MidNite Solar Surge Protection Device MNSPD300DCThe MidNite Solar Surge Protector Device (MNSPD) is a Type 1 device per UL1449 rev3. It is designed for both AC and DC systems and provides protection to service panels, load centers or where the SPD is directly connected to the electronic device requiring protection. Protection for Classic and other charge controllers, off grid PV combiners and 120.240 VAC circuits.The DC SPD will work well on all DC circuits up to 300 volts as well as any 120.240 VAC circuits. The difference between the AC and DC SPD is the way the LED's are powered. The protection side of things is identical.FAQI ordered the MNSPD300DC. Why does my unit say MNSPD300AC? All units are labeled MNSPD300AC, however, the marking on the box indicates whether the unit is AC or DC. All units are compatible with both AC and DC systems regardless of the box markings, the only difference is how the indicator lights work. Each unit has several lights and a DC unit hooked up to a DC system will power all of the indicator lights and vice versa; an AC unit hooked up to an AC system will power all of the indicator lights. If you hook a DC unit to an AC system, however, only 1 of the indicator lights will work and vice versa, but the unit will still be safe and function properly.Why aren't all my lights on the MNSPD300 working? When you try and connect the MSNDP300AC on a DC circuit or vice versa, only 1 LED will illuminate, however, the MNSPD300 is still fully functional. In order that all of the lights work, you would need to connect an AC unit on an AC circuit and a DC unit on a DC circuit.