Earth rod

[JohnW2]

It's just as a belt and braces approach. What do you think?

It will do no harm. In fact, it was only at the 11th hour of the most recent revision of the Wiring Regulations that a requirement for all installations (including PMEW/TN-C-S ones) to have an earth rod was dropped - so I strongly suspect that it will re-appear before too long!

It's no different (or 'worse') than having an incoming metal (e.g. water or gas) supply pipe connected ('bonded') to the installations 'earth' - and that is definitely already very much 'required' by regs. Such incoming 'earthed' pipes are known as 'extraneous conductive parts', and if there is some other earthing system, an earth rod is simply another extraneous-c-p.

Having said that, the rod is unlikley to achieve much. The only real 'risk' with a PME/TN-C-S system is that there will be a 'lost neutral' in the supply network, leading to the potential of the neutral and 'earth' within the installation to rise to considerably above true earth potential, However,, as eric has pointed out, the impedance of any domestic earth rod is nearly always going to be far too high to make much difference in that situation.

Kind Regards, John

 

[JohnW2]

Sure, but, after you have hammered it into the ground, how will you test the rod to ensure that it will be effective in the event of a PME failure?

As eric and I have both said, it's unlikely that any domestic earth rod will have a low enough impedance to make much difference in the case o a "PME failure".

 

[JohnW2]

I wouldn't bother but then some of my circuits don't have a CPC (earth wire).

Interesting. Is that common in your (current) country?

 

[EFLImpudence]

Interesting. Is that common in your (current) country?

I presume it is.

It is a block of flats 40 years old so I presume they are all the same - unless altered.
Fifth floor so not that bothered.

Only the kitchen has CPCs and the wiring there is still original.

I have replaced the MCBs with RCBOs - just in case.

 

[JohnW2]

I presume it is. .... Only the kitchen has CPCs and the wiring there is still original.

Interesting - and perhaps rather surprising?

I have replaced the MCBs with RCBOs - just in case.

Might you not just have well waited (for all circuits other than kitchen) until the other circuits are given CPCs (if ever) - or have you done it 'just in case' someone finds something earthed to touch at the same time as touching something 'live' ?

 

[EFLImpudence]

Might you not just have well waited (for all circuits other than kitchen) until the other circuits are given CPCs (if ever)

Why?

It's mine and I haven't done it yet.

- or have you done it 'just in case' someone finds something earthed to touch at the same time as touching something 'live' ?

W e l l - yes, that's their purpose.

 

[JohnW2]

Why? ... It's mine and I haven't done it yet.

You went on to answer that question yourself, when you wrote ....

..... or have you done it 'just in case' someone finds something earthed to touch at the same time as touching something 'live' ?

W e l l - yes, that's their purpose.

Fair enough.

When you say that only your kitchen has CPCs, is there anything powered by the kitchen supply that will result in your pipework being 'earthed', or is all the pipework 'floating'. If the latter, what in your flat (outside of the kitchen) actually IS 'earthed'(for someone to touch?

 

[Risteard]

Yes.

Why do you want to?

Why wouldn't you want to?

 

[JohnW2]

Why wouldn't you want to?

Perhaps because 'earthing things' is a two-edged sword?

 

[EFLImpudence]

When you say that only your kitchen has CPCs, is there anything powered by the kitchen supply that will result in your pipework being 'earthed', or is all the pipework 'floating'.

All pipes are plastic.

If the latter, what in your flat (outside of the kitchen) actually IS 'earthed'(for someone to touch?

Nothing.

 

[JohnW2]

All pipes are plastic.

Fair enough. No 'shock hazard' due to earthed pipes (or, I presume radiators, then"

Nothing.

In that case, I'm inclined to agree that CPCs would achieve virtually nothing. Mind you,the same could be said to be true of the RCBOs you installed ('just to be sure'), couldn't it? (I'm inclined to wonder " 'just to be sure' about what?", if there's nothing earthed to touch)

 

[EFLImpudence]

Mind you,the same could be said to be true of the RCBOs you installed ('just to be sure'), couldn't it?

Yes, I suppose so.

I just realised that's what you were thinking.

 

[flameport]

All installations should have their own earth electrode, such things are now recommended in BS7671.
Most other countries have required them for ever.

However shoving in one of the usual thin copper clad steel rods about 1m long will achieve very little, the resistance will be too high to have any meaningful effect.
On the other hand, installing a substantial metallic grid under your driveway would have a very low resistance, possibly so low that failures such as a broken CNE conductor could be entirely concealed by the presence of it.

 

[ericmark]

possibly so low that failures such as a broken CNE conductor could be entirely concealed by the presence of it.

This has been raised a few time lately, I have measured the earth current, but at this point, I don't know what is acceptable.

I started looking at earth current with my son's narrow boat, mainly considering cathodic protection, and it seems the volts rather than current is more important, each metal has a different voltage compared with other metals in an electrolyte, we all did the Daniel cell at school, but that is some time ago around 1965 in my case.

I noted my father's old house, built 1954, the cast iron waste pipes had completely been eaten away. From 1954 to 2004 when I returned to the house to do some electrical work, all signs of earthing had vanished, except for the party line earth fitted by the GPO. I hunted for signs of where an earth had been removed, I know a line earth fault when I was a boy ruptured a 13 amp fuse, so there was an earth, but when I came to install a wet room in 2004 I could find no sign of any earth.

The thread on main fuse cutout talks about how they thought their house was TN-S but now find it is TN-C-S and my house is both, TN-S when the DNO supply fails, but it leaves the question of how often do we actually test?

We should get an EICR every 10 years (5 years with rented) but dad's house went 50 years.

My earth rod the installer said was something like 1.5Ω, although I note the figure was not entered on the paperwork, I can measure down to 0.1Ω with my cheap loop impedance meter, but I never have. On my to-do list.

However, there is no point in fitting an earth rod unless it is tested,

 

[Taylortwocities]

A dedicated earth resistance tester is the best way.
If you only have an electrician’s MFT, you could just carry out an EFLI test.

Of course, you’d need to know what result is acceptable, you may need to extend the rod, or install additional ones to reach the necessary earth impedance.