A cople of earthing questions

[DJM]

1) What does a PME connection look like?
On previous threads it has been suggested (often by JohnD ) to get DNO to fit PME and get rid of the earth clamps. Sounds good, but just interested to see what I will get, and i know you guys like posting pictures

2) How bad is unsheathed twisted (steel?) earth running around the huse?
I have found a couple of circuits with twin in probably rubber coated sheath and the earth is a seperate run in what appears to be unsheathed twisted steel. I realise this is not ideal, but how bad is it assuming it is not touched so rubber coating is not disturbed, and earth returns to CU?

 

[luminaire]

Have a look here at the different types:
//wiki.diynot.com/electrics:earthing_supply_types_and_bonding:earthing_arrangements
Pme is usually associated with TNCS because it will have an earth going directly to the CU.
You mentioned earth clamps when I think you meant eath electrode, which could be replaced. Earth electrodes usually means you have a TT system.
By the sounds of it your wiring is well past its sell-by date, so it's probably a good idea to get it looked at with a view to doing a complete rewire including a new CU and having it upgraded to PME.

 

[Steve]

Dont all earthing systems have an earth going directly into the CU?

Bare twisted wire counds like someone's attempted to add an earth to a circuit which one had none. And rubber wiring should be replaced, especially if its black and crumbly (not saying the grey crumbly stuff is any better though of course!)

 

[DESL]

Bare twisted wire counds like someone's attempted to add an earth to a circuit which one had none.

No - older systems (60's) had twin VIR with seperate multi core steel wire as cpc. Also main earthing conductor of steel wire was used normally connected to outer sheath of incomer via a clamp or sometimes sweated on.

 

[DJM]

thanks for the replies.

The link to the earthing is great, but I was also hoping to see the physical thing to what would be different to mine

I may have used the wrong terminology, buth thought the main earth was connected by a sheath clamp which would g with a PME.

As for the twisted steel earth, I am sure I have seen commented on previously, but can't find it and don't remember whether it was a do immediately job.

Twin in black I am assuming is rubber, but is in pretty good shape and not crumbly

Not easy to see, but in top of picyure you can just see twin black and twisted earth.

 

[RF Lighting]

You currently have a TN-S supply (like this). The earth is connected to the sheath of the supply cable.

A PME (or TN-C-S) looks like this. The earth is connected into the supply head.

(Images pinched from Lectrician)

 

[RF Lighting]

And some real photos from my archive:

TN-S

PME (TN-C-S)

 

[securespark]

Although sometimes you find a pvc cable entering the cut-out & an earth leaving the cut-out and it can be TN-S because the link between N & E bars is missing.

You cannot say with certainty that just because the earth is connected to the cut-out that the supply is PME.

You can also find underground TT supplies too, but that's another story...

 

[RF Lighting]

A few tests soon confirms either way, but generally it is one or t'other. Oh and the PME sticker!

This piccy shows the PME a bit clearer.

 

[Steve]

All that space and they stick the meter an inch from the cutout. Nice pic. Not seen an open cutout before. Is there no restraint on those concentrics?

 

[RF Lighting]

No restraints on the cables, but they run straight into the cavity so the chance of them getting yoinked from the head is pretty slim.

Who else can get away with cables in a cavity?

 

[Lectrician]

I will post my TN-S supply later - I have SPLIT CON feeding my head.

Havn't seen the inside of a cutout! Where you been

 

[securespark]

PME sticker not g'teed!

I have seen many PME supplies without a sticker & 100's of TT supplies (in Staffs) with PME stickers all over them...some joke!

 

[DJM]

Thanks for the pics, very helpful

Any comments on the twisted earth?

 

[IJWS15]

The twisted earth will be tinned copper, not steel.

Took some out when I re-wired our house in the early 90s, built 1950ish and only the socked cirrcuits were earthed, live and neutral were twin rubber insulated, lights were single conductor, earths were single copper conductors twisted togehther at joints.

If it is rubber insulated it goes hard where it has been hot (e.g. where there has been a slightly looses connection) and as soon as you touch it the insulation falls off the conductors.