Difficult Service head

[GMES]

@Lorzor I have deleted the images in your opening post for obvious reasons.

 

[Octopus]

@Lorzor I have deleted the images in your opening post for obvious reasons.

I've just read this whole thread hoping to see them.....................

 

[Dave OCD]

I've just read this whole thread hoping to see them.....................

Me too !

 

[Lorzor]

Oh man, you really missed out. I'm the ultimate badass!

 

[Richard Burns]

Looking at the service head on arrival I would have assumed a (slightly odd) TNCS arrangement.
The earthing conductor (even though in this case it is a gas bond) cable would not normally exit at that point, but no reason for it not to do so.
On measuring Zs at the consumer unit and getting a 0.11 ohm reading I would initially assume I was correct.
On attempting to measure Ze and checking the bonding arrangements I would then have been confused on finding the conductor from the service head was solely terminated onto the metal gas pipe.
On removing this conductor from the gas bond (and disconnecting the other bonding) I would then expect the Ze reading to be significantly higher since I would expect that the gas pipe was being used as the means of connecting the means of earthing to the installation (not permitted).

Because you have disconnected the bonding and got a Ze reading of 0.11 ohms there must be another means of earthing the installation, either the conductor from the service head is split in two at some point and goes off to the consumer unit and to the gas or there is another unseen conductor earthing the consumer unit.
If there are any other 6-16mm² green and yellow conductors in the consumer unit, that are not identified bonding, then I would be attempting to trace where they go and see if there is another reason for the low impedance.

 

[Lorzor]

Looking at the service head on arrival I would have assumed a (slightly odd) TNCS arrangement.
The earthing conductor (even though in this case it is a gas bond) cable would not normally exit at that point, but no reason for it not to do so.
On measuring Zs at the consumer unit and getting a 0.11 ohm reading I would initially assume I was correct.
On attempting to measure Ze and checking the bonding arrangements I would then have been confused on finding the conductor from the service head was solely terminated onto the metal gas pipe.
On removing this conductor from the gas bond (and disconnecting the other bonding) I would then expect the Ze reading to be significantly higher since I would expect that the gas pipe was being used as the means of connecting the means of earthing to the installation (not permitted).

Because you have disconnected the bonding and got a Ze reading of 0.11 ohms there must be another means of earthing the installation, either the conductor from the service head is split in two at some point and goes off to the consumer unit and to the gas or there is another unseen conductor earthing the consumer unit.
If there are any other 6-16mm² green and yellow conductors in the consumer unit, that are not identified bonding, then I would be attempting to trace where they go and see if there is another reason for the low impedance.

That was my guess, I'm going to attempt to find another method of earthing. It seems there may be quite a large cavity behind that service head, so it may be behind there. Don't worry, I won't dismantle it to get behind!

 

[weevilward]

Is the house semi-detached or maybe terraced? I've been in a semi detached TT house with Ze (measured through the rod, main earth disconnected from CU) of 100ish ohms, but Ze measured at the CU with everything connected it was right down to 0.20 ish. Next door had been converted to PME and there was a metallic path between the properties, I think through the plumbing systems, boiler CPC etc. So even with the means of earthing disconnected in this house, it appeared that Ze was stil 0.20 ohms.

 

[weevilward]

It might be that your place isn't actually earthed, but appears to be earthed from an adjoining property?

 

[weevilward]

P.S. I didn't see the OP photos so might be barking up the wrong tree...