Incomplete ring circuits?

[pc1966]

The recent click-bait thread on radial vs ring final circuit descended in to the usual arguments ranging from sane to near-religious, but one issue that was raised among the general noise is the risk of a ring with an open somewhere.

So I wondered if the folk on here that do many EICR and similar work could comment on the following:

• Roughly what percentage of tested RFC do you see with an open ring?
• Is there any more common fault than other (e.g. is E more likely to be open than L, etc)?
• How often are those incomplete rings showing any sign of thermal stress / overheating?

And please folks keep the thread discussion on this one point of open rings, not the general merits of RFC vs Radial, etc.

TL;DR Open ring, any common cause and does it overheat?

 

[Strima]

The amount of discontinuous conductors on a ring will probably be the same as any other circuit, except people notice when half of their radial sockets stop working and do something about it.

 

[Lucien Nunes]

Which means that they usually get rectified, whereas the rings might not until the next EICR. Therefore if the probability of a connection being open is equal for rings and radials, EICRs would tend to reveal a disproportionately high number of faults on rings.

I previously raised the third question and no-one reponded with a confirmed case of thermal damage. I think there is a logical reason why none will be found. Cable CCC is based on a working temperature that will enable the cable to provide a good working lifespan under continuous load. It will withstand short excursions to significantly higher temps and is only likely to sustain visible damage if the insulation softens so much that it deforms at the connections or the conductors or cleats migrate through it. Any cable installed so that Iz is sufficient for a 32A RFC, will probably carry the full 32A by itself (or clear a fault on a B32) without this happening. It will remain in the zone where its working life and its ability to withstand mechanical damage is reduced, but won't actually disintegrate unless otherwise stressed e.g. by crushing. Since most general-purpose and domestic socket-outlet circuits are only ever fully loaded for brief periods, the reduction in durability will not tend to have any real impact and the cables will appear unharmed.

 

[cliffed]

I’ve seen spec 4.00mm,mainly conduit cabling in schools.
If you go up another size you wont get the conductors in.
2.5 mm just the jobby.
Recently did a school block,spec,rings in classrooms,T&E,everywhere else radials 20amp 2.5mm

 

[pc1966]

Also with rings I expect the majority of opens only impact on live conductor, so other other is still current-sharing as a ring and you don't have the full 32A thermal effect on one leg even if most of the loads are there.
[automerge]1598787515[/automerge]

It's not always unprofessionalism, just the need to remedy at reasonable cost.

My apoligies for that wording. On reflection it is not the right thing to say and as you point out sometimes making it safe at an affordable price is by far the best action.

 

[mattg4321]

With regard to switching out a 32a mcb for a 20a, how do you all feel about a live conductor potentially floating around in a back box somewhere if this has been done because there is open circuit rather than multiple sockets from same spur off ring

 

[pc1966]

With regard to switching out a 32a mcb for a 20a, how do you all feel about a live conductor potentially floating around in a back box somewhere if this has been done because there is open circuit rather than multiple sockets from same spur off ring

I think if you have an open ring that is one or two of the 3 conductors it should and can be fixed fairly easily, so I would not accept a MCB change as a fix.

However, if someone has completely opened the ring in to two radials, or has added multiple spurs, you might find that a proper fix is difficult = time consuming = expensive. In this case a MCB change is acceptable in my mind.

 

[GBDamo]

Pubs are a different breed altogether. We would do a 20% test of the installation each year. In most cases I was getting the last 20% so all the rings were left as the years before the lads had just opted for the easier radials. Lots of adapted circuits, countless spurs on spurs. Pubs are awful. Still it’s rare I’ve seen any thermal damage on a ring.

Was doing repairs and maintenance on pubs before lockdown.

They are hands down the worst installations I have ever seen, absolute nightmares ?.

 

[Mike Johnson]

Talking of bad connections, first indication was the smell of fish.

 

[pc1966]

What was that?
Looks a bit corroded as well.

 

[Mike Johnson]

it was a double socket on a very damp wall.

 

[captaincaveman]

I've just counted 4 out of the last 10 EICRs I've done had open rings (mainly Neutrals).
I think 3 of them were in terminal boxes under floors from memory.

Personally I would like to see sockets redesigned to reduce the chance of bad connections. Perhaps using 3 push-in connectors for each of live, neutral and earth? Then even a DIYer shouldn't mess it up or add too many spurs. I'm always coming across bad connections when spurs are involved. Sometimes it's not visually obvious to see whether all the conductors are in place and I suspect a lot become loose when the socket has been pushed back into place (which is why I always pull the accessory out again a little and retighten - especially with 6mm oven and shower switches which are ALWAYS loose!)

 

[cliffed]

I've just counted 4 out of the last 10 EICRs I've done had open rings (mainly Neutrals).
I think 3 of them were in terminal boxes under floors from memory.

Personally I would like to see sockets redesigned to reduce the chance of bad connections. Perhaps using 3 push-in connectors for each of live, neutral and earth? Then even a DIYer shouldn't mess it up or add too many spurs. I'm always coming across bad connections when spurs are involved. Sometimes it's not visually obvious to see whether all the conductors are in place and I suspect a lot become loose when the socket has been pushed back into place (which is why I always pull the accessory out again a little and retighten - especially with 6mm oven and shower switches which are ALWAYS loose!)

Great idea for the push in connection,also love the Colour id on some sockets too,for the cables

 

[Mike Johnson]

Even push fit connectors for socket outlets have failures.