Ah, yeah, the N7 was supplying the power to the phone ... not all microUSB connections are as peculiar as that on the N7.
Some folks report N7 charging requires shorting the data pins on the cable / charger, others says a particular resistor is all that is required. Some say that there is charging but that the shorting is required for the "Charging" indicator to display on the N7. Some say slow 'USB' type charging via a split cable is doable, others say the code allowing it must be included (root required). All in all, a thoroughly confused situation.
My pitiful experiments using a powered hub, etc, show that if a OTG cable is used, you can not charge and if a OTG cable is NOT used, charging works but you can not transfer data.