Bridged Ring Main

[dunny]

I have been doing some electrical work on my house (extending lighting and socket circuits into my extension). I asked a professional to come and test the installation before I cover up and he has founc a couple of faults.

The first was minor and totally my fault, it didnt show up on the test but on his visual inspection. I had a 20a junction box joining 2 x 2.5mm cables together. I changed that while he was there, retested and all was fine.

The second though was a) slightly more important and b) very unexpected. He found a bridged ringmain and traced the fault to the ringmain extension that powers my conservatory (done by the Installer). He has advised that whilst not overly dangerous it should be changed.

I can still access the area under the floor and I dont want the original installer back. I have some experience doing my extension wiring (which passed fine) should I try fix this myself?

 

[HDRW]

He found a bridged ringmain and traced the fault to the ringmain extension that powers my conservatory (done by the Installer). He has advised that whilst not overly dangerous it should be changed.

I can still access the area under the floor and I dont want the original installer back. I have some experience doing my extension wiring (which passed fine) should I try fix this myself?

Hmmm... It could be that both ends of the new ring were connected into one socket (hey, if a ring is good, two must be better, surely? ) but that's unlikely since it means four wires into each terminal, which is hard to do. If this is the case you just need to remove two of the cables from the socket (one new and one old) and connect them together. How to connect them is a common topic in here!
Or it could be that the two ends of the new ring connect to two different sockets, which are still connected together as before, in which case this "connecting together" cable needs to be removed, but if there are other sockets in that connecting run, it gets more complicated!

Did he point out exactly what the problem was - can you draw a diagram of what the current situation is, and what you're going to do to fix it? This sort of thing can do your head in, so drawing it "explains" it to yourself and others, I've found.

Cheers,

Howard

 

[dunny]

I think its the latter. I can see the new cables that come in under the floor and I can see the 2 JB's that connect them. I can also see that 1 of the cables has been joined into an existing socket but I cant see where the other cable goes, my guess is that its off to another socket but I dont know which one. The one thing I can say is that they at least its on the same circuit.

Is there a simple way of finding which socket it has been connected to?

I have tried drawing it but it left me confused!!! I will have another go once I have identfied which socket the other cable goes to.

 

[breezer]

Is there a simple way of finding which socket it has been connected to?

dissconect it nd see what doesnt work

 

[dunny]

Doh! But if its a ring it will still work wont it?

 

[pdcelec]

Report the installer to LABC since this work should be to Part P.

 

[dunny]

pdcelec - the conservatory was installed about 3- 4 years ago so Ike guess part P didnt apply. The main house was wired professionaly probably about 4 - 5 years ago, the installer of the conservatory did his bit, I did the extension. After taking advice on this forum from the likes of Damocles, Ban-All-Sheds and Brumtrician I decided to get it tested(I wanted mainky to make sure my work was OK). The test revealed the mistake on the extended ring fitted by the conservatory installer. The spak (who is a recent friend of mine) was momentarliy confused by the readings he was getting (he had a device with a 3 pin plug on it that once plugged in gave some reading to him). He was expecting these readings to increase towards the centre of the ring but he could tell from experience that something wasnt quite right - he thinks it is a bridged ringmain

 

[pdcelec]

By bridged do you mean there is a figure of 8?

 

[Lectrician]

You paid for a PIR - pay for a spark to put it right - or atleast tell you what EXACTLY is wrong.

very open ended with what you have said. Photos would be great.

 

[Adam_151]

There is a section towards the end of this that explains how bridged ringmains are tested for, incase you are interested:

http://www.tlc-direct.co.uk/Book/8.4.2.htm

 

[dunny]

Yes I think so. I think the new ring has been attached to 2 different sockets on either side of the room!!

Adam - thanks for that - worth knowing in this case.I have access to a multimeter so I could probably check.

The thing I can get my head around is that if it was bridged wouldnt there have to be 3 connections in the JB's ? There are only 2 and no other unterminated cables anywhere!!

And only 2 in each socket...

 

[pdcelec]

If there are two cables in each socket how can the circuit be bridged?. Does the electrician mean that there are two ring mains and there is a crossed leg at cu?

 

[dunny]

He didnt undo the JB's or pull the fronts of the sockets off but the readings he was getting where not right. He knows his stuff and he had no more time to check further but said he thinks there is something odd going on. I am going to trace the cables to see.

I dont think he means there is a crossed leg at the CU though

More info - House sockets are wired Front and Back (not upstairs and down. Cant see all the cables correctly but I can say that I have 2 cables coming from ring upstairs, 2 going out to conservatory ring, and 2 going off to the rest of the original downstairs ring (just at the rear). There are 2 JBS under the floor and both have only 2 cables each in, no sockets have more than 2 cables in so it cant be bridged right??

 

[pdcelec]

It could be bridged across the two circuits somewhere but turning off one of the circuit breakers would prove this. What is the electrician actually saying is wrong?

 

[dunny]

He is saying that the pattern of readings he has taken (which according to him rise as they get towards the centre of the ring) are not behaving as he would expect. He did say that it is hasnt been crossed between circuits as when he turns off the appropriate breaker the sockets are dead (again tested with his meter). I think the upshot is that he wasnt happy with the readings and had no more time and so couldnt investigate further. He did say that he wasnt overlay worried but would prefer me to lvate the problem. He will come back and retest at a later date.

Is a bridged ringmain, dangerous / out of regs?