No main earth in domestic supply

[P&Q]

Hi everyone,

I got called in by a customer to install a new circuit for their cooker in the kitchen. So I went over and looked at the main supply and there was no earth. So I told them to get in touch with their supplier and ask about this missing main incoming earth cable and what is the Earthing system, and this afternoon he got back to me, and Scottish Power had simply said, some houses have earth and some really old ones don't - all they have is a Phase and a Neutral cable, and that's it and they're not gonna do anything about it.

I was just wondering, what the deal is with is, should I get back to them myself, or even set up a TT system myself?

Appreciate any advice in advanced guys

 

[Engineer54]

Yes you did hear me right.

If after testing to confirm that the lead sheath is indeed a TN-S earth, what would you see as the problem with extending that earth to the MET?? Your disturbing nothing!!! Quite a different story if you intended to TNC-S a supply neutral, as someone else suggested, that is a complete No No.... But extending an earth that is sitting there, that the DNO would happily connect to the MET for 300 quid, ...You bet i would!!!

 

[malcolmsanford]

Well most DNO that I know will not take to kindly of you clamping their lead sheath cable and creating your own TN-S system. When you get a TN-S or a TNC-S earthing system supplied by the DNO they have a responsibility of maintaining that eath. So this week you confirm that the cable will indeed supply you with a TN-S but in a months time the DNO do work on there system and the TN-S is lost, you will leave that installation without earth.

Normally they would have records of where they have their earths and if they hadn't converted a TT to a TN-S then they would not safeguard that earth on the sheath. If they hadn't supplied that then they will not ensure it is maintained.

As it is their cable your being a naughty boy touching it. I know that some members of our industry pull the DNO fuse and that this is somewhat overlooked, I can't see them over looking the fact that someone as created an earth off their system.

 

[Engineer54]

The DNO will have records relating to area earthing systems NOT individual house installations. Your not creating your own TN-S system, your extending what is already there, and which they are quite happy to charge you 300 quid for!!! This property didn't have any earthing system, just bonding arrangements!!! What's the betting that the original installation got left out, in being provided with a clamped earth on the cable....

As this OP has already installed a TT system for this property, there is no reason why he can't leave this installation in place on the MET, along with extending the supply cables TN-S earth....

If the DNO came into the local area to PME the existing TN-S supply, they would have to change the connection at the cut-out position to suit the new supply in every house/property affected, therefore there not going to end up without an earth at any later date... If the records showed this as a TT area, they would almost certainly convert the TT arrangements to PME, that was one of the basic original ideas of supplying PME systems, to provide a safe functional earthing system to such installations...

Anyway, ....as stated, you are simply extending an earth path that is already there, your not breaking into, or altering anything on the DNOs side of things. Obviously it has to be determined if indeed the existing earth path is TN-S by testing the Ze...

 

[mattmoo1974]

Whack it on TT and your doing nothing wrong.
Start to make your own earthing arrangements without them knowing is going to get you in trouble!
Its earthed at the mo via the water supply your just bringing it up to standards.

 

[malcolmsanford]

And if the TN-S you have created is lost due to repair of a cable by the DNO or replacement of cable for upgrading on just the street side, what would you advise the customer to do then.

Also unless you have a slip-ring arrangement for picking up that earth off the sheath, I personally would not fancy fitting a compression clamp to what might be a 40 year od lead sheath cable.

Sorry I'm a great believer in horses for courses, I'll leave the supply of TNC-S or TN-S supplies to the DNO, if the customer dosen't want to pay a fee to them for doing it, then I'll fit a TT system and charge them my fee.

 

[Engineer54]

Too many ''IFs'' there, ...that frankly aren't going to happen. If a cable is being repaired in a street, then won't that affect every property on that street fed by that supply?? Don't you think, if there was going to be a loss of earthing arrangements, the DNO would be taking suitable remedial actions to those properties???

Extending an earth path isn't in it's self, doing anything detrimental to any system, least of all to the DNO .....apart from losing 300quid maybe. Perhaps if there charges reflected the cost of doing such work, more people would take advantage of having works done by the DNO companies.