Conversion of TT Supply to TN-C-S or TN-S

Sep 30, 2010 3 Replies
D

Here's a pic of a friend's consumer unit:



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you can see there is an underground cable coming in to the house. From my limited knowledge of such things, I would say it's a paper-lead cable.



There is no Earth connection to the cable. The green wire (at the top of the pic) is an earth wire going from the earth bar in the Consumer Unit to a rod outside.



This makes the installation TT, probably because other houses in the street have overhead connections.



Now, there was a thread a while back where I'm reasonably sure somebody was talking about getting a TT supply converted to TN-C-S (PME).



What do you think the chances are of getting the DNO to convert this TT arrangement to TN-C-S and, at the end of the day, is there any real advantage?



Or did I misunderstand and somebody was saying that the DNO was pro-actively converting TT supplies to PME and if only happens to you if they're doing down your street.



Cheers, DaveyOz


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A

paper-lead

somebody

When EDF put 3 phase into my barn, as it was overhead I had assumed it would be TT, however they insisted on it being PME (I had to re-arrange my earthing) as the feed transformer is very close.

AWEM

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B

Whether it can be converted to PME depends on the local network. It is impossible to tell from the photo. Overhead wires do not stop it being PME capable - our network is PME here but most houses are supplied overhead. You can ask your DNO. but they are unlikely to convert it to PME for free nowadays unless they they have to replace the service head for another reason. It is not smelling/smoking is it?! Is PME an advantage? Debatable, but the consensus is yes. You get the additional protection of mcbs operating for (some) faults to earth, but incur the small risk of a lost neutral. That risk is greater with overhead wires as the final connection to your property. If you already have a perfectly good TT system, then I suggest you test the rcds regularly but leave well alone. Regards Bruce

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D

Thanks for that Bruce. I found this document this morning:

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) which gave me the info I needed. Leave well alone is indeed the plan. There's already RCD provision.

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