Conversion to PME

[matt77aej]

hi can anyone help ? im working at an old house that is 3 phase has no earth installed the property was rewired around 15 years ago so its in generally good health except for the worring lack of earth, ive temporarily fitted a clamp to the supply sheathing which has given me good readings on earth loop etc i reccomended that the owner ask the supplier for a pme system to be installed as i felt this is a better option although when she phoned them they told her to get a local electrician to do it ?? ive never heard of this before neither have i ever done one my wholesaler doesnt even sell the parts, any ideas ??

 

[Adam_151]

Firstly, you should have not fitted an oridinary clamp to a lead sheath, the nature of lead is that it'll deform, (either straight away or over time), meaning a loose connection, in the end (straight away or when its tightened at a later date) you'll crush the cable and it'll go bang

Correct way to connect to the sheath is a sweated connection, but only the jointers have to training to be able to do this in a safe manner!, and lead sheath doesn't always mean TNS! (and even if it did, it may have rotted off), though your ELFI reading indicates that its not the case in this instance

You can't DIY a TNC-S connection, you don't know if the network is to PME standards, the lass on the telephone was probably reading from a script, and trying to say that you should install an electrode and make it a TT system, if you ask her to have it put in writing that the service is suitable for TNCS and allowing you to connect onto the CNE conductor I'm sure they would soon change their tune

 

[Click-Sure]

I always knew privatisation was a bad thing... 'A very bad thing...' (Acknowlege BAS)

 

[matt77aej]

thanks for your reply, the clamp is on a large thick collar so there is no way it can be crushed etc etc altough i didnt like doing this, it is only temporary and with the readings on the sockets and lights being well over 14 and there are 30ma rcds installed. There is no chance of a tt system due to the nature of the building and 3 small children living there i decieded this is the best option,

The lady of the house definately asked for a pme conversion to be carried out, so i think another phone call is needed, many thanks

 

[Spark123]

the readings on the sockets and lights being well over 14 and there are 30ma rcds installed.

14 Mohms??

There is no chance of a tt system due to the nature of the building and 3 small children living there i decieded this is the best option,

Why is TT not an viable option?

 

[matt77aej]

i cant fit a tt system without it being either on the neighbours land, above a celler or digging up a council owned footpath which is why i decieded on a pme, If needs be i will find a way of installing one but would obviously preffer the board to do their thing so i can leave the old type square d board well alone! When i did an earth loop it read 14.92 when im sure that you know it should be a heck of a lot less !

 

[Spark123]

Yeah, on a TN system the Ze should be TN-S 0.8 ohms max or TN-CS 0.35 ohms max.