I set up a Norco 4224 for backup purposes and plugged in a couple of 3TB WD green drives, and have not had any issues at all. Maybe the WD green drives don't require as much current as these ones?
Temperature can be just as important as current draw. The amount of current those MOSFETs can handle will reduce fairly rapidly as ambient temperature increases and green drives tend to run much cooler than high speed 7200rpm drives.
We actually used to use Samsung EcoGreen drives in order to get more storage for cheaper, since our main use was backup: write once, read maybe. Unfortunately there don't exist 5400RPM 3TB drives; if they were as cheap as the 3TB Seagates, we'd buy them for sure. The 5400 rpm Ecogreens used to be the cheapest 2TB drives on the market by a large margin.
I never expected that paying more for a slower drive (but better power and less power-related issues) would actually make sense!
