Tapping into lighting circuit keeps tripping MCB

[waheed357]

Hi,

I am hoping to get some help. I am trying to tap into my lighting circuit for a mirrored cabinet. Havent received the cabinet so just wiring for it now. However, when I connect a wire into one of the live lighting wire in the loft, the mcb stays tripped but when I disconnect the wire for the mirror, I can reset the mcb fine. Its a brand new wir. Is there a reason for this tripping as I cannot figure it out. I've drawn a simple photo. Wires 1 and 2 is the same wire i'm tapping into and 3 is the wire to mirror. 1 photos is of the 3 cables attached and the last is the one hanging for the mirror. I will sleave the earths as this is just to find out what is causing the trip. Help please.

 

[ETAF]

How do yo know that’s a lighting wire in
How Was it before you touched it
It’s not a switch is it
Have you tested the cable at all nothing in the wire shorting out
Is it new wire
What is at the other end have you used a 3 way wag at the end shorting

 

[flameport]

The end of the new cable has all 3 conductors shorted together in that single connector,

 

[waheed357]

oh my god, I am so stupid. Not sure how I missed that. Thank you.

 

[waheed357]

The end of the new cable has all 3 conductors shorted together in that single connector,

Its marked as upstairs lighting circuit in CU. When tripped the wires are not live

 

[waheed357]

oh my god, I am so stupid. Not sure how I missed that. Thank you.

oh my god, I am so stupid. Not sure how I missed that. Thank you.