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TNS Hybrid with PNB strap

SIGINT

Firstly I’d like to say, thank you for taking the time out of your day to reply!

Information about the property and installation:

2 core Live and neutral most likely 25mm2 because it’s protected by an 80A fuse PILC or PILS, looped supply, Semi detached 1968 build.

I’ve pretty much modernised everything in the property. Full Type A RCBO setup with CPN Cudis type 1+2 surge protection.

I’ve also installed an Isolator switch with an SPD too! Garo type 2 spec.

During my examinations and also bringing in my sparky. We’ve discovered that the system is no longer a proper TNS system. Essentially what’s happened from observation is that the lead sheath of the supply has lost its Earth. Most likely because of degradation and lifespan 40-50 years (BS6480) The system is now a hybrid of some sorts with a mechanical neutral bond to the sheath of the looped supply then wired to the MET terminal Earth block. There is also a tinned Earth CPC nave green that goes underneath somewhere I am assuming it’s an Earth rod…because of the tinned Earth copper configuration and the cable being dug deep down and no way to access it? The cutout also mimics 5-10 second buzzing/arching noises and then disappears?

I’ve contacted the DNO 4 times. First they said it’s “fine” 2nd attempt they just changed the meter tails that goes from the cutout to the meter. 3rd they sent two guys who only did a visual inspection, and I noticed both glared at each other? But didn’t comment? Like they were hiding something? (I could also be mistaken) this might sound picky or fussy or what not but…I don’t feel safe if I am being honest….I feel worried… they are refusing to replace the old PILC/PILS cable…

I don’t know what to do? I just brought this house? And I wish I did an EICR inspection before I brought it. The sparky lad said it would have most likely failed an EICR inspection because of the sheath bonding…

  • in reply to AJJewsbury

    When the DNO technician came, one the first attempt. He removed the neutral cover of the cutout. I noticed two neutrals connected in There’s only room for two connections inside the cutout of the neutral brass terminal. Since it’s a looped supply neighbours and mine have consumed both screw terminals. So from what I’ve gathered they must of realised they can’t connect an earth to the brass terminal because of the looped supply. 

    And what they’ve done is connected an Neutral to Earth bond using an mechanical connection to both of the sheaths of the looped and attached an 4/6mm2 neutral and earth “pine green tinned copper” and wired it back to the MET like a makeshift fix or TNCS conversion?

    Thats what I’ve gathered from seeing him remove the neutral cover to replace the meter tails from the cutout side. But then again it makes an strange buzzing sound Low frequency arc like sound for 5-10 seconds then disappears… but like I’ve mentioned above I’ve had them out to the property 4x times and each time they don’t seem to be interested or wanting to fix or modernise their equipment. 

    I do understand from a financial point of view probably cost them more than £10,000 to replace the PILC/PILS with an SNE Waveform or CNE concentric cable. It will eventually need to be replaced…Luckily I don’t have an electrical car or EV or Solar stuff…

  • in reply to SIGINT
    SIGINT said:
    And what they’ve done is connected an Neutral to Earth bond using an mechanical connection to both of the sheaths of the looped and attached an 4/6mm2 neutral and earth “pine green tinned copper” and wired it back to the MET like a makeshift fix or TNCS conversion?

    Did you see them do it? That earthing conductor looks very old.

  • in reply to AJJewsbury

    I see what you mean. So if it looks like TN-C-S, it could be TN-S; and if it looks like TN-S, there may still be a link nearby. Rolling eyes

  • in reply to SIGINT

    And what they’ve done is connected an Neutral to Earth bond using an mechanical connection to both of the sheaths of the looped and attached an 4/6mm2 neutral and earth “pine green tinned copper” and wired it back to the MET like a makeshift fix or TNCS conversion?

    I'm probably being daft. but I'm still not seeing a link from your MET to the supply N ... (usually there are room for two outgoing Ns at the top - so they could perhaps have used one of those?) Might be they talked about adding a N-PE link but in the end just improved the straight PE connections?

        - Andy.

  • in reply to Chris Pearson

    its better than that - quite often the neighours don't necessarily pay , or dont pay full whack at least,  being the end of loop, its not work that is their fault,  but of course once the supplies are  split it makes a dedicated line for each of you.

    These DNOs do unlooping for free

    https://www.enwl.co.uk/about-us/networkinvestment/unlooping/

    https://www.spenergynetworks.co.uk/pages/planned_service_unlooping.aspx

    for example.
    Not all DNOs are that generous, but it may soon be forced upon them by legislation intended to encourage network upgrades for embedded generation.

    Given that there are a few triple loops out there it can't really come soon enough, and its a shame there is not more upgrading to 3 phase to the home, as it would make the detection of a lost PEN  a lot easier as well as help the network  volt drop issues.

    Mike.

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