TT or PME

[aliensbrains]

Just been to look at a job and found this. It's an overhead supply so could be pme at the post but no earth back to the cutout and (although admittedly i didn't have much time to have a proper look) I didn't spot a rod.

I'm thinking advise the customer to get the dno to come and have a look and fit an isolator while they're at it.

Any thoughts?

Thanks!

 

[mainline]

Just been to look at a job and found this. It's an overhead supply so could be pme at the post but no earth back to the cutout and (although admittedly i didn't have much time to have a proper look) I didn't spot a rod.

I'm thinking advise the customer to get the dno to come and have a look and fit an isolator while they're at it.

Any thoughts?

Thanks!

View attachment 119116

I think one of the first things would have been a Zs and rcd test, it would have taken a few minutes.

 

[aliensbrains]

I think one of the first things would have been a Zs and rcd test, it would have taken a few minutes.

Agree but customer hasn't exchanged yet and it's occupied. I couldn't do any testing during this visit.
When they exchange I will try to get back and test but that doesn't help me in the meantime.

 

[James]

The label on the incomer states that it is PME.

however,
in the absence of any visible earthing cables, then it must be assumed that the installation is one of the following.

1. TT with an earth cable hidden from view
2. no earth connected
3. a dodgy PME link inside the DB.

as the label states PME then in all honesty, the cost of fixing the earthing is negligible anyway.

 

[mainline]

Agree but customer hasn't exchanged yet and it's occupied. I couldn't do any testing during this visit.
When they exchange I will try to get back and test but that doesn't help me in the meantime.

What was the point in you going there ? If you didn't have 20 seconds of time to even do a quick Zs.

 

[Pretty Mouth]

Agree but customer hasn't exchanged yet and it's occupied. I couldn't do any testing during this visit.
When they exchange I will try to get back and test but that doesn't help me in the meantime.

It's not your customer's installation yet, and as you can't carry out any testing, then I don't see as there's any more you can do. Report your suspicions to your customer, and suggest they have an EICR carried out at the earliest opportunity.

 

[James]

Agree but customer hasn't exchanged yet and it's occupied. I couldn't do any testing during this visit.
When they exchange I will try to get back and test but that doesn't help me in the meantime.

If i was purchasing a property and organised with the seller to allow access for an electrical report to be done,
I would be wary and disappointed that the engineer was prevented from doing the job correctly.

a quick visual of the board internals and 10 minutes of sticking your meter probes in and you would be able to give a proper report. albeit with some restrictions.

 

[Tom256]

as the label states PME then in all honesty, the cost of fixing the earthing is negligible anyway.

Not necessarily. You need the history on this which the DNO can provide.
Engineering Recommendation G12 allows a DNO to refuse connection to the supply Neutral if the DNO considers it inappropriate for reasons of safety. One such reason could be a TN-C-S Earthing non-compliance against BS 7671. Could be no insulating section in a metal gas supply pipe and so on.

It could be if rural, single premises, a PNB at the pole transformer creating the TN-C-S from the transformer to customers intake (?). Regardless, connection can be refused if it is not considered by the DNO safe to do so.

Looking at the top of the consumer unit I can see what would be 3 x Earth conductors which could suggest a possible TT arrangment in place (?)

 

[Tom256]

If i was purchasing a property and organised with the seller to allow access for an electrical report to be done,
I would be wary and disappointed that the engineer was prevented from doing the job correctly.

Yes indeed James.
Side topic - apologies - Be worth checking if those BS 3871's are suitable for Safe Isolation. Not all are. Example: The Mk1 Merlins as shown (picture) and recognised by the toggle width cannot be confirmed safe by Schneider for use in Safe Isolation.

 

[aliensbrains]

Not necessarily. You need the history on this which the DNO can provide.
Engineering Recommendation G12 allows a DNO to refuse connection to the supply Neutral if the DNO considers it inappropriate for reasons of safety. One such reason could be a TN-C-S Earthing non-compliance against BS 7671. Could be no insulating section in a metal gas supply pipe and so on.

It could be if rural, single premises, a PNB at the pole transformer creating the TN-C-S from the transformer to customers intake (?). Regardless, connection can be refused if it is not considered by the DNO safe to do so.

Looking at the top of the consumer unit I can see what would be 3 x Earth conductors which could suggest a possible TT arrangment in place (?)

It's not rural, it's in a town so I'm hopeful this is just an old TT system but I couldn't spot the rod as it was dark. I think the DNO have stuck PME notices on these cutouts as it's PME'd at the poles.

I think I'll stick to my original plan and let the customer know what I've spotted and advise they call the DNO out on completion to confirm PME and install an isolator. I can then get in and have a proper look.

 

[westward10]

That traffolyte label glued to the service head is the same as those screwed to the wooden support poles.

 

[aliensbrains]

I now have a bit of update on this one.

The customer completed this week so found an hour to go back and test. Generally it all tested out well. Maybe too well in some ways...

Those 3 10mm earth cables are bonding and main supply earth... I assumed it would be a rod under the floorboards but measured 0.27 Ze. Now I'm confused as to where it's PME'd and unfortunately didn't have time to trace the cable.

As was the original plan, the customer has raised an enquiry with the DNO on the basis there's a PME sticker but no earth at the cutout.We haven't mentioned the Ze reading.

 

[Tom256]

Just seen in your post of the 19th of December

I think the DNO have stuck PME notices on these cutouts as it's PME'd at the poles

In my post prior to yours on the 19th I mentioned the possibility of a PNB external at a pole transformer is that indeed the case?
The neutral - earth link need not be at the cutout. A point made often when what presents as TN-S is not.

 

[buzzlightyear]

No PME earths to the to the main tails cut out ,so your testing 27 ohms
so you saying earth rod under flooring ,with out confirmation then what if you are doing a EICR.

 

[Tom256]

Confirm the arrangment as there can be several variations even with PNB.
From that sure would be nice to know if the DNO have offered / provided an Earth terminal