Outdoor security light,electrical question?

My dad was trying to replace an outdoor security light which is on our shed.



The power cable comes in at the inside of the shed floor, then goes up the wall into a box with two fuses which have switches on.



One cable comes out of the fuse box to a double plug socket and the other comes out of the top to the security light outdoors.



Before he started to change the light he turned the power to the light off by the switch on the fusebox.



When he was changing the light, the houses main electricity tripped and everything went off.

There was no power coming through the wires as he tested the exposed ends with an indicating screwdriver.

Just to be doubly sure he took the fuse with the switch on out of the box but it tripped again.

How could it trip the main box if there is no power coming through?



I'm sorry if my description or electrical terminology is a bit off.



Any ideas please? Any sparks out there?



Thanks.Outdoor security light,electrical question? By removing the fuse from the light cct you have disconnected only the 'live'. He undoubtedly made a contact between neutral and 'earth' in doing the changeover.

If your main (house) switch has an RCD built-in, then that would have tripped it..



Outdoor security light,electrical question?The only thing that I can think of is the fuse box was wired incorrectly by having the Neutral commonly white being disconnected instead of the Hot commonly black, red or blue. If you have a light that is not grounded correctly and the neutral is broken by a fuse box or switch your meter will show no voltage unless you test the wires to ground. That is the only thing that I can think of to cause the problem that you are having.



I must say you should never trust a voltage indicating screwdriver, tick tracer or meter unless you test it on something that you know is hot first, you must do this always. I am surprised that there was not a %26quot;shock%26quot; involved with this electrical adventure. Outdoor security light,electrical question?sounds like he shorted the earth to either the neutral or live.



the RCD would still detect this, even though the circuit of switch off.



its of no real consequence, but you dont want to keep doing it as eventually it'll wreck the RCD