31.01.2018 16:40 start /
Thank you all for the answers, because this is not a standard wiring plug, i need assistance wiing the wifi adapter in the middle of cable which connect the energy master expert lcd display to the energy master expert plug.
Is this correct?
WIFI ADAPTER LIVE IN = Energy master expert PLUG BROWN live wire
WIFI ADAPTER LIVE OUT = Energy master expert LCD DISPLAY BROWN live wire
WIFI ADAPTER NEUTRAL IN = Energy master expert PLUG BLUE neutral wire
WIFI ADAPTER NEUTRAL OUT = Energy master expert LCD DISPLAY BLUE neutral wire
WIFI ADAPTER EARTH IN = Energy master expert PLUG BLACK wire
WIFI ADAPTER EARTH OUT = Energy master expert LCD DISPLAY BLACK wire
\ end 31.01.2018 16:40
31.01.2018 16:36 start / Update from customer service:
**The Ground Line is bridged in the connector
The meter does not require a Ground Line in the cable.
Blue is the Null Line and black and brown are the Live Line
Should you have further questions, please feel free to contact us via email.
Yours sincerely
ELV Elektronik AG
Technical customer service department** \ end 31.01.2018 16:36
Which colors are Ground Line, Null Line and Live Line?
The standard says the Ground line is always green-yellow.
None of these wires is green-yellow. Thanks.
update
If black is Earth, then why the on off switch button is using the black wire? 
Because the cable is too short , less than 2 meters, i want to extend it. I also want to join the cables with a wifi adapter SONOFF® POW 16A 3500W DIY WIFI Wireless Long Distance APP Remote Control Switch Socket Power Monitor Current Tester For Smart Home 80-160MHz AC 90-250V Support 2G/3G/4G Network.
That is why i need to know exactly which colors are Live, Null and Earth.
Best Answer
This is a combined plug/socket. The ground prongs are connected internally, no wire needed. You have to connect the blue wire to the (also internally connected) neutral screw. The brown and black wires go to the other plug/socket screws, it's live in/live out.
simulate this circuit – Schematic created using CircuitLab