Sparks/arc at gas meter

[polesapart]

Some years ago when working in a domestic property whilst disconnecting a gas meter I got sparks between the meter outlet and the pipework.
When I gripped the meter supply and outlet pipes with the meter removed I could feel nothing.
Yes I know I should have put my temporary earth continuity bond between inlet and outlet pipework before disconnecting the meter and yes I was lucky not to blow up meter, self, and property.
My question is this: what exactly was going on? Whenever I've asked electricians this I have received answers like "Fault current" "Anomaly" "Earthing not to standards" even "computers can cause this" These answers may be correct but uninformative.
Obviously there was some kind of (fault) current/potential difference/?capacitance involved but exactly what? What would be the characteristics of such a current that could produce sparks but not a shock detectable to the human body,and under what conditions could this phenomenon be generated down a gas pipe in a house?

 

[westie101]

Read the section referring to NET CURRENTS

http://www.emfs.info/Sources+of+EMFs/distribution/

it's quite common.

Another interesting section is here regarding neutral/earth faults on internal wiring

http://www.emfs.info/Sources+of+EMFs/distribution/Neutral+earth+connections.htm

 

[RF Lighting]

It might be that the voltage present on the pipework was low enough to not give you a shock, but a spark will still be visible even if theres only a few millivolts in the 'circuit' which you are breaking / making.

 

[plugwash]

The problem is that for some crazy reason the wiring regs specify bonding on the consumers side of the meter. So when you disconnect the meter from the pipework you are effectively disconnecting the bonding from the gas service pipework. If there is any potential difference between the gas pipes and the installation earth then you can get sparks.

There are many reasons an installations earth can be at a slightly different potential from pipework coming into your house but the biggest one is the use of combined neutral and earth cores in the electricity suppliers wiring.

I wouldn't think an explosion is likely, generally gas only explodes when you first get a good mixture of it with air THEN ignite it. If you just light the end of an open gas pipe you will "just" get a jet of flame...

 

[polesapart]

Thanks for all the above replies; I think that the penny has dropped (ish).

In 2005 with the introduction of Part P I went on a C&G ?16th edition regulations course with the intention of being able to continue wiring my own (wet) heating systems. I got the paper but five days in the company of lifetime electricians brought home to me the depths of my ignorance of matters electrical: I have since always employed a qualified sparks instead.

As RF wisely puts it, tea is for mugs.