Like everyone is saying in here you need to plan according to what you are gonna be implementing in facility.
At a very minimum I would say about 200 watts per cab, and that is low. With avg rack densities and device's power needs these days you need to consider going higher then even that.
If you already know what is going in the rack or can get information on a particular device that would dominate your racks, you can get their general power information (amps & voltage) and use this
Amps to Watts Calculator made for data center related devices