A real moan tonight...

[EFLImpudence]

Ring final circuits have been conventional for well over half a century.

By ring circuit, I presume you are thinking of the 433.1.204 special British invention with and dispensation for undersized conductors.

Whilst any circuit may be extended and wired in a ring formation for volt-drop, Zs or other requirements, it is not allowed to use undersized conductors for that circuit so it is correct to say that lighting circuits are not wired using a ring circuit.


In any case, it seems to have become common for DIYers to think that 'ring' is just another word for 'circuit'.

Therefore they should be corrected - politely and helpfully of course. The alternative is just silly and would never lead to better understanding of electrics and language.

 

[SUNRAY]

Could someone give me a one line summary of the fault.

Loss of supplier N ?
Did the polarity reversal have any Relevance?

Also please consider if someone put one hand on the cu and the other hand on the termination box, I guess they would get a belt across the chest

All I've got from DNO so far is no earths due to metal theft, I believe the N was continuous as I never saw any variation of more than a couple of volts or so.
L/N reversal - I'm not sure if it was like that before I got there but I'd like to say it was [fingers crossed] I haven't been able to complete fault finding due to the earth problem.
Yes a significant risk of shock but only after I removed the sockets from their back boxes which is where the ultimate link between both earths happened.

 

[JohnW2]

Metal thieves at substations tend to go for the Neutral as the risk of fatal shock is much lower than if they went for a phase conductor,,

I suppose so, but that would have to be reasonably knowledgeable in order to avoid a serious risk once they had cut the neutral. I have to say that I have always thought that the amount of exposed cable in a substation seemed to little to justify the risks involved in stealing it - but perhaps that's because I have a little more sense than those who do!

Kind Regards, John

 

[SUNRAY]

By ring circuit, I presume you are thinking of the 433.1.204 special British invention with and dispensation for undersized conductors.

Whilst any circuit may be extended and wired in a ring formation for volt-drop, Zs or other requirements, it is not allowed to use undersized conductors for that circuit so it is correct to say that lighting circuits are not wired using a ring circuit.


In any case, it seems to have become common for DIYers to think that 'ring' is just another word for 'circuit'.

Therefore they should be corrected - politely and helpfully of course. The alternative is just silly and would never lead to better understanding of electrics and language.

I don't disagree with any of this.
I do find that commercial lighting circuits are quite often designed as a ring to reduce volt drop, the alternative is of course to use thicker wiring but a 1.5mm² ring is a lot easier than trying to terminate 2.5mm² or even 4mm² wires into light switches and other fittings. Been there and have the vigh viz T-shirts.

 

[SUNRAY]

I suppose so, but that would have to be reasonably knowledgeable in order to avoid a serious risk once they had cut the neutral. I have to say that I have always thought that the amount of exposed cable in a substation seemed to little to justify the risks involved in stealing it - but perhaps that's because I have a little more sense than those who do!

Kind Regards, John

you should see the tools and methods that have been devised to reduce the risk.

 

[JohnW2]

By ring circuit, I presume you are thinking of the 433.1.204 special British invention with and dispensation for undersized conductors.

You might presume that, and you may be right that Winston was thinking of that, but I think that you can be pretty sure that very few of those who get criticised for talking about 'lighting rings' know anything about any "dispensation for undersized conductors", in any context - so that certainly won't be what most of them are thinking of.

Whilst any circuit may be extended and wired in a ring formation for volt-drop, Zs or other requirements, it is not allowed to use undersized conductors for that circuit so it is correct to say that lighting circuits are not wired using a ring circuit.

Given your keenness on the actual meaning of words, I'm a little surprised to see you saying that it is not correct to say that a circuit wired as a ring is a ring circuit. What would not be correct would be to say that lighting circuits are wired as rings "which have a dispensation for undersized conductors" - but, as above, very few people who talk about lighting rings would even have a clue as to what that meant, so it's certainly not what they would say.

In any case, it seems to have become common for DIYers to think that 'ring' is just another word for 'circuit'.

That is undoubtedly true and, as you say, it makes sense to point that out to them, politely - not least to make sure that they don't waste money and copper on installing an unnecessary bit of cable!

Kind Regards, John

 

[JohnW2]

you should see the tools and methods that have been devised to reduce the risk.

OK - so that would qualify as the 'reasonably knowledgeable I spoke of'. However, I remain surprised that there is enough to be stolen from a substation to justify any significant risk.

Kind Regards, John

 

[bernardgreen]

One good thing about wiring lights as a ring final is that a single fault ( disconnection ) will not disable any light except may one lamp at the point of disconnection.

Of course an un-detected fault exists.

 

[EFLImpudence]

Given your keenness on the actual meaning of words, I'm a little surprised to see you saying that it is not correct to say that a circuit wired as a ring is a ring circuit.

I agree but when we talk about ring circuits we do mean the British ring final circuit.

Also interesting is electricians using RFC as an abbreviation for the ring final circuit. I am sure they would not use it for a lighting circuit that happened to be wired in a ring.

Plus it does not seem to occur to them that it also stands for radial final circuit.

 

[JohnW2]

All I've got from DNO so far is no earths due to metal theft, I believe the N was continuous ...

I don't really see how loss of some (or even all) of the earths, with an intact neutral, could result in what you experienced - you'd then just have a floating supply.

... as I never saw any variation of more than a couple of volts or so.

Variation in what voltage, and measured under what circumstances? ... particularly given that you wrote:

.... I rigged this to see if the volts between CPC and back box are real .... That voltage was changing as rapidly as a fiddlers elbow.

Kind Regards, John

 

[JohnW2]

I agree but when we talk about ring circuits we do mean the British ring final circuit.

When you and I (but not those who get criticised/corrected) talk about ring circuits, we do - but that's only really because you and I use sloppy and imprecise terminology. For a start, we really should (and often do) say "ring final circuit". However, even that is still 'sloppy and imprecise', since Part 2 of BS7671 defines "Ring final circuit" without reference to any "dispensation for undersized conductors" (i.e. it simply defines such a circuit as a circuit "arranged in the form of a ring"). Hence, if we wanted to be non-sloppy and precise when wanting to refer unambiguously to the "British ring final circuit", we would really have to talk of "a ring final circuit which complies with 433.1.204 of BS7671"!

Also interesting is electricians using RFC as an abbreviation for the ring final circuit. ...

... which, as you go on to imply, is sloppiness in the extreme, since the only alternative that one wants (should want to!) make a distinction from is usually a Radial Final Circuit!

I am sure they would not use it for a lighting circuit that happened to be wired in a ring.

I'm also sure that they wouldn't - but, ironically, as above, they would (in terms of the 'correct' {formal} definition, which is what usually matters to you) actually be correct in calling it a Ring Final Circuit!

Kind Regards, John

 

[JohnW2]

One good thing about wiring lights as a ring final is that a single fault ( disconnection ) will not disable any light except may one lamp at the point of disconnection.

The same could be said of a ring final circuit for sockets - but, in either case, whether or not it is "a good thing" is somewhat debatable because, as you go on to say ...

Of course an un-detected fault exists.

Kind Regards, John

 

[SUNRAY]

I don't really see how loss of some (or even all) of the earths, with an intact neutral, could result in what you experienced - you'd then just have a floating supply.
Variation in what voltage, and measured under what circumstances? ... particularly given that you wrote:


Kind Regards, John

THE L - N voltage was constant, the CPC [DNO] to TT was all over the place, varied between 50-200V roughly.
The lamp bulb would not have been out of place at a mobile disco.

 

[bernardgreen]

"a good thing" is somewhat debatable

That fault on a ring of sockets does not leave parts of the house in darkness until the fault is found.

 

[Adam_151]

Reminds me of a fault I went to a while ago, TN-CS supply to a farm cottage type property (no outbuildings, not farmhouse, just a worker's cottage), reported issue was no hot water and getting shocks off pipework, the no hot water was quickly ruled out as conincidental, the thermostat on the immersion was faulty, seemed the contacts had been high resistance overheated a bit and managed to become either open or very high resistance (I cant remember), but anyway it had no bearing on anything else.

Zdb was approx 0.20ohms, switched off, disconnected main earth and did the test to incomming earth... still much the same. Went to put earth back in the CU and it arced a bit, thats not right, left it out for a moment, put a temporary earth electrode in the front garden (long drill bit), wander lead back into the house, tested between lead and earth bar in CU, nothing, tested between lead in DNO earth and got about 193v (fluctating slightly). I must admit I never thought about putting a lamp across it. Put a call into the DNO while drove back to town to get a new immersion stat from the wholesaler. Got back and found the DNO chap was already on site* and had verified the fault existed and was scratching his head and making phone calls

*I got a call back from what seemed to be a supervisor, who must have seen the ticket and wanted to confirm that I was reporting a PME earth to ground voltage of 193v, not a phase, neutral voltage of 193v and seemed to prioritise the call following this.

Sunray, does it look like this installation is off a smallish transformer which supplies only a very few customers?