how to identify a pme system help

[lucus]

hi all
i am just wondering how can i identify if a properly that used to be TT has been upgraded to TNCS (pme) one i recently done a job in used to be feed from a pole but now has been upgraded to underground concentric cable would you say this is pme?

 

[pushrod]

Don't mean to be pedantic (do you believe me?) but a "Ze test across L and N" wouldn't be a Ze test.

Apologies - With a TN-C-S the earth is bonded to the PEN, if you tested across the live and earth at the CU (having disconnected the bonding) and then did the same test across the L and N wouldn't you get identical readings proving it was a TN-C-S.
With a TN-S (because the earth conductor is separate all the way back to the transformer) then you would get different values with the Ze compared to the L and N test. Yes ???

So that would allow anyone to recognise a TN-C-S / PME?

 

[Deleted member 9648]

No you cant,only way to be sure is to contact the DNO.
Looking at the poles in the road will give you an idea ,if PME is available every second or third pole will have an earth wire down it.

 

[pushrod]

not really possible if there is no earth

am i missing something here?

Apologies was asking a related question of my own rather than answering the OP.

Lucus: even if it is PME i believe it is the DNO who have to bond the earth to the PEN as it is their responsibility.

 

[Davey101]

Agree with Wirepuller on this one.
Good luck getting any sense whatsoever out of the supplier.
Write them a letter, you will never get back the half hour of your life you waste on the phone to them.
Agree about the poles, they should have a yellow pme label on them.

 

[ezzzekiel]

there is no way of telling, you could open the service head and see if its converted (link accross n-e) but even that isnt a guarantee. they either converted to pme and screwed up by not fitting the earth or its still tt

 

[Spudnik]

Chaps,

I understand the OP to be asking IF pme may be available.

The way i normally check is to test between L & N on the CU as i described in a previous post.

This is the ONLY way you can check and is basically what the DNO do, but they do the check at the cutout.

If a reading is obtained then it should be present, and the DNO can then be contacted to book a "PME enquiry"

 

[aptsys]

What does that tell you other than the prospective short circuit current? Agreed that if the supply is suitable for PME then this would be equivalent to Ze, but only the DNO will know if the network is suitable for PME and that is something you can't test.

 

[Des 56]

The only sure fire way is ask the supplier
They are the only people who know if the neutral has been spiked along its route

There is no test
You can check other properties nearby to give an indication or as suggested,look at the posts for the earth + spike

 

[jonthespark]

I think the thread of this has been lost. If electricity supplier has provided an earth wire it is either TNCS (PME) or TNS. If no earth wire from cut out or clamped to cable sheath then it is TT and an earth rod is needed.

 

[Deleted member 9648]

I think the thread of this has been lost. If electricity supplier has provided an earth wire it is either TNCS (PME) or TNS. If no earth wire from cut out or clamped to cable sheath then it is TT and an earth rod is needed.

Not entirely true, even if no earth wire provided TNCS may be available on request to the DNO.
In nearly all circumstances I'd much rather TNCS than TT,a rod is always going to be an unreliable earth due to ground conditions,and possible interference/damage being in an external situation.

 

[aptsys]

I'd rather have TN-S, TT then TN-C-S.

 

[pushrod]

I'd rather have TN-S, TT then TN-C-S.

What is wrong with TN-C-S ?

 

[Spudnik]

There are many opinions on PME.

Some argue that should the neutral be lost on the network, then effectively, you have no earth.

However, this is not really true, as the pme is spiked multiple times underground from the substation.

 

[Davey101]

There are many opinions on PME.

Some argue that should the neutral be lost on the network, then effectively, you have no earth.

However, this is not really true, as the pme is spiked multiple times underground from the substation.

Which is why you must enquire to make sure it has been 'spiked' i.e is actually pme.