Yeah, I have a Sorc, I've used Overload before, but I have no idea where this third ability bar comes from.
@ArchMikem Overload is a third bar. By default it will inherit everything on one of your bars, but when you start swapping skills around, you may notice your Overload skill bar doesn't change. Unless ZOS has changed it since the last time I had overload slotted, it is, in fact, a third skill bar. The only way to access it is to equip overload and activate it.