Question on supply cable Earthing

[MikeKing]

Morning! Hi to briefly introduce myself, I’ve done my 2365 L2&3 and hoping to get enough money together to do my AM2 this year. I also have my 17th and am registered with Stroma only since last year. I’m also a long time reader of the forums, learnt absolutely tonnes.

I’ve a question I hope you can help with. I’m upgrading some of the electrics at my brothers place, getting rid of old rewireable fuseboard and putting in a new consumer unit, new ring final for his ground floor. However, when I went to check the bonding to the utilities, there wasn’t any at all. I’ve checked both supply pipes where they come into the building and at the stop cocks. I thought maybe I just couldn’t find them, but there’s nothing in the MET apart from cpc’s from the 5 circuits and a 6mm earthing conductor to an earth block next to the supply cable. So obviously I’m installing bonding now as well, and here’s my question.

It’s a TN-S system, with a couple - literally two strands of armour that seemed to have been unravelled from the supply cable when it was installed and connected to the same earth block. I can post a photo in a few hours if needed.

My gut is screaming out that there’s no way those two strands are capable of carrying any decent PFC?

Everything I’ve read says it’s the DNO responsibility to sort this, but I’ve also read that if you call them they’ll just say stick a Tenby clip on it - which I don’t think is right either as it's likely to come loose.

So am I being paranoid about the armour earthing and where do I stand when speaking to the DNO?

Thanks in advance! Mike

 

[Pete999]

Mike the 6mm2 cable you talk of, where is it connected? and the cpcs from the circuits you describe as connected to the MET. Is the MET you speak the earth bar in the CU? I only ask because it's very that someone has taken the cpcs out of the CU and connected them to an external MET. Sorry if this sounds confusing, perhaps some photos of the set up may clear things up a bit.

 

[MikeKing]

Yep that’s exactly it. The 5 cpc’s into an MET in the old Wylex rewireable fuseboard. And a 6mm connection to an external earth block, of which the armour to the supply cable is connected.

Yep will get photos in an hour or so.

 

[polo1]

If you’re not happy with the incoming earth, then contact the local DNO - if they provided the earth, then they have a duty to maintain it at no cost to the home owner. They may upgrade to tnc-s.

 

[Pete999]

Yep that’s exactly it. The 5 cpc’s into an MET in the old Wylex rewireable fuseboard. And a 6mm connection to an external earth block, of which the armour to the supply cable is connected.

Yep will get photos in an hour or so.

Thought as much, sounds like you need to get in touch with the DNO.

 

[MikeKing]

Mike the 6mm2 cable you talk of, where is it connected? and the cpcs from the circuits you describe as connected to the MET. Is the MET you speak the earth bar in the CU? I only ask because it's very that someone has taken the cpcs out of the CU and connected them to an external MET. Sorry if this sounds confusing, perhaps some photos of the set up may clear things up a bit.

Photo added for a bit of clarity

 

[Pete999]

Photo added for a bit of clarity

View attachment 41107

Is that the 6mm coming from the U/G cable? going to the MET?

 

[MikeKing]

Is that the 6mm coming from the U/G cable? going to the MET?

Hope I haven’t caused more confusion, my brother sent me the picture before I started, so I had it on my phone and I’ve just cropped it.

The connection you can see between the supply cable and the earth block looks like it’s just a couple of strands of the armour.

The 6mm connection to the board is helpfully just out of shot and behind that meter tails and runs behind the wooden board the meter is mounted on, so it’s just out of view in that picture.

 

[Pete999]

Hope I haven’t caused more confusion, my brother sent me the picture before I started, so I had it on my phone and I’ve just cropped it.

The connection you can see between the supply cable and the earth block looks like it’s just a couple of strands of the armour.

The 6mm connection to the board is helpfully just out of shot and behind that meter tails and runs behind the wooden board the meter is mounted on, so it’s just out of view in that picture.

Have you taken any Ze readings? best all round to get the DNO involved, if the Ze is not up to scratch.

 

[telectrix]

that looks like it's PILC supply cable. the earth connection is sweated onto the lead sheath. as was done donkeys years ago. get a Ze and PEFC readings. you'll find that it's probably adequate. then sort out your bonding.

 

[MikeKing]

Yeah Ze was 0.21 ohms so I was quite impressed. I might give them a bell and see what they say though, but thanks so much for the replies!

 

[Pete999]

that looks like it's PILC supply cable. the earth connection is sweated onto the lead sheath. as was done donkeys years ago. get a Ze and PEFC readings. you'll find that it's probably adequate. then sort out your bonding.

Deleted

 

[telectrix]

@ 0.21 ohms, that gives a pefc of appeox 1kA. adiabatic tells me that 2.5mm is adequate for a MEC. so that tail off the lead sheath will comply.

seen quite a few like that, been in for years. never seen one melted .

 

[MikeKing]

Thanks all - appreciated

 

[davesparks]

That’s not a few strands of the armour, it’s a tinned copper braid.