High Ze with Low Zs, and Location of Water Bonding.

[acvc]

1.
Doing Ze today and getting weird results: 0.97, 1.10, 1.21. (Using Megger 1552).

As I was doing the test, there was a definite arcing type of clicky sound each time down in the region of the the mains head. I couldn't see down there as I was testing as my arms weren't long enough.

However, Zs values on the socket ring were fine, in the region of 0.32 to 0.64 ohm.

How can this be???

I thought it was TN-S, but I'm beginning wonder if there's any earthing facility at all ..... (but there must be).

The main earth conductor (16mm) came from a clamp around the steel conduit within which the L and N from the mains head went to the CU. There was also a strand of steel wire maybe 4mm in diameter from the mains incomer sheath to this clamp. As well as this, the reason I assumed it was TN-S was the absence of an earthing block in the neutral, and the fact that the main earth conductor didn't go looking for a rod, but went to that clamp. Is it TN-S?

2.
And here's another question! There was no water or gas bonding in the house when I got there. The water comes in at the back of the house below the kitchen sink in a tiled (floor) kitchen. To get a 10mm earth from there to the front where the CU is would be cause carnage.

This house is next door to mine in a row of terraced houses. As the two houses share an incoming water feed which comes into mine, splits, then goes through the wall into next door (the house I'm working in), I have taken the liberty of running the 10mm water bonding through the wall to mine and placing the bonding clamp on the incomer in my side. I think there might be a Reg that says this isn't allowed, but is it ok if the water feed is shared between the two houses?

Sorry for the long post, but this has gone from three extra sockets to this! And I was hoping to use it for my NIC annual inspection next week.

If you've got this far .....Thanks for reading it.

 

[Johno]

It is TN-S, to get a Ze reading you need to disconnect the wire from the sheath from the clamp and test.

I had it recently where the Ze in a TN-S was over 8 ohms and told customer to ring supplier, and they came out immediately and sorted it

 

[Johno]

and I think you already know the answer to the water main question

 

[acvc]

Thanks Johno.

I'm right up against it here. My own fault, I know. This was meant to be a straightforward job - add three sockets, put in 30mA RCD, inspect-test-certify, get NIC Inspector in Wednesday and hey presto.

Now though it's the classic can of worms! No bonding at all and dodgy main earth connection. The reason I didn't do a reccy was a)because it's next door and b)because it has an extension put on a few years ago and I assumed the electrics would have been inspected then. Lesson learnt.

I'm going through the BigRedBook with a fine toothcomb now for info about location of main bonding connection. There's nothing in 411.3.1.2, nor is there anythng in Chapter 54.

Any clues chaps?

 

[Tester Steve]

Hi,

Services bonding should preferebly be within 600mm from where it enters the property, or where practical before any branches. As Johno has said, you will need to do this in the property.

Steve