Short Circuit
- Thread starter AlanW
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AlanW said:
I'm not sure I follow?
However wires shouldn't melt or smoke even under a short circuit condition - the fuse/breaker should stop that.
Can you provide more info i.e. How old is the wiring, what type of fuse did if have, how many cables ran into the socket etc etc.
Many thanks for your reply.
The wiring is about 20 years old and is the grey twin and earth. It did have a properly rated fuse with fuse wire, but not the modern breakers. However, it did not blow the fuse. It had 3 cables going into, 2 from the ring main and one spur going to another socket. There was a test on the circuit during the day and the electrician did open this socket and done something. Later that day, in the evening I could smell like a plastic burning and after a few minutes I found it. It was socket behind an armchair and there was smoke coming from it. I switched off the main power switch and took out the fuse and put the switch back on so I could have lights.
A section of wire was replaced at the point of the short to correct the fault and a new split consumer box fitted. Since then the ring main has been tripping a lot. But what I am trying to ascertain is: would the whole ring main be damaged, causing some break down of the insulation, or is it ok just to replace a section of it?
The wiring is about 20 years old and is the grey twin and earth. It did have a properly rated fuse with fuse wire, but not the modern breakers. However, it did not blow the fuse. It had 3 cables going into, 2 from the ring main and one spur going to another socket. There was a test on the circuit during the day and the electrician did open this socket and done something. Later that day, in the evening I could smell like a plastic burning and after a few minutes I found it. It was socket behind an armchair and there was smoke coming from it. I switched off the main power switch and took out the fuse and put the switch back on so I could have lights.
A section of wire was replaced at the point of the short to correct the fault and a new split consumer box fitted. Since then the ring main has been tripping a lot. But what I am trying to ascertain is: would the whole ring main be damaged, causing some break down of the insulation, or is it ok just to replace a section of it?
Sounds like a loose connection, not a short.
The spark must of loosend something by mistake.
Should be ok, but you could get a different spark to a pir on that circuit
The spark must of loosend something by mistake.
Should be ok, but you could get a different spark to a pir on that circuit
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But would the insulation melt and turn black for some distance down the cable with a loose connection? As this was the case and that cable had to be replaced before the tripping stopped. And would this not weaken the rest of the ring main insulation if is was a short and had not blown the fuse for quite a few minutes? What is a pir? Is it a test to check insulation or wiring.
Thanks
Thanks
You said it didn't trip??
Yes, a loose connection will allow heat from this llose connection(terminal) to conduct down the copper, melting the insulation as it goes. The heat wont damage more than a few inches usually.
Once the insulation has melted, it may then short to the earthed back box or similar, and cause the trip to operate - this is then a short.
Yes, a loose connection will allow heat from this llose connection(terminal) to conduct down the copper, melting the insulation as it goes. The heat wont damage more than a few inches usually.
Once the insulation has melted, it may then short to the earthed back box or similar, and cause the trip to operate - this is then a short.
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PIR - periodic inspection report.
So the electrian came before the problem appeared - what was here there to do - just inspecting or to do work?
A fault really shouldn't turn cables black. (Ok you drill through one etc it leaves a small burnt area but not a big one.) Loose connections can cause arcing and heat damage. It could also be a broken ring causing overload.
Its probaly worth checking all you sockets to ensure the cables are secure and tight and to see if theire is any other sign of damage.
I'd get another sparky to come and test the circuit. He should perform a visual inspoection, check the ring continuity, test the insulation resistance and perform a loop test to ensure disconnection times are ok.
So the electrian came before the problem appeared - what was here there to do - just inspecting or to do work?
A fault really shouldn't turn cables black. (Ok you drill through one etc it leaves a small burnt area but not a big one.) Loose connections can cause arcing and heat damage. It could also be a broken ring causing overload.
Its probaly worth checking all you sockets to ensure the cables are secure and tight and to see if theire is any other sign of damage.
I'd get another sparky to come and test the circuit. He should perform a visual inspoection, check the ring continuity, test the insulation resistance and perform a loop test to ensure disconnection times are ok.
The electrician came to do a pir before any electrical work was carried out. This was for a council grant. Maybe he found a loose connection at that time. However, the next sparky did wire up an extention and had to renew some of the old wiring including that fauly part of the ring main. He did have to come back several time and replace sections on that ring main that kept tripping until recently when the mbc would not go back on. If you did try to swicht it on it would go straight off with a bang under the floor boards. Now I have another sparky and he has just replaced some other sections of cable having found some faults, including a black cable with a hole in it. But what I really want to know is, if there was a short that lasted for about a minute without tripping, would this
damage the whole ring main?
damage the whole ring main?
too much current will damage the entire cable (i.e wiring a cooker with 1.5mm will fry it). however the MCB (or fuse) should be rated lower than the cable's max load so it doesnt get damaged. you should test the insulation of the cable just to make sure it isint damaged
I don't quite see what is going on here. I think you have said that you had two electricians. The first did an inspection, and then a few hours later the ring nearly caught fire. Then a second was called? Or did the first come back to see what had happened?
Presumably you got someone to see about the fire fault straight away. Then later the second man did the extension wiring and made some more repairs to the ring.
If a professional sparks came and repaired the ring after the smoke problem, I would have expected him to fix it properly. Yet he did not. You say that after this the mcb kept tripping. You do mean mcb (one of a row of switches) not RCD (big switch with test button built into it.. but not the main consumer unit switch)
Any circuit which trips the mcb as soon as it is switched on has a serious problem. Tripping of an RCD is more common and needs investigating, but it can be due to a much more minor fault.
Sounds as though your mcb trip was due to a direct short inside a cable. Best I can understand from all this is that there were at least two faults. The first due to something the first electrician did. The second sounds more like someone drove a nail through the cable. If they did, then this might be an intermittent fault. For example, when someone walked over the part of the floor where the nail was.
Alternatively, if the conductor inside a cable had somehow broken, then this could arc and burn through the insulation. If it caused enough damage the insulation might fail and then cause the mcb to trip from a direct short between two wires.
There are other possible interpretations. I can just about imagine that the first spark left a loose connection. I find it hard to believe that just this caused cable to burn, but this is possible. I find it easier to believe that this happened because the ring was now separated into two halves and most of the electrical load was now on one half. This could cause overloading and heating in itself of the cable. Possibly a bad contact was causing additional heating at this one point.
If the heating was due to a bad connection, then probably it would only be at this one place. If it was due to general overloading of a ring now split into two halves, then it might have affected cables generally.
If the circuit was extremely badly designed or for some reason the original fuse was failing to blow when it should, then the cable could have been damaged by this. It seems unlikely. Damaged cable from the first incident could certainly help explain a further incident. But any sparks repairing the first damage should have done a pretty thourough check to satisfy himself what had happened and that everything was now ok.
Sorry, hard to be helpful at a distance.
Presumably you got someone to see about the fire fault straight away. Then later the second man did the extension wiring and made some more repairs to the ring.
If a professional sparks came and repaired the ring after the smoke problem, I would have expected him to fix it properly. Yet he did not. You say that after this the mcb kept tripping. You do mean mcb (one of a row of switches) not RCD (big switch with test button built into it.. but not the main consumer unit switch)
Any circuit which trips the mcb as soon as it is switched on has a serious problem. Tripping of an RCD is more common and needs investigating, but it can be due to a much more minor fault.
Sounds as though your mcb trip was due to a direct short inside a cable. Best I can understand from all this is that there were at least two faults. The first due to something the first electrician did. The second sounds more like someone drove a nail through the cable. If they did, then this might be an intermittent fault. For example, when someone walked over the part of the floor where the nail was.
Alternatively, if the conductor inside a cable had somehow broken, then this could arc and burn through the insulation. If it caused enough damage the insulation might fail and then cause the mcb to trip from a direct short between two wires.
There are other possible interpretations. I can just about imagine that the first spark left a loose connection. I find it hard to believe that just this caused cable to burn, but this is possible. I find it easier to believe that this happened because the ring was now separated into two halves and most of the electrical load was now on one half. This could cause overloading and heating in itself of the cable. Possibly a bad contact was causing additional heating at this one point.
If the heating was due to a bad connection, then probably it would only be at this one place. If it was due to general overloading of a ring now split into two halves, then it might have affected cables generally.
If the circuit was extremely badly designed or for some reason the original fuse was failing to blow when it should, then the cable could have been damaged by this. It seems unlikely. Damaged cable from the first incident could certainly help explain a further incident. But any sparks repairing the first damage should have done a pretty thourough check to satisfy himself what had happened and that everything was now ok.
Sorry, hard to be helpful at a distance.
Yes 2 Electricians. The first one to test the circuits and the second to do the job. It was the second one that wired the exstension and "repaired" the fault to the existing wiring.
Later (within a few days) it was tripping on the RCD to point were he had to replace sections of wiring and then the RCD would stay on.
However, about 10 months later it started to trip again until it would not stay on. The same electrician came back and replaced more or less the same sections again and moved the circuit onto an mbc, saying it was a slight earth leak. He went away and later that day my daughter noticed that there was no power upstairs. apparently he had disconnected this section. I called him back and he put upstairs onto the RCD section. Upstairs and down stairs used to be on the same ring.
I suspect that he has now made the circuits radial (which answers your other point) rather than ring. I have now just had a 3rd electrician and he appears to have have worked on the ciruit more logically. He did find a blackened hole on a cable, perhaps a nail as you mentioned. He also found a junction box sitting in the wet. He also said that the back boxes were not earthed. This work he covered was also the same area that the other electrician covered. So this speaks volumes to me.
However, I am now concerned that the sections of cable that have not been replaced, might not be in a good state. Also, if upstairs and down stairs has been split into 2 radials, will it be safe enough?
I appreciate everyones help.
Later (within a few days) it was tripping on the RCD to point were he had to replace sections of wiring and then the RCD would stay on.
However, about 10 months later it started to trip again until it would not stay on. The same electrician came back and replaced more or less the same sections again and moved the circuit onto an mbc, saying it was a slight earth leak. He went away and later that day my daughter noticed that there was no power upstairs. apparently he had disconnected this section. I called him back and he put upstairs onto the RCD section. Upstairs and down stairs used to be on the same ring.
I suspect that he has now made the circuits radial (which answers your other point) rather than ring. I have now just had a 3rd electrician and he appears to have have worked on the ciruit more logically. He did find a blackened hole on a cable, perhaps a nail as you mentioned. He also found a junction box sitting in the wet. He also said that the back boxes were not earthed. This work he covered was also the same area that the other electrician covered. So this speaks volumes to me.
However, I am now concerned that the sections of cable that have not been replaced, might not be in a good state. Also, if upstairs and down stairs has been split into 2 radials, will it be safe enough?
I appreciate everyones help.
if it was a ring using 2.5mm cable and has now been split into 2 radials, it is dangerous as the cable can be overloaded and possibly cause a fire
EDIT: if they are on a radial using 2.5mm then it must be protected by a 20A breaker if the total wire length is less than 27M. if less than 33M it must be a 16A breaker (35M if a 15A fuse)
EDIT: if they are on a radial using 2.5mm then it must be protected by a 20A breaker if the total wire length is less than 27M. if less than 33M it must be a 16A breaker (35M if a 15A fuse)
People here sometimes get very uptight about electrical safety and DIYers. Myself, I think people asking questions here are the sensible ones who DO think twice before doing things which they do not know enough about. The really nasty stuff is when professionals who claim to know what they are doing make a total balls up. They may be really good electricians too, but everyone has terrible days when nothing goes right and there are 6 urgent things at once. Also, time is money, and how long can you faff around trying to figure what is wrong with the meter ticking?
Ok. Do you have a garden? I ask, because any socket which might power equipment outdoors should be on a RCD according to regulations. This would allow upstairs ring to be non-RCD, but downstairs really should be. I think you said that you have the opposite.
Some electrical equipment may have small earth leaks which can trip a RCD. This is annoying but not dangerous if the leak is small. But a RCD is designed to cut off power with very small current leaks to earth BEFORE they can grow into big ones. If you do have a problem with some device causing trips, then my advice would be to sort the equipment, not disconnect the RCD. There should NEVER be a RCD trip from a standard socket circuit with nothing plugged in. (unless something is wrong with it!)
Junction box wet could cause RCD trip. Exactly the sort of thing it is designed to detect. So it did exactly what it was supposed to...but then someone disconnected it for working correctly?
Non earthed back boxes is a bit of an argument. The official line seems to be that it is ok, provided the metal box has at least one fixed screw hole. Normally nowadays one hole is a fixed lug bent out of the box. The other is a slider which allows the socket to wobble a bit to get it straight. Provided there is at least one fixed hole, the screw through the socket plate makes contact between the metal earthed rivet hole on the socket and the box. Some people feel this is not adequate and a wire is needed between the plate and box.
You have not said what rating the breakers are on these circuits. It is possible to split a 2.5mm cabled ring into two radials, but not to then run them from a 32A breaker. It would have to be reduced. Alternatively, maybe someone has created two rings, but wired the lot onto the same breaker. Are there any spares?
How the hell does the guy 'forget' to reconnect a wire floating about in the consumer unit? OK, there are lots of wires inside, but you do seem to be having a lot of mistakes.
It is possible to test a circuit to check the insulation. You would do this with resistance meter at the Consumer unit end. I would imagine someone has done this by now, but who knows. Otherwise, removing the sockets allows you to inspect the ends of the cables and would show if they have obvious heat damage. presumably this has been done a lot by now.
It sounds as though enough faults have been found to explain things. I hope the cause of the wet junction has been found and fixed.
I can not give you a definitive answer on the cable. If they look ok, feel ok and test ok, then they would be considered ok. They will be degraded by heat, but they are also designed to withstand occasional accidents. Your case does seem to have given them a bit of punishment.
Ok. Do you have a garden? I ask, because any socket which might power equipment outdoors should be on a RCD according to regulations. This would allow upstairs ring to be non-RCD, but downstairs really should be. I think you said that you have the opposite.
Some electrical equipment may have small earth leaks which can trip a RCD. This is annoying but not dangerous if the leak is small. But a RCD is designed to cut off power with very small current leaks to earth BEFORE they can grow into big ones. If you do have a problem with some device causing trips, then my advice would be to sort the equipment, not disconnect the RCD. There should NEVER be a RCD trip from a standard socket circuit with nothing plugged in. (unless something is wrong with it!)
Junction box wet could cause RCD trip. Exactly the sort of thing it is designed to detect. So it did exactly what it was supposed to...but then someone disconnected it for working correctly?
Non earthed back boxes is a bit of an argument. The official line seems to be that it is ok, provided the metal box has at least one fixed screw hole. Normally nowadays one hole is a fixed lug bent out of the box. The other is a slider which allows the socket to wobble a bit to get it straight. Provided there is at least one fixed hole, the screw through the socket plate makes contact between the metal earthed rivet hole on the socket and the box. Some people feel this is not adequate and a wire is needed between the plate and box.
You have not said what rating the breakers are on these circuits. It is possible to split a 2.5mm cabled ring into two radials, but not to then run them from a 32A breaker. It would have to be reduced. Alternatively, maybe someone has created two rings, but wired the lot onto the same breaker. Are there any spares?
How the hell does the guy 'forget' to reconnect a wire floating about in the consumer unit? OK, there are lots of wires inside, but you do seem to be having a lot of mistakes.
It is possible to test a circuit to check the insulation. You would do this with resistance meter at the Consumer unit end. I would imagine someone has done this by now, but who knows. Otherwise, removing the sockets allows you to inspect the ends of the cables and would show if they have obvious heat damage. presumably this has been done a lot by now.
It sounds as though enough faults have been found to explain things. I hope the cause of the wet junction has been found and fixed.
I can not give you a definitive answer on the cable. If they look ok, feel ok and test ok, then they would be considered ok. They will be degraded by heat, but they are also designed to withstand occasional accidents. Your case does seem to have given them a bit of punishment.
Yes, I have a back and front garden and you are also correct in saying that the upstairs is on the RDC side and the downstairs on the MBC and it should be the other way round for safety purposes. Also, I have just found out that upstairs has been taken off the ring and put on radial.
I know this because I asked my son to take the cover off the CU (I am in a wheelchair so can't get down there) there is only one red wire going into the fuse for upstairs.
Downstairs has a brown and red wire were the electrician had extended the ring back to the CU with the new coloured cable. Also, the other tail of upstairs must be left under the floorboard some where? So, it means upstairs on the radial has 4 sockets in three bedrooms. One socket in each of the 2 small bedrooms and two in the master bedroom. However, I have three grown up children who like to have their own TVs video gaming machines and the usual, so do you think this will be ok.
I am not trying to knock any electrician here. I just want to know that I am not in any danger. With all this messing around, it would have been quicker to rewire downstairs. It is only 5 sockets
I know this because I asked my son to take the cover off the CU (I am in a wheelchair so can't get down there) there is only one red wire going into the fuse for upstairs.
Downstairs has a brown and red wire were the electrician had extended the ring back to the CU with the new coloured cable. Also, the other tail of upstairs must be left under the floorboard some where? So, it means upstairs on the radial has 4 sockets in three bedrooms. One socket in each of the 2 small bedrooms and two in the master bedroom. However, I have three grown up children who like to have their own TVs video gaming machines and the usual, so do you think this will be ok.
I am not trying to knock any electrician here. I just want to know that I am not in any danger. With all this messing around, it would have been quicker to rewire downstairs. It is only 5 sockets
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