I think "BC GND-" means Bus Capacitor(-) for the VFD motor drive PCB pic shown Clough 42. That is for the primary HV bus, after the mains bridge rectifier.
What it means for the Jaycar lab power supply though must be different... the pic shows it right near the LV secondary terminals which would be very dangerous spacings if "BC GND-" goes to the primary MOSFET source after a sense resistor. You'd have to follow it back the PCB trace. It could be for EMI with C101,102,103 connecting the two grounds.