There IS an electrical connection from the motherboard to the riser, period. An 'electrical engineer' that says otherwise is an idiot. As I said, if you measure the outer pins of the USB connector coming from the motherboard PCI-E slot connector with a multimeter while the motherboard is on you will see there is 3.3V coming from the motherboard PCI-E slot through the USB cable to the riser. If you plug in the USB cable coming from the x1 riser connector to the riser and measure the voltage on the two pins on the bottom of the riser circled in yellow, you will see this 3.3V IS passed to the riser. If you look at the traces on the bottom of a Version 006/008 riser you will see the traces from the supplemental power connector and the traces from the USB connector are connected, which is why you should only power the risers with the same PSU connected to the motherboard, so the voltages can be regulated according to a single source. As the PCI-E specification clearly states, the power source to the x16 PCI-E slot DOES NOT have to be on the same rail as the power source to the 6/8 pins connector on the card.



How much power is drawn from the PCI-E slot depends on how the card is configured by the manufacturer, not how you set up your PSU's. A card mining WILL pull between 35-55 W through the riser, depending on how it's configured and how much power is needed. Dual mining also causes more power to be pulled from the riser.