Tripped lighting circuit

[Dewi]

Can anyone tell me why the following happened please?...... Basically I was wiring up some upstairs lights and had removed the fuse at the consumer unit for the upstairs lighting circuit. (The upstairs sockets and downstairs lights etc etc were still on with the fuse in.) I disconnected one of the original upstairs lights and found that the supply cables were too long for what I now needed, so I snipped through the 1.0mm T/E. You've probably guessed the rest - as I did this I tripped everything. I then proceeded to switch off completely at the main consumer unit to finish the job. It all worked out ok in the end but I'm confused why I tripped the main trip switch. I thought that as I had removed the fuse that protected the upstairs lighting circuit that I was working 'safely' - but obviously I was wrong. What was still live?

 

[Spark123]

Was it an RCD that tripped?

 

[andy]

Can anyone tell me why the following happened please?...... Basically I was wiring up some upstairs lights and had removed the fuse at the consumer unit for the upstairs lighting circuit. (The upstairs sockets and downstairs lights etc etc were still on with the fuse in.) I disconnected one of the original upstairs lights and found that the supply cables were too long for what I now needed, so I snipped through the 1.0mm T/E. You've probably guessed the rest - as I did this I tripped everything. I then proceeded to switch off completely at the main consumer unit to finish the job. It all worked out ok in the end but I'm confused why I tripped the main trip switch. I thought that as I had removed the fuse that protected the upstairs lighting circuit that I was working 'safely' - but obviously I was wrong. What was still live?

im guessing the main switch is an RCD. MCBs only disconnect live. not neutral and earth. so when you cut the cable, you shorted neutral and earth, enough for the RCD to detect. so it tripped.

 

[Dewi]

No, it was the main trip switch connected to the consumer unit, so it cut the power to everything.

 

[andy]

No, it was the main trip switch connected to the consumer unit, so it cut the power to everything.

again, is it an RCD?

(and a standard 'mains switch' is just an isolator. id be worried if that tripped....)

 

[Dewi]

It was an MCB.

 

[andy]

It was an MCB.

then you didnt switch off properly. was there a spark and holes in cutters after cutting cable? no? then i highly doubt it was an MCB.

oh, and double pole MCB's are rare for mains switches. and if it was a single way MCB, then it wont be the mains switch.

 

[Spark123]

What does the writing on the main switch say?

 

[Dewi]

I must have switched it off properly as I pulled the fuse out completely. My question is still - why did I trip everything when I cut through a cable that was in a circuit that was 'not live'? Should I have switched the entire consumer unit off ?? (with the 8 fuses in). There is no writing on the main switch.

 

[andy]

I must have switched it off properly as I pulled the fuse out completely. My question is still - why did I trip everything when I cut through a cable that was in a circuit that was 'not live'? Should I have switched the entire consumer unit off ?? (with the 8 fuses in). There is no writing on the main switch.

we need to know exactly what tripped. 'main switch' isnt much help. if your not gonna tell us what we need to know, dont bother asking. (pics would be useful)

and just because the fuse was remved, doesnt mean it was 'switched off properly'. did you do safe isolation? did you remove the neutral from the neutral bar? no? then it wasnt isolated properly.