I have a three circuit solar array. Live off the grid. Each is 48 volt rated but two are really 90 volt rated (3 x 250 watt x 24 volt which are really 30 volt). The other is more like 60 volt. (2 strings of 4 80 watt panels x 12 volt -really 17.5 volt - total 640 watts. I have three + armored cable (3 wires plus a bare ground) - Tec cable #6. Why can't I run three circuits - using the three insulated wires - with the bare copper as the common neutral? The armor acts as the ground.