Source, Battery, Charge Controller, Panels, etc.
Fuse/breaker as close as practical to Source.
Wire/Cable that will conduct MAXIMUM load (inverter/lights/whatever)
Oversized circuit protection, or undersize wire/cable is dangerous.
Undersized cables will 'Starve' the load and heat up,
With an Oversize fuse/breaker the wire/cable can get VERY hot and the protection won't activate.
Fuses/Breakers are used in TWO different ways,
1. To protect wires/cables when they fail. (Damage, corrosion, etc.)
2. To protect a specific appliance from excessive load draw.
The fuse/breaker heats up first and blows/trips BEFORE the cable heats up and melts insulation, start fires on the wires/cables, and are *Usually* sized a little big, or 'Slow Blowing' to allow momentary over demands to pass without blowing/tripping.
The device protection (fuse/breaker) is sized MUCH closer to the operational load the device is *Supposed* to demand.
There is a reason so many devices come with their own circuit protection that can occasionally burn/trip, and the reason is they are sized specifically to protect the device and not protect the main line.
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SO!
Now you have a battery/batteries of 1,000 amps,
Now you have cables capable of 200 amp supply to inverter,
Now you have circuit protection, say a fuse at the battery to cable connection that will melt at 220 amps if the cables are dead short circuited together...
You have a sharp edge rub through the insulation and contact something that's chassis 'Grounded',
Something like sheet metal that only takes 30 amps to melt into molten slag, orange hot pools of liquid metal...
TWO things are going to happen fairly quickly,
The first is the 220 Amp fuse IS NOT going to burn and disconnect the batteries from the cable.
The 30 amps required to melt thin steel into puddles is not going to trip a 220 Amp protection device.
60 amps will melt/weld 2 pieces of 1/4" steel AND the welding rod, and still not trip the circuit protection.
The 'Smart' money is spent on insulation & armor for the battery cables ANYWHERE they touch anything that can damage insulation.
The second thing that's going to happen is you will have orange/yellow hot ball of molten metal dropping on anything under them.
Hopefully you have a $15 smoke detector stuck right above your primary wiring!
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Watts ÷ Amps = Volts
Watts ÷ Volts = Amps
Amps x Volts = Watts
Volts x Amps = Watts
This is a constant.
The
LOAD determines how many Amps gets dragged through any given wire/cable/terminals/connection points.
1,000 Watt Load, powered by a 12 volt battery/batteries in parallel,
1,000 Watts ÷ 12 Volts = 83.33 (84) Amps.
Discounting any resistance from terminal ends, stacking terminals, etc
That's a 4 Ga. Wire size minimum to conduct that 84 Amps,
4 Ga wire will conduct 92.3 Amps
(Always round UP and size UP)
I use the Brown & Sharpe scale, once I find amperage, I simply look up the amp load (rounded up) and then see what wire gauge size handles the amperage.
This is the scale the American Wire Gauge is based on, adopted almost directly.
Find your amperage in the 'Amps' column, follow far left for wire size.
View attachment 2327
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Everyone will do what's best for them...
I personally won't mount something with high amperage directly on anything flammable.
While plywood is an electrical insulator, the glue & wood are flammable.
A small piece of sheet metal from the hardware store behind the inverter, charge controller, etc is a heat shield/fire retardant.
For the DIY types that scrounge, stoves, fridge/freezers, washers/dryers, anything made of sheet metal that's handy will donate.
Another source is stove pipe that snaps together (steel or aluminum).
I keep anything flammable to a minimum in my unattended solar/machine room.
I've seen big truck battery cables melt through the heat treated frame, battery cables melt through angle iron battery racks, etc.
Nothing to catch fire, so the things I saw didn't burn completely down, or they would have been in the junk yard instead of being repaired, but I tried to learn from the experiences...