a TNCS supply fed to new properties or even conversions in some instances , and then a lost neutral in one of the cable joints and then the bonding becomes live and transmits it through another place through the pipework external to the property , Ive seen it where the bonding wire had actually melted....

 

[davesparks]

Thanks Tony, just for people's intrest, it's a 1920's mid terrace house with underground mains, the Earth strap to the sheath is a nice new braded type. And as for pulling the main service fuse, I was at a loss, so why not pull it? I may have missed something really stupid. But really this is one of the reasons I stoped posting here..

You post an interesting fault about a fire and sparking earth, and all someone's intreste in is that I pulled the service fuse... Really helpful in the question I was asking NOT!!!

I am not criticising the act of pulling the service fuse, I have no issue with cutting seals and doing the same.

I am interested to know what logical thought process brought you to the conclusion that doing so was going to assist in this situation.
I cannot currently see the logic behind this and would like to learn from you what this is. It may be that there is something I do not yet understand which may help me in the future.

Is this not one of the reasons forums like this exist?

 

[Knobhead]

Edd, all you can do now as if I suspect the fault is external to the house is contact the DNO. Which I believe you have done.

If you can, be there when they attend.
The fault on my own house was a bloody good learning exercise for me as I was about a year out of my time. I’d almost no experience of domestic wiring systems. (40 years later I still haven’t got a great deal of experience for that matter.)

As for pulling the service fuse, I can’t see what the hell that has to do with this fault. The NWEB senior engineer that attended the above fault, his only comment was “you don’t believe in seals do you!” He became a good friend and helped me out with some of my projects later on.

Something to bear in mind, this fault won’t just be confined to the house in question.

 

[Edd]

I am not criticising the act of pulling the service fuse, I have no issue with cutting seals and doing the same.

I am interested to know what logical thought process brought you to the conclusion that doing so was going to assist in this situation.
I cannot currently see the logic behind this and would like to learn from you what this is. It may be that there is something I do not yet understand which may help me in the future.

Is this not one of the reasons forums like this exist?

My logical conclusion was I had tried everything else and the fault remained. I understand the problems with PME Systems and loose neutrals but had never seen it with a TNS System. When out of ideas try anything..... Oh and I'm techniquely allowed to pull the fuse as I used to sub to the EEB and have a nice little certificate...

 

[Engineer54]

There are many original TN-S supplies that are now serving both TN-S and TNC-S. Parts of the original cables lead sheathing having corroded away over time, or due to cable passing through aggressive sections of soil etc....

So it is more than feasible that one or more of this row of old terraced houses having a TNC-S supply, where a fault is being passed on to the gas/water supply services via main bonding cables. Something for the DNO to sort out, if you have proved to yourself that there is no fault originating from the property you are working in!!