Yesterday the MCB to my ground floor sockets tripped and everytime we go to put the switch back up it seems to cause a big spark and trip again. At one point it blew the main fuse which is located outside the consumer unit and comes before the electricity meter. We have replaced that fuses but the same thing keeps happening. The circuit wasn't being overloaded at the point it tripped as most of the items were off which is significantly less then what load is usually put on the circuit. Now we can't put the MCB switch back up and so have no power on the ground floor. Can anyone suggest anything I can do to make it work?
MCB Sparking
- Thread starter bhavikmithani
- Start date
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It is most likely a damaged cable, remove every socket, carefully inspect the cores for insulation damage and use sleeving to cover any damage. Make sure all entries have grommets and that cables aren't trapped under screws.
when that is all done test to make sure there are no shorts (prefferablly with an insulation resistance tester but a mulimeter is better than nothing) before reconnecting the circuit.
when that is all done test to make sure there are no shorts (prefferablly with an insulation resistance tester but a mulimeter is better than nothing) before reconnecting the circuit.
would it be necessary to check the wires under the floorboards aswell or just near to the sockets?
bhavikmithani said:
Yes it will be if there is no visible damage behind sockets.
Most common cause is a new screw fitted in a wall or a floor so look around any places where holes have been drilled or nails hammered in.
How did you replace the main fuse before the meter ?. That is something you should NOT touch, only the electricity supply people should touch that. If that main fuse has blown then there is every possibility that the MCB will have been damaged and will need to be replaced. The MCB should disconnect power long before the main fuse blows so it would appear the MCB has failed in the closed (power ON) position and no longer offers any protection.
I would STRONGLY recommend you get an electrician to inspect and repair as necessary.
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There has been no new screws or nails in the walls. We were recomended by an electricain to go and buy a new fuses and replace it. I did think that it should be done by the electrical company but they refused to do it saying that it was an internal house fault and nothing to do with them. I will check the wiring behind the sockets today and replace the MCB with a new one. The electriain recomended that i should rewire the whole ground floor with new sockets but as this would be extremly expensive i'm checking for problems before i go ahead with the rewiring
the MCB might have been damaged and need replacing. They will safely break a very large current, but, if it is big enough, maybe only once.
I concur with damaged cable. I assume all your appliances go through fused pugs, so the fuse would blow if it was an appliance at fault.
Any work that has been done recently should be suspected, especially nails or screws into walls or floors and even more so, any wiring changes or new sockets.
There is a possibility a wire has come loose inside the consumer unit, but this should be obvious when the cover is opened.
OOI. can you post a pic of the consumer unit, and the place where you changed the fuse? It might spark up other ideas.
bah, too slow
I concur with damaged cable. I assume all your appliances go through fused pugs, so the fuse would blow if it was an appliance at fault.
Any work that has been done recently should be suspected, especially nails or screws into walls or floors and even more so, any wiring changes or new sockets.
There is a possibility a wire has come loose inside the consumer unit, but this should be obvious when the cover is opened.
OOI. can you post a pic of the consumer unit, and the place where you changed the fuse? It might spark up other ideas.
bah, too slow
that is the consumer unit we have. the MCB that blew was the second one left of the two red switches.
I don't have a picture of where i replaced the fuse because i am at work at the moment, but i think its a 45amp fuses that connects the main supply from the electricity board to the consumer unit
aptsys said:
Like what?!?
Have you removed/unplugged all appliances from the socket outlet circuit.The MCB is possibly operating before a plugtop fuse somewhere.
Or could be some vermin damage under the floor/in a roof void??
This really needs checking professionally if the cause is not obvious (like an appliance) as an Insulation Resistance tester is likely to be needed.
Or could be some vermin damage under the floor/in a roof void??
This really needs checking professionally if the cause is not obvious (like an appliance) as an Insulation Resistance tester is likely to be needed.
I was thinking, supplier's fuse is not going to be faster than the plugtop, even though the MCB may be.
But good idea to unplug them all anyway. Also, maybe you'll spot a charred and melted socket while going round.
But good idea to unplug them all anyway. Also, maybe you'll spot a charred and melted socket while going round.
Am I the only one concerned that a DIYer has replaced the DNO fuse?
Supprisingly, the fuses are nice and easy to come by at my wholesaler 
The OP may have replaced the fuse as he believed it to be within his realm.
Speaking with the DNO (or more likely the supplier of your lecky) can result in very poor mis-information. If the OP kept telling them about his MCB that keeps tripping, and only mentioned another fuse once..........
The OP may have replaced the fuse as he believed it to be within his realm.
Speaking with the DNO (or more likely the supplier of your lecky) can result in very poor mis-information. If the OP kept telling them about his MCB that keeps tripping, and only mentioned another fuse once..........
@ the OP, I feel an overwhelming need to say the following:
1. The fuse in the box before the meter, with the big wires in it, IS NOT YOUR PROPERTY! It should have labels all over it, to this effect! You are NOT ALLOWED to open it up and change the fuses! Only the people it belongs to (your DNO) are allowed to do this, and you have broken the law by doing it. On mine there is a DANGER OF DEATH sticker on it. I'd take heed of this if I were you. The older ones can be VERY fragile and if there's any load on them they will arc and probably kill you.
2. Your DNO is not responsible for the condition of your house wiring, no matter if you blew their fuse or not.
3. If it really was a 45 amp fuse, it is woefully undersized. Standard nowadays is 80-100 amps. Again, ASK YOUR DNO to replace it for you.
4. That picture you showed us is a generic picture. Every consumer unit is different. Yours probably has different rated breakers in it, because your house will have different circuits, even to your next door neighbour.
5. NEVER come on this forum and put money before safety.
1. The fuse in the box before the meter, with the big wires in it, IS NOT YOUR PROPERTY! It should have labels all over it, to this effect! You are NOT ALLOWED to open it up and change the fuses! Only the people it belongs to (your DNO) are allowed to do this, and you have broken the law by doing it. On mine there is a DANGER OF DEATH sticker on it. I'd take heed of this if I were you. The older ones can be VERY fragile and if there's any load on them they will arc and probably kill you.
2. Your DNO is not responsible for the condition of your house wiring, no matter if you blew their fuse or not.
3. If it really was a 45 amp fuse, it is woefully undersized. Standard nowadays is 80-100 amps. Again, ASK YOUR DNO to replace it for you.
4. That picture you showed us is a generic picture. Every consumer unit is different. Yours probably has different rated breakers in it, because your house will have different circuits, even to your next door neighbour.
5. NEVER come on this forum and put money before safety.
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