Cant help you with the inverter other than read the manual for any ideas but as to the the plug on the top of the spindle I removed the end cap and removed the socket and then drilled for a cable gland and hard wired the wires in with a good earth connection with 1.5mm2 cable to the inverter ..
The plug and socket doesn't look good to be carrying 5-8 amps at 240v
Ian