I replaced a MCB with a RCBO today for socket circuit in small factory unit. I tested it all and it was fine. After i left there was a bang in the CU and the power went down, blowing two of the three main fuses (3Phase). Upon investigation there seems to be soot on the new RCBO which is red phase and yellow phase next to it which is spare. Any suggestions what could of caused this as i've checked all connections and turned the main switch back on and it seems to be sp[arking, so ive isolated and left off for now
CU Problem
- Thread starter New2Game
- Start date
Sponsored Links
-Did you check that the RCBO was correctly installed eg no wires trapped etc?
-What state was the rest of the board in?
-Was the circuit in use when the 'bang' happened?
-What size are the main fuses?
As you have blown two phase fuses then the chances are the fault is in the board especially as there is soot on the RCBO.
If you are 'new2game' then if you are in any doubt about your ability to sort this out as it involves 415V then seek the help of a competant, more experienced 'friend'.
You might end up having to insulation test the board (obviously with isolation carried out, RCBOs removed etc)
You must be thoroughly competant to do this.
-What state was the rest of the board in?
-Was the circuit in use when the 'bang' happened?
-What size are the main fuses?
As you have blown two phase fuses then the chances are the fault is in the board especially as there is soot on the RCBO.
If you are 'new2game' then if you are in any doubt about your ability to sort this out as it involves 415V then seek the help of a competant, more experienced 'friend'.
You might end up having to insulation test the board (obviously with isolation carried out, RCBOs removed etc)
You must be thoroughly competant to do this.
Clearly whatever happened here doesn't sound like an earth fault, as this should have simply tripped the RCBO and caused no damage. That is, assuming you've checked the breaking capacity of the device you fitted is of a suitable rating.
Presumably the circuit worked fine before the RCBO was fitted, so it's only fair to assume you've caused the fault. Perhaps you disturbed some wiring and allowed two phases to come into contact with each other - were the blown fuses on red and yellow by any chance?
Either way, as an electrician undertaking this sort of work you really should he able to locate the fault on your own. When you do so you might also want to consider a replacement RCBO!
EDIT: Damn, beaten!
Presumably the circuit worked fine before the RCBO was fitted, so it's only fair to assume you've caused the fault. Perhaps you disturbed some wiring and allowed two phases to come into contact with each other - were the blown fuses on red and yellow by any chance?
Either way, as an electrician undertaking this sort of work you really should he able to locate the fault on your own. When you do so you might also want to consider a replacement RCBO!
EDIT: Damn, beaten!
Borrowed neutral?
RCBO carrying neutral current for another circuit or phase - causes a huge imbalance of current, which tripping does not stop and which induces much more current in the sense coil than it can handle - BANG - been there, done that!
It sounds like somewhere on the circuit, the neutral from the RCBO protected circuit has been used to provide the neutral for a circuit on a different circuit or phase.
RCBO carrying neutral current for another circuit or phase - causes a huge imbalance of current, which tripping does not stop and which induces much more current in the sense coil than it can handle - BANG - been there, done that!
It sounds like somewhere on the circuit, the neutral from the RCBO protected circuit has been used to provide the neutral for a circuit on a different circuit or phase.
Sponsored Links
When you have connected the RCBO it hasn't broken something and moved the busbar causing two of them to short together? It shouldn't really happen but you never know. What make of distribution board? Is it the correct RCBO for the board? Did it go together nice and easily or did it take a bit of brute force?
Its a merlin gerin. it had stands of copper from 10mm cable between screw on busbar and mcb so used the same when swapped for rcbo, do you reckon one of the strands may of fell and arched across phases?
It was between red and yellow, why did you ask?
It was between red and yellow, why did you ask?
electronicsuk said:Presumably the circuit worked fine before the RCBO was fitted, so it's only fair to assume you've caused the fault. Perhaps you disturbed some wiring and allowed two phases to come into contact with each other - were the blown fuses on red and yellow by any chance?
Why u ask yellow n red?
It depends how damaged it is. Is it an ISObar type? Remove any item which is vulnerable to IR testing before carrying out an IR test, RCBOs can fall into this category. I'm thinking if it is in the bus bar chamber then it will be easier to replace the bus bar.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
