2 circuits done. 2 to go.

[JohnW2]

That's not quite clear cut, parallel feeding is permitted, as is downstream protection. Ironically parallel feeding with 2x2.5mm² could potentially be with a 50A OCPD

That only really applies (or, at least, is only straightforward) if there is only one load (or potential load) on the circuit.

If there is more than one load/outlet, the 'second' cable has to go back through (and be connected to) every one of them - one can't just take a cable from 'the last one' back to the origin to create a ring.

Kind Regards, John

 

[SUNRAY]

That only really applies (or, at least, is only straightforward) if there is only one load (or potential load) on the circuit.

If there is more than one load/outlet, the 'second' cable has to go back through (and be connected to) every one of them - one can't just take a cable from 'the last one' back to the origin to create a ring.

Kind Regards, John

Indeed but it does allow a cable to be used on a larger OCPB than the ccc of each cable.

 

[ebee]

Well if you had only one point at the half way stage per cable length it would be a para path therefore having the merits of a 5.0 live conductor or 4 , another ring I suppose.

Anyway Ring Finals comply and have their uses and have pretty much passed the test of time really. But out of favour with a few (or many) understandably so.

The point was though it`s a Ring (Final) Circuit in the installation but you could have a Ring Main in the street or in the transmission distribution area and the Main and the final are different and should be differentiated. Like I also said "Spur" is often wrongly used too.

Actually so is "Live" , Line and Neutral are both Live (Not, by convention, a PEN or CNE Neutral though). A Live conductor normally carries current as part of its intended function or really the function of the cable etc . a cpc (Earth) carries current of an earth fault.

I will not mention RCDs (Oh Paradox - I just did!)

 

[RandomGrinch]

Sorry, I'm not going to add anything useful to this thread, but some recent observations came to mind - feel free to ignore!

If we want all supplied by same fuse, since often there is a fuse in the boiler, then the supply would need to come from the boiler, connecting to same FCU would not help, idea is it is claimed turn off boiler and all is isolated.

This was something that popped into my YouTube feed the other day - an overdramatic portrayal, but an interesting problem (Eureka moment from 10:30)...

And to cement the point, here is a pic of an abomination found in the plumbing forum!

The top cable is L, N and S/L from the boiler. The only marking was some felt tip on the green/yellow at the boiler.
The right cable goes to a thermostat that was about to be replaced - green/yellow cut off here, but exposed at the thermostat and S/L becomes blue - no sleeving or markings anywhere.
Both this junction box and a second thermostat (connected to the bottom cable) were unknown to the original poster. It was very confusing for them!

Ring mains have been in service for a century or more. Sadly I threw out a load of books etc handed down to me by an elderly friend a few years back, one of which was akin to our current OSG which clearly showed how to install a ring main in a house using porcelain or glass insulators

And if anyone is interested in a few photos showing the construction of a house in 1913, I recently came across these:

Putting a House on a Hill - or How to build a house in 1913!

Following on from a recent thread (talking about the benefits of keeping old books), I was remembering books from my childhood. A set of books fondly remembered, but sadly missed, was "The Children's Encyclopedia", by Arthur Mee. .... So, I had a look around eBay, and bought myself the full ten...

www.diynot.com

Unfortunately, there are only a couple of pictures of the electrics :

 

[JohnW2]

Indeed but it does allow a cable to be used on a larger OCPB than the ccc of each cable.

Of course. If one runs both cables, in parallel, to every point in the circuit, then one has effectively just doubled the CSA of the cable (to provide an 'effective CCC' which is adequate, and which is not less than the In of the circuit's OPD).

That's different from the "BS7671 ring final", which allows the CCC of the only cable between points on the circuit to have a lower CCC than the In of the OPD.

Kind Regards, John

 

[SUNRAY]

Of course. If one runs both cables, in parallel, to every point in the circuit, then one has effectively just doubled the CSA of the cable (to provide an 'effective CCC' which is adequate, and which is not less than the In of the circuit's OPD).

That's different from the "BS7671 ring final", which allows the CCC of the only cable between points on the circuit to have a lower CCC than the In of the OPD.

Kind Regards, John

Yes but it is still a legitimate means of using a smaller cable than the size of OCPD.
As is using down stream protection and some on here seem to advocate small cable feeding resistive load on larger OCPD (1mm² oven cable on 32A MCB for example).

 

[JohnW2]

Well if you had only one point at the half way stage per cable length it would be a para path therefore having the merits of a 5.0 live conductor or 4 , another ring I suppose.

Exactly.

Anyway Ring Finals comply and have their uses and have pretty much passed the test of time really.

That's why I'm essentially 'neutral'. Both the pros and cons (relative to radials) are pretty trivial, and roughly balance each other

But out of favour with a few (or many) understandably so.

Indeed - but I don't fully understand why some people's 'anti' views are so strong - as above, I really don't thing there is a strong reason for favouring one approach or the other.

The point was though it`s a Ring (Final) Circuit in the installation but you could have a Ring Main in the street or in the transmission distribution area and the Main and the final are different and should be differentiated.

I agree. That's why I've been saying that, although some of the hypothetical within-installation arrangements he mentioned could have the same electrical characteristics as a distributor's "ring main", I personally think it's better to not use that term within an installation. Having said that, in reality if someone talks about the 'ring main' supplying sockets within their house, we all not 'what they mean'.

Like I also said "Spur" is often wrongly used too. .... Actually so is "Live" , Line and Neutral are both Live (Not, by convention, a PEN or CNE Neutral though). A Live conductor normally carries current as part of its intended function or really the function of the cable etc . a cpc (Earth) carries current of an earth fault.

All true, and I agree that it is reasonable to explain the 'correct terminology' to those who make these mistakes but, again, we all know what they mean when they talk of "spurs" or "live".

The electrical industry itself is not immune. For example, I frequently mention my personal dislike of using the term "continuity testing" to refer to quantitative measurement of small resistances ... and it also rather seems that it was the industry itself who were responsible for the ridiculous "plug top" term to describe a plug There is also an issue when the industry continues to use its own 'correct' terminology in relation to things relevant to the general public when the vast majority of the general public use, and understand, different vterminology - "low voltage" and the lamps/bulbs issue come to mind.

One could go on about such things for ever but, as I always say, what matters is that we have a means of 'clear and unambiguous communication', whatever the considerations of 'right and wrong'

Kind Regards, John

 

[securespark]

The whole point of the specific BS7671-defined ring final circuit, is that it is a 'dispensation' which allows one to 'break the rules' of other regs, by using a cable with a CCC less than the In of the OPD. One could not do it if the circuit were supplying something other than 'accessories to BS1363' and/or if the OPD was something other than 30/32A.

Just looked up some BS EN numbers in MK's catalogue and sockets, connection units and flex outlets are all BS1363, 20A DP switches are EN60669-1 and 32/45A DP switches are BS3676.

So, in the ancient and recurring discussion about how best to feed appliances on a ring final circuit, a 20A DP switch above and a socket below would not strictly comply.

Also, the requirements for the ring final offer the option of mineral cable of 1.5mm² for all conductors.

I remember a colleague retro fitting a new board to a MICC installation. He decided the best way was to mount the new board onto the old MK metalclad one. He didn't want to remove the glands and bend the cable. Then he realised all the ring finals were connected through the old MK metal CU, thus he could not do a traditional end to end reading on the sheaths.

 

[JohnW2]

Yes but it is still a legitimate means of using a smaller cable than the size of OCPD.

...but that's not really what you are then doing - rather, you are using two cables in parallel (both connected to allpoints in the circuit) to emulate a single cable of larger CSA.

It's not conceptually any different from considering (as we do) the overall CSA (hence CCC) of a number of strands in parallel in a single stranded conductor.

As is using down stream protection and some on here seem to advocate small cable feeding resistive load on larger OCPD (1mm² oven cable on 32A MCB for example).

I have absolutely no problem with downstream overload protection (but not 'fault' protection). 'Overload' (as opposed to faults) necessarily arises in connected equipment and since the current is necessarily the same everywhere in the current path to that load, it doesn't matter a jot as to where in the circuit the OPD is. Indeed, from the point of view of 'cable protection', it doesn't even matter whether the OPD is in the L or N.

Fault protection is a totally different matter, since if it is an L-E fault, the fault current will not exist downstream of the fault (and will not travelin the neutral conductor) so a downstream OPD would not be aware of it.

Kind Regards, John

 

[ericmark]

I seem to remember 88 meters limit for ring final with 2.5 mm² cable, and 4% volt drop, when we went to 5% it went up to 106 meters.

It seems a lot, but by time you take in the 1/3 rule on drilling beams, very easy to exceed. What seems odd is we don't seem record the lenght of cable used, or volt drop.

I at one point did worry about exceeding the volt drop, but no one ever seems to test it, may be just as well, if it was an EICR failure to have too much volt drop, I think many would fail.

 

[JohnW2]

Just looked up some BS EN numbers in MK's catalogue and sockets, connection units and flex outlets are all BS1363, 20A DP switches are EN60669-1 and 32/45A DP switches are BS3676. .... So, in the ancient and recurring discussion about how best to feed appliances on a ring final circuit, a 20A DP switch above and a socket below would not strictly comply.

We've been through this countless times before and, as you say, such switches are ('strictly speaking') seemingly not allowed on bs7671 ring final circuits. Quite apart from that reg, there are also arguments about whether it is acceptable to have a "20A switch" on a 32A circuit.

Also, the requirements for the ring final offer the option of mineral cable of 1.5mm² for all conductors.

They do, and no-one really seems to understand why. Whether T+E or MICC, it is still, of course, required to have a CCC of at least 20A.

Kind Regards, John

 

[JohnW2]

I seem to remember 88 foot limit for ring final with 2.5 mm²

What are you referring to? If that (about 27 metres) were the case, then why would you always talk about the maximum length of a ring final being 106 metres?

In any event, as i recently wrote, what you say about the difference between 'maximum circuit length' for rings and radials is misleading, since the length of a ring is the total over both 'legs'. Hence, if the maximum ring length is 106m, that means that the furthest socket can be no more than 53m from the origin - not dramatically different from the figure for a radial.

Kind Regards, John

 

[JohnW2]

.... And to cement the point, here is a pic of an abomination found in the plumbing forum!

True - but, as you know, that abomination would become BS7671-compliant (but not very 'nice'!) if the G/Y were over-sleeved with brown at both ends

Kind Regards, John

 

[ericmark]

What are you referring to? If that (about 27 metres) were the case, then why would you always talk about the maximum length of a ring final being 106 metres?

In any event, as i recently wrote, what you say about the difference between 'maximum circuit length' for rings and radials is misleading, since the length of a ring is the total over both 'legs'. Hence, if the maximum ring length is 106m, that means that the furthest socket can be no more than 53m from the origin - not dramatically different from the figure for a radial.

Kind Regards, John

I thought I had corrected that before posting?

 

[ericmark]

True - but, as you know, that abomination would become BS7671-compliant (but not very 'nice'!) if the G/Y were over-sleeved with brown at both ends

Kind Regards, John

Not if you take note of the full stop. And the need to have an earth run even if not used.