TN-S installation not earthed!

[plugwash]

However, is the danger not from the low PFC?

that is an issue but one that can be mitigated, the big problem with using service pipes for the main earth is the risk of them being replaced with plastic.

At 14 ohms Zs on his ring, the PFC is 16A

The PE PFC is yes, the PN PSCC is much higher.

which means (correct me if I'm wrong) that in the event of an earth fault (exposed metalic part becoming live or human in direct contact), the maximum fault current would be 16A

direct human contact won't achive anything like that current anyway.

exposed metalic part becoming live you are correct about.

which would not trip his 32A protection device for that circuit

indeed

causing potential fire or electrocution. So how does that work for a TT installation with even higher resistance?

that is what the main RCD is for, it will trip out on the small earth fault currents typically seen in a TT install.

 

[baldelectrician]

From the picture the REC have supplied an earth- therefore they have a duty to maintain it (at their cost).

If there is no earth it's the customer's problem.

If there is an earth supplied by the REC then it's their problem - end of story.

 

[plugwash]

they could try to argue it wasn't them who put the clamp there though.

 

[baldelectrician]

had the same issue with Scottish Power- went in to the houses either side (private - never local authority) and found exactly the same clamps.

If you get on with your neighbours then have a look.

 

[securespark]

But strictly speaking, an RCD which you should have on a TT anyway will disconnect safely right up to 1666 Ohm.

that depends on the RCD,

Yes, I should have said that figure applies to a 30mA unit. Sorry.

 

[homespark]

Yes, the PSSC is fine as there's no problem with the P & N.

I guess the direct contact voltage would be down to an individual's resistance to earth? Only 16A can flow along the CPC, but if they were in a reduced resistance situation, then it could easilty be fatal.

I understand that an RCD on the main switch set to 100mA would be desireable, as used in TT systems - I checked and there isn't one. The DNO have said they're going to sort it, but who pays is uncertain. I agree that it should not be my friend as whoever messed it up in the first place should fix it, but it may be hard to prove who did what when.

Anyway, I appreciate the replies. It's all very educational

 

[JohnD]

We love pictures

 

[securespark]

Have you been at the ale again, John?

 

[JohnD]

...pictures of interesting or old electrical installations, especially if badly done

 

[Lectrician]

I guess the direct contact voltage would be down to an individual's resistance to earth? Only 16A can flow along the CPC, but if they were in a reduced resistance situation, then it could easilty be fatal.

I understand that an RCD on the main switch set to 100mA would be desireable, as used in TT systems - I checked and there isn't one. The DNO have said they're going to sort it, but who pays is uncertain. I agree that it should not be my friend as whoever messed it up in the first place should fix it, but it may be hard to prove who did what when.

The safe touch voltage is considered to be 50v - To comply to the regs, exposed conductive parts/extraneous conductive parts must be allowed to rise to more than 50v during a fault (25v in agricultural installs).

It is therfore this 50v and the operating current of the RCD which is used to find the max Ze via the rod.....but in any case, it is considered to be 200ohm, although anything above 100ohm should be looked into as unsatisfactory.

 

[JohnD]

... parts must be allowed to rise to more than 50v ...

?is there a "not" missing?

 

[DESL]

I have a lot of supplies like thi one most will have a Ze well within regs but if not phone the emergency number for DNO and report it as dangerous.

This usually gets action from EDF the main DNO in my area and normally get put through to an engineer instead of some dippy office girl.

I will say on several cut out upgrades I've requested they've just changed service fuse and not upgraded to PME

 

[homespark]

It is therfore this 50v and the operating current of the RCD which is used to find the max Ze via the rod.....

But if there ain't no RCD fitted, then the current flow will be the PFC, which in this case is 16A. The MCB won't trip on the ring main and you'll be left hanging onto the live part indefinitely... well at least until someone disconnects your limp body from the mains!

Sorry, John D, no pics as my camera's bust Not much to see, really, just an ugly old cable with a poor excuse for an earth.

 

[Lectrician]

Yes thats correct, but I was answering the theoretical question.

 

[homespark]

Yes thats correct, but I was answering the theoretical question.

No bother. I really appreciate your input