Fusing Solar Installation

MrWizard wrote:
I dont think its needed
i have almost 700w my fusing is at the input to the controller,
NOT on each panel

I guess my primary question is why fuse the input side of the controller at all. If the fuse is sized large enough to handle the peak power output of the panels, it will more than likely be large enough it won't blow even with a dead short. There isn't really any "Current pool" waiting in solar panels to dump in the case of a short like there is in a battery, or other type power supply. Being a PWM type controller, when the batteries demand it, the controller pretty much passes full panel output straight to the batteries anyway with the possible current flow going up less than an additional amp per panel under dead short when you take the battery resistance out of the circuit. On the output side of the controller, you could get a large current flow from the battery back to controller if something shorted in the controller, so it makes sense to me to fuse there, I just can't envision any situation on the solar panel side of the circuit where a fuse would protect anything, or add any safety to the circuit.