So just now I was adding an extra light over my day bed it's a vintage 60 watt bulb looks like an old radio valve it even has the little glass pip on top. Anyhow as I was wiring it up two whiskas of wire touched there was barely any sound but it popped the 5 amp fuse in the plug adaptor and tripped 16 amp MCB how is this even possible even under partial short circuit conditions surely a 5 amp fuse should clear before a 16 amp MCB?
I just did a quick selectivity study and the fuse should have beaten the MCB as in theory full selectivity is achieved. But that is only theoretical and in realatity, as you have proved, theory is based on variables not all of which can be quantified. I have seen recently a sparks drilling a hole in trunking hit a cable inside and blow the MCB on the board and the MCCB back at the main panel. He also needed a new drill bit.
We used to hold the cables away from the drill site with some cardboard, wood or a small length of plastic mini trunking to prevent drill damage.
I just did a quick selectivity study and the fuse should have beaten the MCB as in theory full selectivity is achieved. But that is only theoretical and in realatity, as you have proved, theory is based on variables not all of which can be quantified. I have seen recently a sparks drilling a hole in trunking hit a cable inside and blow the MCB on the board and the MCCB back at the main panel. He also needed a new drill bit.
We used to hold the cables away from the drill site with some cardboard, wood or a small length of plastic mini trunking to prevent drill damage.
