Figuring Proper Fuse Size

Padlin wrote:
dual 6V batteries, 230A. 1500w Inverter, 125A. Solar Controller, 30A. Converter, 55A
Connecting the battery - via 2awg to a 500A shunt to feed a Trimetric Battery Monitor
Battery + via 2awg to a Main fuse.
Main fuse to 3 way power distribution block.
Fuse for inverter leg 150A, 4awg
Fuse for converter leg 60A, 8awg
Fuse for solar controller leg 40A. 8awg
Question, what size should the Main fuse be? do I even need a Main fuse?

Hi Bob & Deb,

Fuses are always sized to protect the wire... and sometimes the power source.

- Yes, you need a main fuse! Between the battery and distribution block! For the 2ga wire use a fuse that is rated 200A or less, preferably more like 175A (note that 2ga wire has an ampacity of ~210A). Mount this fuse as close as possible to the battery + terminal, and absolutely no more than 18" away. I chose to mount mine directly to my batteries (see photo below).

- The shunt for your trimetric will be installed in the negative wire and as such it does not need to have a dedicated fuse.

- 4ga wire is too small for your 1500W inverter (IMO, so is 2ga)! Have you considered a dedicated run from the battery to the inverter? Anyway, since you stated that you are using 2ga from the battery to the distro' block then I suggest you use 2ga to the inverter as well. Keep these wires (both + & -) as short as possible. Personally I would select a fuse for the inverter with a lower rating than the one at the battery so that if my inverter caused a fuse to blow it wouldn't affect my other circuits. IF you use the 4ga wire then the fuse must be rated less than 160A.

- For the 8ga wire to the converter, use a fuse rated at 70A or less. Note that IMO 8ga is small for a 55A converter.

- For the 8ga to the solar controller , use a fuse rated at 70A or less.

Hope this helps,
-Mark