A broken ring issue......?

[HappyHippyDad]

Evening..

I have completed EICR and discovered an issue with the ring.

The ring serves the whole house. A previous report from 2 years ago had it down as broken and they changed the 32A mcb for a 20A mcb. The client new this and has rightly asked for the fault to be found.

When I tested the ring at the CU r1, r2 and rn were all adequate (r1=0.31, r2=0.72, rn=0.32). However, at the vast majority of sockets r1, r2 and rn were all showing >1999ohms.

I did start writing out my ideas but I've just deleted it as they sounded poor and I have to get the boy to bed!

Something along the line of a very long radial off one of the sockets!!??

Any thoughts welcome.

 

[polo1]

Lollipop?

 

[Octopus]

Am I being dim but I don't understand the comment about >1999 ohms .....

 

[buzzlightyear]

When I tested the ring at the CU r1, r2 and rn were all adequate (r1=0.31, r2=0.72, rn=0.32).

come again !

 

[Dave OCD]

Me too, can you elaborate please HHD ? Do you mean these readigs are obtained while attempting a 'figure of 8' test at the sockets ?

 

[buzzlightyear]

The ring serves the whole house. A previous report from 2 years ago had it down as broken and they changed the 32A mcb for a 20A mcb.

to a radial yes!

 

[buzzlightyear]

the clock ticking on this one.

 

[westward10]

A ring final over the whole property giving an R1 of 0.31 immediately rings alarm bells. Sounds to me like it is a ring final, partially and then a series of radials.

 

[westward10]

Am I being dim but I don't understand the comment about >1999 ohms .....

No continuity, open circuit. Pretty obvious.

 

[HappyHippyDad]

Guys I am sorry. I've been at the beach all day and the cloud and wind has masked the UV and I'm a bit spaced out at the mo. I'll answer the questions properly over the next few days and reread what I wrote in the OP.

 

[buzzlightyear]

I'm a bit spaced out at the mo

what head in the clouds !

 

[Octopus]

No continuity, open circuit. Pretty obvious.

Hum ..... But he's got got good readings, end to end at the cu ..... If I understand the op correctly .... So I am still puzzled....

Wonder what the Zs readings were ?

 

[westward10]

He has continuity at the CU which seems short to cover the whole property but most of the sockets show open continuity indicating a short ring final and multiple radials.

 

[polo1]

Blimey, thought it was only the telly shows that did the long pause before announcing the outcome!

 

[Octopus]

How old is the property?

There is an estate near me, late 1960's at a guess, where the ring holds loads of junction boxes, then most sockets are effectively Spurs. So the basic ring is above the ground floor ceiling which would give a fairly short ring, and the readings HH has seen.

Could this be the answer?

EE boys do this now ......

 

[Flanders]

I guessing there are 2 sets of cables at the sockets so it looks like a ring but is just a load of radials spider wired probley from junction boxes or connector blocks and tape , i imagine if you start lifting floor boards more will be revealed , may be easier to rewire than fault find.

 

[Toneyz]

Evening..

I have completed EICR and discovered an issue with the ring.

The ring serves the whole house. A previous report from 2 years ago had it down as broken and they changed the 32A mcb for a 20A mcb. The client new this and has rightly asked for the fault to be found.

When I tested the ring at the CU r1, r2 and rn were all adequate (r1=0.31, r2=0.72, rn=0.32). However, at the vast majority of sockets r1, r2 and rn were all showing >1999ohms.

I did start writing out my ideas but I've just deleted it as they sounded poor and I have to get the boy to bed!

Something along the line of a very long radial off one of the sockets!!??

Any thoughts welcome.

I would expect a r2 of approx. 0.52 unless it's a cpc of 1.0mm2 however I'm a bit confused regarding the 1999 ohms. Is this an old house with possible j.b's under the floor could be a ring with multiple spurs. I assume that all the sockets work in that case you should get a reading of r1 + rn.

 

[ChrisElectrical88]

I would expect a r2 of approx. 0.52 unless it's a cpc of 1.0mm2 however I'm a bit confused regarding the 1999 ohms. Is this an old house with possible j.b's under the floor could be a ring with multiple spurs. I assume that all the sockets work in that case you should get a reading of r1 + rn.

Readings are pretty much bang on for a 1.0mm ring. The ring is around 40m long which is short for a whole house. As westward said earlier you have spurs coming off

 

[Richard Burns]

I would concur with Murdoch spider ring approach, it seems the most likely, but I thought they were a 50's invention.
Possibly someone added a few sockets to the ring normally at a later date which would account for some of the sockets having an end to end reading.
In potential if it is a spider ring it can be a safe way of doing a ring but it is not normally accepted practice now.

Another possibility is if someone DIYed the ring to add more sockets and took a new cable to another socket to "maintain the ring" and disconnected the actual ring cable that would have made a figure 8 ring thereby leaving a small ring with a long spur on spur on spur....

 

[HappyHippyDad]

Thanks everyone for your thoughts. The client is keen on a rewire of the sockets. I have suggested some fault finding first as it could be far cheaper, but he has decided to stay in the property rather than sell it and says he just wants new wiring to see him through to the end so he doesn't have any hassles.

I'll give an update to whatever I find after I've carried out any work.