Why does my current clamp meter show large current in gas pipe?

[loz2754]

Went to a house this morning to locate a fault causing the RCD in a split load board to trip.
Going through the usual tests, I decided to put my earth leakage clamp meter on the earthing conductor.
Here is where it gets weird: with the main switch in the off position, the meter was reading nearly 3 amps through the earthing conductor!!!
So I decided for a giggle to put the clamp around a nearby gas pipe, and got around 1.7 amps through the gas pipe!!!
Ze was 0.30 ohms on what appears to be a TNC-S. Polarity is fine.
Can anyone explain this please?

 

[telectrix]

I would report it. This could cause issues if anyone ever disconnects that gas pipe to replace the meter etc. Wonder what potential difference you would get between the two sections once disconnected?

get a wet-pants to hold both ends. estimate the effect by the dB level of the scream.

 

[DPG]

get a wet-pants to hold both ends. estimate the effect by the dB level of the scream.

It's probably in the gas regs that!

 

[James]

I have 2 theories

1 supply is tncs I believe

If the combined neutral and earth cable is broken between transformer and some properties the following could happen.
N current from properties downstream of fault can’t flow to transformer directly.
They will then try and find an alternative path, this could be through all customers earth terminals and flowing to real earth via metal pipework buried in the ground.
The 3A you are measuring could be a small part of a huge current with multiple paths via many houses.

Or

2 an underground cable fault is raising the ground voltage around a section of the gas pipe, this is being held at close to zero volts as the pipe is bonded to earth at many houses, however the current would be shared amongst many so you don’t see a voltage rise when disconnecting main earth cable.

I think either scenario would warrant a call from the dno to check it out.

 

[UNG]

Reminds me of one a DNO guy told me recently, homeowner got a plumber out because she was getting very warm water from the cold tap, plumber confirmed that the cold feed was bringing warm water into the house and called United Utilities who then got ENWL involved, it was found that a faulty cable joint in the street adjacent to the water pipe was the cause of the problem
It did make wonder what an electrician would have found in the property

 

[littlespark]

Just fuse the gas pipe.

simples

?

 

[Lister1987]

this can be very dangerous situation especially to other tradespeople like plumbers who may expose themselves.

Dirty dirty feckers ?

 

[Lucien Nunes]

I wouldn't say that current was high enough to imply there is a fault, it sounds more like ordinary CNE current finding parallel paths back to the substation via extraneous metal services as described by @Pretty Mouth above. The resistance of buried metallic services is in the same order of magnitude as that of the cables, so when they are all connected together, currents of the same order of magnitude can flow through them.

 

[Lister1987]

e5 did so videos on this phenomenon we know as Diverted Neutral Current;