Breaker keeps blowing.. Help!

[Stopstalking]

Hi. I spent ages laying flooring in the loft, I decided to use one very last screw and screwed through the cable for the lighting!
I have cut the damaged part and reconected with a junction block, but soon as I throw the breaker, it trips. I have taken every single bulb out, but still does the same. If I disconnect the wire where I reconnected, it works fine and every other bulb works!
I then reconnect the broken wire and straight away trips, even without a bulb, and wall switch off!.
I have checked the wiring to make sure I connected it right a dozen times. No one has any idea what to check now!!
Please help!!

 

[PrenticeBoyofDerry]

Can you upload a picture of the cables?
Are sure you have not damage cables further downstream of this joint/damage?
What device is that trips (MCB or RCD)?

 

[Stopstalking]

I'll upload later, it's mcb that's blowing. Unless I damaged the cable further down last week when I did the rest Of The wiring. Just seems odd it's stop working today

 

[theprinceofdarkness]

Switch of the circuit and try to isolate that piece of cable, starting at the fuse box. Once the cable is disconnected from the live supply, you can use a meter to find the fault. If you are "blowing" (I hope tripping) a 5 A device then the resistance between the live and the neutral or earth will be low, so you may find it just with a bell and battery.
I have come across cables with multiple faults in, often down to mice or bad bodges on installation.
Frank

 

[PrenticeBoyofDerry]

I'll upload later, it's mcb that's blowing. Unless I damaged the cable further down last week when I did the rest Of The wiring. Just seems odd it's stop working today

I look forward to the pictures, If you can show the cable cores, terminals and the device that is tripping at the fuse board, that would be helpful. It would be handy if you also acquired a multi-meter so some testing can be made. But they do not perform all the tests that could be required to establish the fault that is causing the trips.
Please confirm this was the only electrical work carried out, there has been no other electrical work done during the recent period.
Also I must point out to you, that there are regulation in place, regarding the depth of cable in floor voids. If you have (which it sounds like you have done) laid loft boards over cables creating a void/hiding cables within a floor, it is very likely that the depths required or the addition protection needed by building regs have not been applied/amended to.