I allowed 360 watt per card when I chose my psu's I am running 6 R9 280x on 1 rig and 2 on another
So if you say 360w x 5 cards = 1800w plus what ever you will use for your cpu or ssd etc
If you take my rig that runs at 2000w and say 6/2000 = 333.333333 you could go 5 x 333.33333 = 1666.665watts
I have read that these cards will only pull 300 watts per card though, but my 6 card rig pulls ave 1950 - 2000watts, but I use an ssd drive and a 54watt cpu, and use powered riser cables.
Hope this helps, may be go with 2 x 850 psu's
Voltage in North America is between 110 and 120 so a 15A circuit have a max output of 1800W AC. I have heard of people running 4 280X on a 1200W PSU. Undervolting 5 cards will reduce the draw by 100W and in conjunction with 90% efficient PSUs, it should be at about 80-85% of 15A limit.