I have 4 X MPPT 100/20's going to a fuse box. Cable run 0.5m. Each input to the box is fused separately. What wire size and fuse should I use? I was advised 40A on each input, but this seems too high??
What wire size should I use from the fuse box to the battery? Cable run 2m.
On the input to each MPPT 100/20 are 2 x's 115W panel wired in series. The circuit goes through an isolation switch. The systems is on a boat.
Do I need fuses PV to MPPT? What size?
Is there a general rule of thumb?
On a lot of DC wiring the fuse is mainly to protect the wire in case of short circuit.
As the 100/20 can accept 6mm cable, I would use 4.5-6mm. Considering 4.5mm cable is normally rated to around 50A, I would say a 40A fuse would be fine.
From the fuse box to the battery, the minimum I would use is 16mm cable with a 100A fuse. If you plan to use the fuse box for other devices in the future I would suggest going to 35mm cable or even larger and fused 10-25% below the cable rating.
Fusing of solar panels can be a whole discussion on its own and I will leave that for someone else to advise you on, it will depend on where you are mounting them, what protection the cables have, and a lot of other factors. In my motorhome I have dual pole breakers for the panels near the MPPT’s, but they don’t really protect much if the panel wiring was to get damaged.
