Do I need an Earth Rod Fitted?

[JohnW2]

If two phases are involved then as per the diagram one house will be undervolted while the other house will be over volted.

True.
If I wanted to 'argue' (in support of the comment I made), I might point out that the above means that there is a 50% probability that any affected house would experience under-voltage and that, combined with the finite possibility of what you mention below, and the finite possibility that only one phase was involved means that, overall, there would be a greater than 50% probability that any particular affected house would experience under-voltage - but whether that would make that situation qualify as the 'most common' scenario would perhaps be debatable (even though literally correct)

If the isolated section of PEN has no path to Ground then the two houses will be in series across a 400 Volt ( 2 phase ) supply.

Again true. It obviously depends upon the active loads in the two houses, but if they were similar, then that would result in both experiencing under-voltage (both about 200V).

All the above obviously assumes that only two houses are involved. If there are more than two, it gets a bit more complicated.

 

[bernardgreen]

but if they were similar, then that would result in both experiencing under-voltage (both about 200V).

agreed but if ( when ) the loads are not similar the lowest load will be at risk of being overvolted.

A few years ago a cable fault severed one phase and the PEN to a cluster of 7 houses. The supply to one house went up to 300+ volts when the local sewage pump tried to start up. Remedial work ended up with a new 11kV supply being installed for the pumping station to separate it from the houses

 

[JohnW2]

agreed but if ( when ) the loads are not similar the lowest load will be at risk of being overvolted.

Agreed.

A few years ago a cable fault severed one phase and the PEN to a cluster of 7 houses.

That's obviously an even more complicated scenario.

Although I never quite worked out the probable mechanism, a good few years back a fault at the local transformer resulted in one of our phases falling to a low voltage (relative to N) (which is how we became aware of the problem) and another rising to a frighteningly high level (if I recall correctly, significantly over 300V) - but fortunately no harm/damage resulted.

I suppose that experience is a little 'reassuring', in that it indicates that it is at least possible for high over-voltages to not do any 'harm'.

 

[bernardgreen]

for high over-voltages to not do any 'harm'.

Most of the lamps ( incandescent ) blew and ( from memory ) a computor was damaged,

 

[Risteard]

should that not be something like:

After all, TN-S is TN-S (as a simple fact) and that surely remains true even if one cannot see that it is?

No. It would more accurately be stated that it is presented as TN-S at the property, but may not in fact be TN-S.

 

[JohnW2]

No. It would more accurately be stated that it is presented as TN-S at the property, but may not in fact be TN-S.

Nothing I wrote disagrees with that.

I was merely pointing out that if a supply IS TN-S, then it IS TN-S, even if one cannot 'see that it is'. Do you disagree with that?

I think we are all agreed that something which looks like TN-S is not necessarily true/conventional TN-S (i..e. an intact cable sheath all the way from transformer to consumer) - but even that would seem to be of relatively little relevance, since if the sheath of an incoming property is effectively connected to the neutral of the supply 'somewhere', it doesn't make much difference whether that connection is 'at' the transformer or somewhere between the transformer and the user, does it?

 

[Risteard]

I was merely pointing out that if a supply IS TN-S, then it IS TN-S, even if one cannot 'see that it is'. Do you disagree with that?

Of course, but that is impossible to prove unless the DNO assure that it is. (They won't.) It's also becoming exceedingly unlikely to be true.

 

[morqthana]

if the sheath of an incoming property is effectively connected to the neutral of the supply 'somewhere', it doesn't make much difference whether that connection is 'at' the transformer or somewhere between the transformer and the user, does it?

N break here:

vs here?

 

[JohnW2]

Of course, but that is impossible to prove unless the DNO assure that it is.

Indeed - but, as you presumably noticed, I was merely responding to the assertion that TN-S is not TN-S unless one can "see that it is". That would be s bit like saying that a sausage was no longer a sausage if it were locked up in an enclosure into which no-one could see

(They won't.) It's also becoming exceedingly unlikely to be true.

If the DNO cannot, or will not, confirm that a supply is TN-S, then they presumably have no choice but to PME it (if it isn't already PMEd) and describe it as TN-C-S?

 

[JohnW2]

N break here: .... vs here? ....

You've illustrated the situation before the break was repaired.

I was talking about the situation after repair (with a 3C+E cable), when they would have to join the downstream cable sheath (which is providing consumers' earths) to the (repaired) N conductor.

In that situation, the sheath entering consumers' houses (i.e. their installation's earth) would be electrically connected to the supply N - just at some midpoint rather than at the transformer - which, as I wrote, I don't think would really make much difference.

 

[flameport]

I was merely responding to the assertion

No, you are twisting words around, adding others in that you believe should be there all to prove some useless point about the use of language.

While you may exist in a world of legal documents where 10000 words are required to explain even the most simple concept, the rest of the world does not.

 

[morqthana]

You've illustrated the situation before the break was repaired.

No - I was illustrating a break happening after the repair. But in the new section, which would be pretty unlikely - didn't think about that.

 

[ericmark]

@morqthana has shown the problem where a repaired section which made the installation PME has failed a second time. And not so unlikely as one may think, where for example speed humps have caused ground movement no one expected, causing repeated problems in the one area.

We hope there are multiple earths the question is what is the resistance between the two sets of earth rods or other methods of earthing? The resistance and load will determine how much the voltage will swing, and with a housing estate pre-heat pumps, solar panels and EV charging etc, the fault could exist for some time without anyone realising.

But the reduction and increase of load due to use of heat pumps, solar panels, batteries and EV charging means the voltage swings can be far greater.

As to private earth rods, they are not likely to be good enough to have much effect, the problem is the likes of EV chargers and solar inverters are designed to auto switch off if the voltage is out of spec, but they will also auto reconnect, only when someone looks at the number of times this has happened is one likely to be alerted to a possible problem.

I can see what my voltage has been,

but if it was not being talked about here, I likely would not look. We get a report, ⁣but again I have only looked because it is being talked about, how long could a fault exist before we become aware?

I simply don't know, as to if smart meters would report it again I don't know. Until we get lights flicker or bulbs blow, we may not know anything has gone wrong, and with LED lighting will it even flicker, depends on how the bulb is controlled.

However, can't see fitting an earth rod will help that much, I have to fit one in case I get a power cut, and I am using an island supply for essential items like my freezer, but if I didn't have batteries it would simply disconnect, and I would not need an earth rod.

 

[JohnW2]

No, you are twisting words around, adding others in that you believe should be there all to prove some useless point about the use of language.

It's not really anything to do with 'use of language'.

Rather, as you must know, it's that I get a bit concerned when I see apparent assertions which are not strictly or completely correct, particularly when they are written by people whose opinions are (justifiably) usually so highly respected that anything they say or write is probably taken by many to be 'gospel truth' - even if {not really in the present case}, as is not uncommon, they are actually merely personal views with which by no means everyone would agree.

 

[morqthana]

@morqthana has shown the problem where a repaired section which made the installation PME has failed a second time. And not so unlikely as one may think, where for example speed humps have caused ground movement no one expected, causing repeated problems in the one area.

In my road the cables are all under the pavements. They're about 70 years old, so are probably just rotting away in places. And of course the first thing to rot away is the PE conductor...

I was just concerned that if my earth now relies on the neutral conductor in places I might be at risk if that conductor broke.

We hope there are multiple earths View attachment 391687

There used to be lots when we connected metal water pipes and gas pipes etc to the earth of the supply. I've still got a bonding connection on my gas pipe, but IHNI if the underground pipe is now plastic, or not.