PME or TT ?

[sprigsteen]

Hi Everyone, New to the site, newly qualified Part P installer. I have encountered two properties which appear to be TT systems with ZE readings of 65 and 100 ohms, on live testing ring main ZS results 0.5ohms and 0.56 ohms. There is no PME earthing connections at DNO cutout fuse. Does this mean the DNO have connected neutral and earth at the pole? How do I know if it is PME? Cheers guys.

 

[JD6400]

I can see the logic behind reusing them , but in my experience getting them to reengage is usually at best problematic .
As I have already mentioned though , the vast majority of the ones I see , have lived in normally very aggressive atmospheres for the past 40 years or more , so are probably not a very fair representation of them in general !?

 

[Knobhead]

Tony are they anything like Parachutes

OK it was late, I kept looking at and the brain didn't klick.

Just thought of another good reason to use the old switch, the incoming tails are there and connected.

 

[Marvo]

I guess we'll just agree to differ. I'm not stating that a VOELCB wouldn't function as a D/P isolator but I think the principal unnecessarily opens the door to other bad practice. If I had an old MCB that burned out or known to be faulty could I use it as a blank in a DB. It would probably be more effective than those blanks you just push into the cover. I wouldn't do this either but going by the same principals then why not?

 

[Engineer54]

I guess we'll just agree to differ. I'm not stating that a VOELCB wouldn't function as a D/P isolator but I think the principal unnecessarily opens the door to other bad practice. If I had an old MCB that burned out or known to be faulty could I use it as a blank in a DB. It would probably be more effective than those blanks you just push into the cover. I wouldn't do this either but going by the same principals then why not?

Don't think anyone is saying that they would go out of your way to use one of those old VOELCB units as an installations DP isolator switch. But if it's already there in place, i'd have no problem at all disconnecting any of it's protective cabling and continuing it's use solely as a DP isolator switch.

 

[Amp David]

Surely even after completing whatever a part p installer course is you would know where to be looking fir something like this. So basic it makes me cringe

 

[Richard3009]

Am I missing something here, can't you just look where the main incoming earth originates from either from an earth electrode TT, the sheath (armour) TN-S or linked N.TN-C-S or PME which to my mind is another bloody acronym that should never be introduced to students why add another.

 

[Knobhead]

Am I missing something here, can't you just look where the main incoming earth originates from either from an earth electrode TT, the sheath (armour) TN-S or linked N.TN-C-S or PME which to my mind is another bloody acronym that should never be introduced to students why add another.

I will say I prefer the DNO’s and the American terminology for PME. CNE Continuous Neutral Earth.
Its plain stupid that in the UK we can’t even agree amongst ourselves what it is.

As for TN-C-S who ever came up with that idea should have been drowned at birth.

BTW Richard, I’m retired from heavy industry where TN-S rules.
We did use IT systems for MV, but that’s a whole subject on its own.