Grounding advice on older property

Stubby · Feb 24, 2019

Hi, I’ve just been to look at a job to add a socket in a ex-mod (1960ish) domestic property. The cables are singles pulled through metal conduit in between the ground and first floor. The problem is that the sockets have no CPC conductor in the back box so I ‘assumed’ that the CPC was fed through the metal conduit. I went back to the Consumer Unit to check this and the only earth that I could see was from the gas meter to the CCU. At this point alarm bells started ringing that the property is not grounded! I then thought that it maybe a TT system but there doesn’t seem to be a ground spike anywhere around the property. Could there be an ‘internal’ spike when the house was built?
I’m surprised as the CCU has been changed and smart meters have been fitted to this property so I’m beginning to doubt myself that they spotted something that I haven’t... any help would be great as I’m starting to think that this property isn’t safe.
Thanks in advance,

[ElectriciansForums.net] Grounding advice on older property

SparkyChick · Feb 24, 2019

Have you looked inside the consumer unit to check whether or not the conduit is connected to earth internally? I suspect the answer is no given there is a section of plastic flexible conduit linking one section to the board.

That issue aside, there doesn't appear to be any earthing present, so you're going to need to do something about that, either check with the DNO to see if PME is available or install an earth rod.

Overall, looks like you could have a bit of work there.

ChrisElectrical88 · Feb 24, 2019

That CCU change must be over 20 years old.

freddo · Feb 24, 2019

What a rubbish install, the person that changed the consumer unit should be ashamed.

davesparks · Feb 24, 2019

The steel conduit is the CPC for the circuits, the problem is that there doesn't appear to be any incoming earth or proper connection of the conduits at the CU.

ChrisElectrical88 · Feb 24, 2019

You got any pictures inside the board?

telectrix · Feb 24, 2019

a Ze measurement would have confirmed presence of earthing( or not).

telectrix · Feb 24, 2019

ChrisElectrical88 said:
You got any pictures inside the board?

you mean of his wife, naked?

Wilko · Feb 24, 2019

Hi - perhaps get the owner to call up DNO for a safety check (SSE will do that). Then you can work out next steps, but no work on outlets at present

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My Sunday morning thought is perhaps historically it was TT but they've left out the up front RCD. And the rod. And the conduit continuity. If it is as it looks, then I think it's not safe. A kettle fault to earth may liven up any external conductive parts, for example.

Strima · Feb 24, 2019

Ex MOD property? Installation done by the lowest bidder then maintained by an even lower bidder.

Stubby · Feb 24, 2019

davesparks said:
The steel conduit is the CPC for the circuits, the problem is that there doesn't appear to be any incoming earth or proper connection of the conduits at the CU.

I agree, I wouldn’t think there is any link inside!

Stubby · Feb 24, 2019

Strima said:
Ex MOD property? Installation done by the lowest bidder then maintained by an even lower bidder.

Spot on!!

Stubby · Feb 24, 2019

ChrisElectrical88 said:
You got any pictures inside the board?

Unfortunately not! I wish now that I’d undone the cover but, to be honest, I was too scared as to what I might find!!

SparkyChick · Feb 24, 2019

Stubby said:
Unfortunately not! I wish now that I’d undone the cover but, to be honest, I was too scared as to what I might find!!

You may have found that the conduits are adequately connected to earth (which could be verified with a Zs test) and that in fact there is an earthing conductor exiting through the rear of the board to an old earth rod somewhere in the fabric of the building (which could be verified with a Ze reading).

If in doubt, take the cover off and check it out

If it's too scary you can always put it back on, but remember there are some things you'll wish you could unsee

Do you have a photo of the service head and service cable? It could be a TN-S earth which has been damaged/removed by someone. There does appear to be a little tag of something on the service cable.

Cid · Feb 24, 2019

Confirm with the DNO what type of earthing system they provide with this property. It could be something small as previous installer forgetting to connect the earth cable to the cut out.