Burnt out leg on Ring!

[walec]

Hi, I have just been to a job who called me because they could smell something and the breaker had tripped. Visual Inspection, I found the Neutral from the Meter on the outgoing side was very loose (where it goes into a 100A DP Breaker before the CU) tightened that and other clamps up. Did some tests on the ring in question, pulled up some boards and found the PVC has completely melted off the cable in places and was melting in others, Customer is not keen on a rewire which I suggested, so I am wondering where I stand if I just replace that leg? and it tests out OK. Thanksl

 

[trebor]

Sounds to me that is probably not a healthy ring ie a break, I would certainly want to know why its melted before replacing

 

[Johno]

You could replace the burnt cable, but you need to fully test the circuit and be 100% satisfied that all is correct, it may of just been down to a bad connection. But it may be down to over load and dodgy wiring, incorrect protection, etc, in which case this will need sorting and the customer needs to understand that you will require paying just to diagnose the fault and this may still result in rewiring the circuit at extra cost

 

[Johno]

Is it RCD and bonding OK, etc.

 

[AIM]

It may be good to undertake Insulation Resistance tests. I would divide ring into sections and test each leg L-N, L-E and N-E anything not getting 100% off the scale should be replaced as rapid deterioration may take place after the melting episode.

Good luck!

 

[walec]

Thanks Guys, when I got there there was no Neutral when I plugged my tester in, not on any circuit which led me to find the loose tail, is that probable cause for failure on the ring if there was a loose connection on the ring as well? I do not know why the tail was loose though, neither does the customer.

 

[nickblake]

they are lucky people , thank good ness the MCB tripped , check check and double check make sure there all is 100% safe they could have lost their house if not thier lives was the cable PVC or VIR , if it was VIR i would insist its rewired ,easier to rewire the house than re buid it or thier lives , if i was doing the work i would insist on a full periodic even to the extent of lifting further boards , making sure all bonding and the CDU was fully up to date ,and also insist on installing smoke detectors to , Fire service offer them free in some area's , you have to cover your self , you need to try and explain how lucky they were , without scaring them , you may have heard about a police woman and her 2 children dying in a house fire ,last month , well i knew the family , so you can see why im so insistant on this

 

[walec]

There is no RCD protection, I think they realised how bad it was when I said to them "I can not believe this did not catch fire, scorched timbers the lot" (I will take a pic tomorrow). I am due to do a full Inspection tomorrow, I am woried about the rest of the house, its very big!. The same supply supplies an Annex with Granny in. I have told them the least it needs is 17th Edition Boards (RCD) (there are 2, 11ways each), bonding is OK. It does bother me though, I still want to rewire the lot so I can sleep!

 

[Johno]

It's a tricky situation mate, but at the end of the day, don't worry about the customers wallet just tell them whats what, that's all you can do. This is the part of being self employed that I hate.


Good luck.

 

[nickblake]

agree with johno part i hate ,going into some one house and basically condeming it and yes you need to sleep at night ,got to be cruel to be kind,
i was thinking about this one , if the installation is a TNCS and there was a neutral to earth fault on the ring and the main neutral of the house is lost as it was then any load would be using the N to E fault of the ring as the return path ,could explain why the cables got melted

 

[walec]

OK, so I spent the day there today, turns out the ring comes from the CU, 20M away, upstairs into bedroom, down stairs into lounge, upstairs into bedroom and a spur off to the stables! There are two 12 way consumer units which are all labeled incorrectly as there has been an Annex built where the garage was and a garage built on the other side, the consumer units bear no logic, there are some suppiles to both dwellings (boards are in the middle) on each board.
Just for good measure the lights in the lounge failed today, I suspect the burnt out ring has burnt through the light cable. I did some IR testing but this place is a nightmare, there is obviously something plugged in or a PIR I could not find that prevented me getting a reading on two circuits (I looked for hours). I should add this is a Barn Conversion done about 20 years ago and then added to 15 years ago. In the end I told them that they should have the whole lot rewired as I could make little sense of it. They agreed but this is a big job for me on my own, especially as it needs to be done sooner rather than later. Take a look at the photos, I have not seen any burnt like these before.

 

[nickblake]

thats very odd could rodent attack be a contributorory factor or cheap cable ,whats the rest fof the cable like , might be an idea to ask your trade body for advise ,i would insist on a full rewire , as you have said its a miricle it didnt cause a fire and looking at it it did catch fire and extinguished its self ,could this be a batch of cable thats faulty or of very poor quality ,ask your trade body send them the pics , think you realy need to cover yourslef with this one ,let us know how you get on

 

[AIM]

Is there a possibility of 400 volts through the installation with a neutral fault on TN CS [expert technical comments welcome]

Regarding lighting IR problems - I have found door bell transformers and TV boosters spurred off in the loft on occasion. The transformers may be giving false readings on top of possible melting issues.

Please keep us posted!

Thanks and good luck

AIM

 

[SirKit Breaker]

It maybe worthwhile asking your customer to check their buildings insurers, they may be able to claim some or all the cost of the rewire. I had a similar event a few years ago when the CU burnt out and damaged all the cables within. The Insurance paid out about £1500 of the claim and put them in a Hotel for a week as well while the work was carried out.

Cheers....Howard

 

[walec]

As a few asked to be kept informed this is still on going. I sent the photos over to ELECSA who requested them when I phoned up to discuss it with them, they have not come back to me though. The customer has spoken to their Insurance but because it did not catch fire they were not interested. So I have locked off the offending circuits and wait on the customer.