Main fuse blows when sub-box energised

[zippy]

Old wylex system, main fuse box with ring & lighting and small 3-fuse sub box with shower, oven and secondary ring. All rewirable fuses. Main fuse blown when sub box powered, dno replaced bullet fuse that immediately blew again when sub box powered so dno replaced again and left sub box off. None of the rewirable fuses blew on either occasion, sub circuits had no load either both times.

Scratching head why dno fuse blew but all consumer fuses intact, any ideas e.g. is fault more likely to be with sub box because of this?

Worried about firing up any of the 3 sub circuits if dno fuse keeps blowing, would a 6amp plugin mcb trip before the dno if fitted just for my testing?

 

[Simonslimline]

The bang test is probably not the best way to resolve this lol.

Some proper testing perhaps?

 

[Leesparkykent]

Old wylex system, main fuse box with ring & lighting and small 3-fuse sub box with shower, oven and secondary ring. All rewirable fuses. Main fuse blown when sub box powered, dno replaced bullet fuse that immediately blew again when sub box powered so dno replaced again and left sub box off. None of the rewirable fuses blew on either occasion, sub circuits had no load either both times.

Scratching head why dno fuse blew but all consumer fuses intact, any ideas e.g. is fault more likely to be with sub box because of this?

Worried about firing up any of the 3 sub circuits if dno fuse keeps blowing, would a 6amp plugin mcb trip before the dno if fitted just for my testing?

Why not take the cover off and visually inspect the internals?

 

[davesparks]

Well you shouldn't have any need to worry about 'firing up' any of the circuits because you won't be switching them on until you have found the fault and repaired it will you?

Get your megger out and carry out appropriate testing to find the fault. There is a massive hint in your OP as to where the fault could be and it could take all of ten minutes to find the fault, but without further useful information it's impossible to tell.


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[Octopus]

Got to be a wind up........

 

[Marvo]

.........would a 6amp plugin mcb trip before the dno if fitted just for my testing?

Are you thinking about doing live tests??? Given the problem I'd imagine even a cursory risk assessment would rule live tests out. Do the dead tests!!!!

**edit** Got beaten to the post by 4 people this time. I think I need typing speed lessons.

**edit/edit** Thanks for keeping it civil everyone.

 

[davesparks]

**edit/edit** Thanks for keeping it civil everyone.

Well it has stretched me to the limits of my self control so far to keep it civil!

 

[sparksburnout]

I've just looked back at your posts, and yes my darkest fears have been confirmed, you are actually working for paying customers as an "electrician" . God help us all. Maybe you could get the DNO back in for a bit of assistance?

 

[Marvo]

The consensus seems to be that making anything live before carrying out a full range of dead tests is out of the question so your question has been answered. Even pursuing the idea in the OP any further is pointless so I'm closing this thread.