The utility interactive 15kW PV system we are designing will have enphase S280 microinverters. There will be an AC combiner panel. We plan to put an AC disconnect switch (100 Amp rated) next to the meter box. There are various options for the disconnect: fused or non-fused, 2 or 3 pole.

1- Fused or non-fused?

2- 2 pole is enough, but is there any reason why we cannot use a 3-pole safety switch by: either leaving one pole unconnected, or using the 3rd pole for disconnecting neutral wire. I am asking this because many brands seem to have only 3-pole options for non-fused general duty safety switches, or when they have a 2-pole option, they just connect one of the poles directly (effectively re-using the 3-pole design).

Some examples:

http://www.amazon.com/Siemens-HNF263R-600-volt-Non-Fused-Switches/dp/B005G9556E

http://www.homedepot.com/p/Square-D-100-Amp-240-Volt-3-Pole-Non-Fusible-Outdoor-General-Duty-Safety-Switch-DU323RB/205071153

http://www.homedepot.com/p/Siemens-General-Duty-100-Amp-240-Volt-2-Pole-Outdoor-Fusible-Safety-Switch-with-Neutral-GF223NR/205623366