Fuses and Wire

[Paratus]

Hello,

New to Solar and this forum. I have been watching the videos and reading what I can, buying left and right... What I am not seeing is a resource on wire size and fuses. I am starting out with a Harbor Freight 45 Watt system and my beginner course using a 12v 35Ah battery, then I have a kit (100x4 Panels, 500w controller and 2 6v batteries, plan on using a 1500w PSW inverter. eventual system will be a 24v, 800w panels, 3000w inverter via 4 to 8 6v batteries.

So I guess my hope for some guidence is the beginner system and the next system on fuses and wire size. I think the general wire is either 8G on the single battery. For the tied batteries 1G between the batteries and 4g to the inverter. It's the fuses I get confused on.

Anyway, thanks in advance.

 

[John Frum]

Wire size is based on the max planned load and/or charge current.
Fuses are based on wire size.
Fuse should be sized between 125% of the planned load and/or charge current and the capacity of the wire.
This calculator https://baymarinesupply.com/bosns_corner_wire_sizes
will help you determine the wire you need for a given load over a given distance at a given voltage.

The ampacity table further down the page will help you determine the capacity of a given wire gauge which will determine the upper limit on fuse size.
The calculator and tables assume pure copper wire with insulation rated to 105C.
With that in mind how hot do you actually want your wire to get?
Personally I don't want my wires to get hotter than the boiling point of water so I also consult this link.

https://www.usawire-cable.com/pdf/nec-ampacities.pdf

 

[Hedges]

Fuses are basted on wire size.

+ = ??

Most of us use those things for watering batteries, if we don't just aim and pour.
Or do you mean that's how you check wire temperature with water, to make sure it is below the boiling point?
I've always licked a finger for that test.

 

[John Frum]

View attachment 22520 + View attachment 22519 = ??

Most of us use those things for watering batteries, if we don't just aim and pour.
Or do you mean that's how you check wire temperature with water, to make sure it is below the boiling point?
I've always licked a finger for that test.

Please don't confuse the newbie.... more than I already did .

 

[Hedges]

Please don't confuse the newbie.... more than I already did .

Fuse should be sized between 125% of the planned load and/or charge current and the capacity of the wire.

OK, so if I'm planning to draw 100A, and I'm going to use 12 awg ...
125% of 100A is 125A.
Ampacity of 12 awg is 30A (from one NEC table)

Should I use a fuse between 30A and 125A?

 

[Hedges]

I should have waited until your hour was up before making fun of your typo

 

[John Frum]

OK, so if I'm planning to draw 100A, and I'm going to use 12 awg ...
125% of 100A is 125A.
Ampacity of 12 awg is 30A (from one NEC table)

Should I use a fuse between 30A and 125A?

No, you should check the ampacity table that I linked to find a wire that exceeds your fuse rating.

 

[Paratus]

Thanks guys. Definately appreciate the input and guidence. Always good to have a little fun while learning!!

 

[Zil]

Blue Sea has an easy to use wire size calculator. If you put 5000 in the upper right box marked "battery cca" it will help find a fuse for LiFePo battery..