VERY unusual connection to earth, possible PME system?

[AdamKerr88]

Evening All

I've come across a very unusual situation; I've recently been asked to do a consumer unit replacement on a job but on inital inspection i've discovered that the systems only connection to earth is via a 16mm2 cable between the MET and the netural connection within the henley block. At first i assumed this must be a PME system, however i've only ever seen this done by the DNO within the cutout and never a direct connection to the netural, also there in no sign warning of a PME system.

Has anybody come across this before or is this a serious defect as i suspect...........maybe a home made PME earthig terminal on a TT system :S


Any ideas?


Adam

 

[telectrix]

sounds a bit dodgy. i'd get DNO involved with this one. or make it TT.

 

[Mark.W]

What reading did you get for your Ze?

 

[AdamKerr88]

0.23 ohms ........ So pretty good, could be a PME. Already spoke to the DNO - They're calling me back tomorrow.

I'll see what they say then, apprantly they no longer have access to records of what supply system is in the property.

The meter installed is very new, so surely the connection to earth would have be verfied when this was done?


Adam

 

[Darkwood]

If its a pretty new cutout it should be clearly marked that its part of a PME system otherwise as others have stated it sounds iffy, as you know the connection should be made to the neutral block in the service cutout only if it was a a TNCS system (combined to DNO and seperate on all consumer side)

 

[telectrix]

The meter installed is very new, so surely the connection to earth would have be verfied when this was done?not necessarily. the supplier is not always the same as DNO. meter fitters fit meters. anything else..." not my job, mate"

 

[AdamKerr88]

I've spoke to the DNO, they're sending out someone to do a PME avaliblity test, I tried to explain that I just wanted to know if this was common praticise to connect to PME outside of the cutout however I'm not sure they knew what I was asking. Would I be right in thinking that TT systems generally come in overhead and not from the ground? Therefore meaning this can't be a TT with a disconnected earth rod?

 

[generalbosh]

I've come across a similar situation on a remote village water supply pumping station. The supply looked to be 3 phase + N PME but like your site the only supposed connection to earth was made in the Neutral Henly Block the consumers side of the meter & cutouts.

I gained a similar ZE reading & eventually found an old mangled PME plate on the floor so I'm guessing this was a poor version of PME (although the ZE was more than acceptable. I did convert the earthing system to TT in the end after contacting the DNO - they were less than helpfull so I decided in this particular instance it was the right thing to do.

My thoughts are that because of the age of the installation this was an early example of a PME system ...

 

[Darkwood]

I've spoke to the DNO, they're sending out someone to do a PME avaliblity test, I tried to explain that I just wanted to know if this was common praticise to connect to PME outside of the cutout however I'm not sure they knew what I was asking. Would I be right in thinking that TT systems generally come in overhead and not from the ground? Therefore meaning this can't be a TT with a disconnected earth rod?

TT systems can come various ways and yes usually overhead but can loop from building to building internally so as to be mis-leading, ive had TT enter a house in old metal conduit underground but due to excessive corrosion it had been deemed a TT by DNO which was fine until fault next door used the earth rod i'd fitted as its route but running through the radiators first, clark of works took some convincing that it was external fault until i pulled DNO fuse (safety reasons) and they were still live. Never seen Yorkshire leccy board turn up so fast. It was a corroded street earth system that put this house in such danger and from all accounts ive been told its not too uncommon but when it happens it usually kept under wraps... Yeah just in case someone is killed!!!

Felt good to prove Clark of Electrical Jerks wrong and supprised the DNO that i knew the cause, but helps when your old man used to work for them