in the first part, there was current flowing even the switch is off, why? and can this be use by plugging to house board and use it as extension board?
That happens when your phase coming in neutral (here black wire) so when you connect phase to your main connection see that it should go through your extension board switch. Yes it can be use as extension board.
Output wire phase , neutral and ground of board connect to your house phase, neutral, ground . Try with safely by switching MCB off and testing with tester.
Let me explain We have main black cable of 3 wire through which 250v are coming which has Red-Phase,Balck-Neutral and Green-Ground .ok On the socket it's written L-phase N-Neutral and for Ground-G or earthing symbol. Switch has Two terminal. So the phase wire Red from main cable should go through one part of Switch so you can control it and other part of switch goes in the phase part of 3pin socket with wire. And Ground and Neutral wire are directly connected to the 3pin socket. For led indicator it is already connected in socket. If not then It is connected to phase and Neutral of 3pin socket. So whenever you press the switch the current will flow in Circuit and your Circuit will complete. 👍 If any problem comment below Thank you
Just check if ur phase is coming in right side of socket if it's not coming in right side then u have interchange Phase and Neutral . Try to check with Tester don't touch directly. High voltage AC is dangerous Thank you Take care👍