Ring Final Circuits (OK I don`t think that Flameport likes them!)

[ebee]

Questions

A bog standard ring final circuit with a 30A amp rewireable fuse or 30A or 32A MCB at the fuseway:-

10 twin sockets on the ring.

1 twin socket spurred at the origin

1 twin socket spurred from the wiring on the ring

1 twin socket spurred from a socket on the ring

1 fused connection unit spurred from the ring and connecting 5 twin sockets on one radial leg.

Assuming a bog standard domestic circuit, floor area reasonable and end to end ring length reasonable and all wired in normal 2.5 T & E cable.

1/ Is that OK?
2/ Remove the ring itself and just leave the 1 twin socket on the radial.
3/ as in 2/ above but add 5 more twin sockets each on their own radial.
4/ Connect two more rings to the fuseway
assuming the fuseway accepts all of the conductors and is mechanically and electrically sound for all of the above options.

Which of those options are dangerous/potentially dangerous or unsafe? (and if so then why?)

 

[Adam_151]

Technically you could argue that they are all compliant, just very rubbish

1/ Is that OK?

Yes

2/ Remove the ring itself and just leave the 1 twin socket on the radial.

Yes, but less than ideal, and very limiting, there is no way to extend the cirucit without going back to/working on the board

3/ as in 2/ above but add 5 more twin sockets each on their own radial.

Technically yes, but it would be like WTF is going on here, no way to extend cirucit without going back to fuseboard and trying to jam 7th conductor in the MCB

4/ Connect two more rings to the fuseway
assuming the fuseway accepts all of the conductors and is mechanically and electrically sound for all of the above options.

Technically its safe, in reaility its insane and a complete pain to work with, I'm going to have to take all 6 conductors out, bell them out pair them, and connect one ring at a time to work out which is which. This is where while technically its one cirucit going by the definations, its three circuits identifying as just one , If I'm testing it on a per circuit basis, I'm billing you for three and making comments about the board exceeding capacity and that a replacement board might be recommended

Found there there was a load of council houses wired with two legs out of the ring fuse, which both went to a large joint box in the floor void, from which individual 2.5 cables would go to each socket outlet. You could argue for it it, but not pretty and when these places were refurbished the case was made for rewring it, and I think the justification was that it is a ring from the board, yet doesn't meet the requirements a ring as per a standard cirucit in that it had more spurs than sockets directly on the ring (0). Yes you could argue that while its not a standard cirucit, its a parallel feed, to a load of branches with overload protection at the far end, But I assume anyone who had the ability to make this case, also saw that it was a folly to do so.

 

[ebee]

So, back to the question I asked, not dangerous, not unsafe

 

[ericmark]

We should inspect and test every 10 years (5 with rented) and also when any electrical work is done, if that is done, the ring final which can have up to 106 meters of 2.5 mm² cable in it, is far better than radials to supply large areas, although one can use 4 mm² or 6 mm² with radials and still use a 32 amp overload, the 13 amp socket is not really designed to have 3 x 6 mm² cables in it, so to spur off means some ad-hock joint in the back box. I am not saying using 16 amp sockets and 16 amp overloads is bad, but in the UK we don't use 16 amp sockets in domestic situations except for caravans and boats.

With a 20 amp overload and since with a ring final we must use cable rated at 20 amp I think considering 2.5 mm² as in the main good for 20 amp is reasonable, we can have 32 meters of cable, to comply with same volt drop rules as a ring final, so we need 3 radials to replace one ring, RCBO's were expensive although the price has dropped now, and of course it needs a larger consumer unit to take all the extra RCBO's.

So much depends on home design, if no where near the 106 meter limit so one could use radials without needing three radials to replace one ring, then with a two up/two down house it is possible radials are a better option, however some one signs for design, and that person must actually design, to fit a ring final or radial or spurs because this is the way I have always done it is wrong, one looks at the building and you select a system which suits the building.

It is not a case of the ring final or the radial being better. We also consider cost, radials are clearly more expensive.

One big question is do we trust electricians who follow? We have two classes of people who work on electrics, one the electrician and two an instructed person or electricians mate or apprentice, the electrician can over see the work of the instructed person, but that person should not be doing the inspection and testing, I am thinking about the Emma Shaw court case. There is nothing to stop the home owner doing DIY on the electrics, if he has the knowledge, or if under instruction, i.e. LABC inspector. But to say a ring final should not be used because DIY people may break the ring, is flawed, it is like saying we need a 20 MPH speed limit in all villages because some one doing 45 MPH had an accident and killed some one in the existing 30 MPH speed limit, if the person is not going to obey the 30 MPH clearly neither will they obey the 20 MPH. So lowing the limit will not help. We have the same with people not doing inspection and testing, there is no case for banning use of the ring final because some people don't obey the rules.

 

[bernardgreen]

This was the ring final in a cottage which a friend purchased about 15 years ago
Every socket was a spur from the ring with all junction boxes accessible.

 

[ebee]

"if I`m testing it on a per circuit basis, I'm billing you for three and making comments about the board exceeding capacity and that a replacement board might be recommended"

Well I do hope you not quoting pricing on a per circuit basis cos some clever cloggs might take issue with you on it.

"making comments about the board exceeding capacity" Not sure how you`d justify that statement either

 

[ebee]

Eric, "We should inspect and test every 10 years (5 with rented)" I think it would only be 10 years (max recommendation) from new then 5 years thereafter anyway . The rest of your post I like

 

[ebee]

Nice one Bernard

 

[ebee]

anyway nobody has said unsafe/dangerous yet.
I live in hope

 

[sparkwright]

Questions

A bog standard ring final circuit with a 30A amp rewireable fuse or 30A or 32A MCB at the fuseway:-

10 twin sockets on the ring.

1 twin socket spurred at the origin

1 twin socket spurred from the wiring on the ring

1 twin socket spurred from a socket on the ring

1 fused connection unit spurred from the ring and connecting 5 twin sockets on one radial leg.

Assuming a bog standard domestic circuit, floor area reasonable and end to end ring length reasonable and all wired in normal 2.5 T & E cable.

1/ Is that OK?
2/ Remove the ring itself and just leave the 1 twin socket on the radial.
3/ as in 2/ above but add 5 more twin sockets each on their own radial.
4/ Connect two more rings to the fuseway
assuming the fuseway accepts all of the conductors and is mechanically and electrically sound for all of the above options.

Which of those options are dangerous/potentially dangerous or unsafe? (and if so then why?)

Your arrangement sounds ok and perfectly acceptable.

Assuming it all tests out ok.

 

[sparkwright]

This was the ring final in a cottage which a friend purchased about 15 years ago
Every socket was a spur from the ring with all junction boxes accessible. View attachment 308294

Nice picture.

I have worked in a 60s bungalow where every single socket was spurred from the ring in the loft - but the JBs weren't all next to each other like that!

 

[ericmark]

Eric, "We should inspect and test every 10 years (5 with rented)" I think it would only be 10 years (max recommendation) from new then 5 years thereafter anyway . The rest of your post I like

I was quoting the IET and UK law, it was not my idea.

"if I`m testing it on a per circuit basis, I'm billing you for three and making comments about the board exceeding capacity and that a replacement board might be recommended"

I have seen this with PAT testing, or to give it correct name, the inspection and testing of in service electrical equipment, one item I had to test was a batching plant, it would take 3 guys 2 days to fully test, inspect, and service, I say service as since on a metal frame, vibration could be a problem, so all terminals tested for tightness unless maintenance free.

I have seen it where charged per outlet, be it a cooker connection unit, fused connection unit, socket, or lamp, how people work out their estimate is up to them, but it hardly changes why one would use ring final or radial.

The argument against the ring final is the chance of overload should the ring be broken. This is only likely if inspection and testing is not done, the same problem exists with lack of an earth connection, the problem as I see it is the plug in tester with loop, has the pass mark as 1.7 Ω and really with a ring final the pass mark is 1.38 Ω, however what needs to change is the tester, not move to radials only.

It is so easy with the right equipment, test a selected socket some where mid ring, and then check ring is intact, once you have a selected socket where you know what the reading should be, it takes seconds to test the earth loop impedance (ELI) and Prospective Short Circuit Current (PSCC) many meters auto change line - earth and line - neutral when selecting, so you know if the ring final is intact. What I think is wrong is the selected socket and readings are not on a standard form.

I can see a problem if they did, as likely many installations the radials and rings exceed the volt drop limits. At a 0.35 Ω in coming we should expect the centre socket on a ring final to be 0.94 Ω line - neutral or 244 amps with PSCC. The line - earth we know should be 1.38 Ω but we should be measuring both, with twin and earth we know the ELI is likely higher than the line - neutral loop impedance, unless there is some other earth connection, like bonding copper water pipes, we should be considering this as an inspector.

I remember in my C&G 2391 exam failing the ring circuit as the resistance was too high for the length of circuit, it was within the limits, but the test board had likely less than a meter of cable, so 0.35 Ω at incomer and 0.8 Ω at socket clearly some thing wrong, I found it, loads of resistors in the wiring, seems the guy building the rig wanted to simulate a whole house, but if those sockets had been used, those resistors would have gone on fire, so the ring final failed. (I passed)

And one does get a feel for what the results should be, and if not what you expect even if within limits it should ring alarm bells.

 

[Risteard]

I was quoting the IET and UK law, it was not my idea.

I have seen this with PAT testing, or to give it correct name, the inspection and testing of in service electrical equipment, one item I had to test was a batching plant, it would take 3 guys 2 days to fully test, inspect, and service, I say service as since on a metal frame, vibration could be a problem, so all terminals tested for tightness unless maintenance free.

I have seen it where charged per outlet, be it a cooker connection unit, fused connection unit, socket, or lamp, how people work out their estimate is up to them, but it hardly changes why one would use ring final or radial.

The argument against the ring final is the chance of overload should the ring be broken. This is only likely if inspection and testing is not done, the same problem exists with lack of an earth connection, the problem as I see it is the plug in tester with loop, View attachment 308298 has the pass mark as 1.7 Ω and really with a ring final the pass mark is 1.38 Ω, however what needs to change is the tester, not move to radials only.

It is so easy with the right equipment, test a selected socket some where mid ring, and then check ring is intact, once you have a selected socket where you know what the reading should be, it takes seconds to test the earth loop impedance (ELI) and Prospective Short Circuit Current (PSCC) many meters auto change line - earth and line - neutral when selecting, so you know if the ring final is intact. What I think is wrong is the selected socket and readings are not on a standard form.

I can see a problem if they did, as likely many installations the radials and rings exceed the volt drop limits. At a 0.35 Ω in coming we should expect the centre socket on a ring final to be 0.94 Ω line - neutral or 244 amps with PSCC. The line - earth we know should be 1.38 Ω but we should be measuring both, with twin and earth we know the ELI is likely higher than the line - neutral loop impedance, unless there is some other earth connection, like bonding copper water pipes, we should be considering this as an inspector.

I remember in my C&G 2391 exam failing the ring circuit as the resistance was too high for the length of circuit, it was within the limits, but the test board had likely less than a meter of cable, so 0.35 Ω at incomer and 0.8 Ω at socket clearly some thing wrong, I found it, loads of resistors in the wiring, seems the guy building the rig wanted to simulate a whole house, but if those sockets had been used, those resistors would have gone on fire, so the ring final failed. (I passed)

And one does get a feel for what the results should be, and if not what you expect even if within limits it should ring alarm bells.

IET guidance only covers the initial periodic inspection, and not subsequent ones which it clearly states at the discretion of the Inspector - taking account of the condition and use of the installation, and maintenance regime etc.

 

[ericmark]

Yes agreed, however not longer than 10 years. My point is you can't say a system is rubbish if you break the rules and recommendations for the system.

There seems to be one item where the IET have created a rule because people fail to test, we can use a double socket on an unfused spur, but not two single sockets, as some one may think first one is part of a ring, I can't see if doing the required inspecting and testing how anyone can make that error?

 

[JohnW2]

1/ Is that OK?

As I presume you know, and as others have said, it would all appear to be perfectly compliant with the regs. Assuming that it currently satisfied the houseowner's needs and desires, any changes one made would therefore presumably be done in the name of 'tidying things up', 'making it more decent' or something like that?

2/ Remove the ring itself and just leave the 1 twin socket on the radial.
3/ as in 2/ above but add 5 more twin sockets each on their own radial.
4/ Connect two more rings to the fuseway
assuming the fuseway accepts all of the conductors and is mechanically and electrically sound for all of the above options.

Which of those options are dangerous/potentially dangerous or unsafe? (and if so then why?)

Again, I can't see any of those non-conformant (let alone 'potentially dangerous'), but, assuming that I understand you correctly, (2) and (3) would presumably be inadequate alone, because they would leave the installation pretty short of socket?

(4) sounds bizarre, although I again can't see why it would be non-conformant (let alone 'potentially dangerous'), but I can't see why one would do it - since it makes the whole thing even more messy/'unfamiliar' than it is at the moment, seemingly for no 'gain' (that I can think of).

Kind Regards, John