Fault Finding

[rolyberkin]

This is not my job and is an issue a colleague at work is having with his house wiring, but as I am doing my fault finding unit shortly will run it by you all out of interest to see whether I am thinking the right things.

A work colleague has come in today with the following problem:

He lives in a 1950's house and few weeks ago his consumer unit started smoking and three of the MCB's had burnt out, this took out the kitchen and dining room, he had the insurance company in due to the damage to the consumer unit and they refused to pay out as they say his board was overloaded. I am waiting for pictures of the old and new board and test results of installation out of interest.

He employed an electrician who replaced said consumer unit with a new high integrity split board but has not rewired the property (Personally I think a rwwire this should have been considered given the age of the cable and the previous fault, he states this wasn't given to him as an option by the Sparks). There doesn't appear to be a fault given for the burnt out MCB's over and above perceived continual overload.

The sparks apparently finished last night and provided a test sheet, my mate plugged in his hoover downstairs and the MCB and RCD tripped immediately. Power has been lost downstairs and partially upstairs. He has re engaged the MCB and RCD which has stayed in but he still has no power to some sockets downstairs and some upstairs, he has called the electrician back but wanted to know my views.

My thinking was:

Why did the MCB's burn out in the first place, has this issue been fixed?
Is the new MCB damaged or faulty?
Possible cable damaged/snapped at consumer unit, due to age of cable?
Pest problems within house?
Are sockets with no power on a fused spur has the fuse gone and taken out the sockets?

Notional proposed fault finding:

Is MCB faulty?
Check connections and power at consumer unit, as is old wiring is something brittle/has the conductor broken during installation?
Ascertain that all sockets lost are on same circuit.
Continuity Test.
Insulation Resistance Test.

Any feedback gladly received, I will hopefully find out what the issue was third hand but am I along the right lines of things to consider?

 

[Pete999]

Initial CB burn outs possibly loose connections at the CB.
Some sockets not working, could be what you suggest.
What reading are shown on the certificate? probably not issued?
How did the insurance company determine that the CU was/is overloaded, was there an insurance company Electrician present at the time of the insurance inspection? or is this a case of some assessor who knows very little about Electrical Installations and due to the burn marks assumed it was overloaded.

 

[Marvo]

This is not my job and is an issue a colleague at work is having with his house wiring, but as I am doing my fault finding unit shortly will run it by you all out of interest to see whether I am thinking the right things.

A work colleague has come in today with the following problem:

He lives in a 1950's house and few weeks ago his consumer unit started smoking and three of the MCB's had burnt out, this took out the kitchen and dining room, he had the insurance company in due to the damage to the consumer unit and they refused to pay out as they say his board was overloaded. I am waiting for pictures of the old and new board and test results of installation out of interest.When you say it 'took out' the dining room and kitchen was there a house fire or did the circuits just go dead?

He employed an electrician who replaced said consumer unit with a new high integrity split board but has not rewired the property (Personally I think a rwwire this should have been considered given the age of the cable and the previous fault, he states this wasn't given to him as an option by the Sparks).I'd assume the sparky tested the circuits and visually inspected the wiring and deemed they were free from damage and faults. There doesn't appear to be a fault given for the burnt out MCB's over and above perceived continual overload.I'd fight the insurance company. A CU and the electrical installation in general is designed to handle overload conditions. They're a phenomenon that is expected to occur and the MCB's are specifically there to protect against it. In reality it's far more likely the burning was caused by a poor termination that became high resistance and generated heat but this is always difficult to prove conclusively because the damage that occurs is usually pretty extensive.

The sparks apparently finished last night and provided a test sheet, my mate plugged in his hoover downstairs and the MCB and RCD tripped immediately. Power has been lost downstairs and partially upstairs. He has re engaged the MCB and RCD which has stayed in but he still has no power to some sockets downstairs and some upstairs, he has called the electrician back but wanted to know my views.It could just be a faulty vacuum cleaner if the MCB tripped as well as the RCD. There may be a crossed or borrowed neutral issue but this wouldn't cause the MCB to trip, impossible to say without testing.

My thinking was:

Why did the MCB's burn out in the first place, has this issue been fixed?Most likely a poor termination
Is the new MCB damaged or faulty? Highly unlikely and difficult to test MCB's. If on the slim chance one trips intermittently and there's no fault present then just try a replacement. 99% of the time a tripping MCB indicates a fault
Possible cable damaged/snapped at consumer unit, due to age of cable?Age isn't really a factor unless it's rubber insulated wiring. Any damaged or snapped wiring would be easily visually identifiable.
Pest problems within house?Pest infestations such as ants or even mice could cause an MCB to malfunction and possibly even burning but highly unlikely unless there's a known pest problem. Also easily visually identifiable
Are sockets with no power on a fused spur has the fuse gone and taken out the sockets??? not sure what you're asking

Notional proposed fault finding:

Is MCB faulty? assume it's not unless there's visual damage
Check connections and power at consumer unit, as is old wiring is something brittle/has the conductor broken during installation?
Ascertain that all sockets lost are on same circuit.
Continuity Test.
Insulation Resistance Test.
PAT test vacuum cleaner

Any feedback gladly received, I will hopefully find out what the issue was third hand but am I along the right lines of things to consider?

See text in red.

 

[hightower]

Did the three MCBs burn out individually or was it one MCB burned out and burned the MCBs either side making it three? What side of the MCBs did it happen on (supply/load)?

Looking forward to seeing the photos.

 

[rolyberkin]

Thanks for the reply, am interested in common faults and issues .

He initially Just lost the power to the kitchen and dining room.

My concern is that he has re set the MCB and RCD yet some sockets are now still dead indicating a loss of power, hence why I was thinking about a damaged MCB or broken conductor. I would love to go and fault find but have told him to speak to the bloke who has done the work.

 

[rolyberkin]

Did the three MCBs burn out individually or was it one MCB burned out and burned the MCBs either side making it three? What side of the MCBs did it happen on (supply/load)?

Looking forward to seeing the photos.

Unfortunately I don't know, he has promised me some photos so will share as and when they come. I would suggest that it was one MCB and has then affected the two either side of it. Itching to stick my nose in!