Consumer Unit Replacement issue

[P&Q]

Hi Guys,

I got a little problem that’s a bit confusing and I’d appreciate your help on it.

Firstly, from the picture I have attached, what type of earthing system do you reckon this is? There’s an individual cable coming from the ground going into a metal trunking as you can see, which looks like TNS, however on the existing CU the main earth and neutral have been combined which looks like TNC-S, there is no relevant paper work available at all, I called the DNO and they suggested sending out an electrician for £180 + VAT to tell me what the earthing system is, apparently they have no records of what the system is in this building – is that usual?

This picture is the main supply in a building of six flats. I’m trying to replace the consumer unit in one of the flats on the second floor. There is over 10m long of 16mm tails. The max demand on the CU in this flat is 66.4A, the main cut out fuse is a 60A, so by my calculations the cut out fuse and tails need upgrading but the problem is, upgrading the tails is a big job going from ground floor up to the second floor.

So, I was wondering if you guys with more experience had any solutions that could help me like always?

Thank you in advance for your help.

 

[superspark]

One of the reasons that I asked is, this is not something that I do on a regular basis or that I am fully up to speed with.
I looked at the picture and did not see any link to the main incoming head, regarding the PME, just the lug, bolted to the tape, unless you cant see it, but normally, you would see the bolt sticking out.
I have done a few small blocks of flat, with Ryfields, and they have never been like this, with a rod, which is from the Ryfield . They have always picked up the PME from the Head, No Rod.
I am a great believer that you learn something new all the time.

Thanks

 

[TPES]

Didn't know you could get DNO supplied PME rod..

So although there is an earth rod in the ground and the earth is not supplied by the DNO is this not looked at as a TT system? The fact that this earth is now combined with the neutral now makes it PME (TNCS) right?

 

[Engineer54]

Yes you can have DNO supplied earth rod, granted It's not a common occurance, and depends on many factors, isolated locations, and supply configurations being two of them. In this particular instance it's not sure if the black coloured earth cable does come from an earth electrode or if it's connected to the DNO 's cable sheath/armouring below the FFL. ....Then we have the CNE connection within the ryefield panel just to confuse matters further. I'd personally drag the DNO out, to verify exactly what earthing system they have at this installation.


No, ....earthing a DNO neutral at the installation with an earth electrode doesn't make a PME or a TNC-S supply. In order to comply with PME, or even a TNC-S system the DNO supply neutral MUST be earthed at numerous points along it's overall length. True PME requiring substantially more neutral earth points than a bog standard TNC-S....

 

[superspark]

SO not being sure if the Black earth cable is connected to a Rod TT, or Sheath TNS, it is still alright to leave the link in the Ryfield CNE.

If any or either of these scenarios, are in fact what is being used, What then would go on the Cert !!

or as you say possibley get them out to confirm, by drawings, reports, and testing.

 

[Engineer54]

SO not being sure if the Black earth cable is connected to a Rod TT, or Sheath TNS, it is still alright to leave the link in the Ryfield CNE.

If any or either of these scenarios, are in fact what is being used, What then would go on the Cert !!

or as you say possibley get them out to confirm, by drawings, reports, and testing.

NO it wouldn't be alright to leave the link in place.
You could do some tests, to give a better idea as to what this DNO earth system is, or not as the case maybe. But as i say, the only sure way is guidance from the DNO. They know there network layouts far better than anyone else in that locations area...