small system design

OK... You are looking for voltage drop... And depending on the chart/website, it may be one way or round trip length. You have to check to see which is which.

For a 1,200 Watt inverter to draw 100 Amps -- Sounds like a 12 volt battery bank. The actual worst case continuous draw is around:

• 1,200 Watts * 1/0.85 AC inverter eff * 1/10.5 battery cutoff = 134 Amps continuous

I suggest a maximum of 0.5 volt wiring drop for 12 volt inverter wiring (11.5 battery under load, 0.5 volt drop at max power, 1.0 drop at max surge power (~2x max continuous power)--Or 11.5 volts - 1.0 volt drop = 10.5 volt inverter cutoff... Using a simple voltage drop calculator for 6 feet (one way run for this calculator), 134 Amps and 0.5 volt drop. Trying several AWG sizes, find that 4 AWG gives:
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.8152&voltage=11.5&phase=dc&noofconductor=1&distance=6&distanceunit=feet&amperes=134&x=62&y=12
Voltage drop: 0.40
Voltage drop percentage: 3.47%
Voltage at the end: 11.1

Generally, fuses (and circuit breakers) do have a delay (you do not want a "fast acting" fuse in this case--Allow some number of seconds to minutes for surge current to not pop the fuse/breaker)... I like to size the wiring for:

• 134 Amps max continuous * 1.25 NEC continuous derating = 167.5 Amp rated branch circuit/fuse ~ round up to ~170-180 amps (next standard size fuse)

Looking at the NEC wiring table (simplified version):

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

You could be looking at anywhere from 2 AWG to 2/0 AWG (depending insulation, etc.)... 

Or, you can look at marine wiring charts and see that 4 AWG is rated for ~160 Amps maximum:

https://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity

Exposed wiring dissapates heat much better than wiring packed in conduit (or non-metallic conduit)... Your choice. (2 and 2/0 wiring is heavy, expensive, and difficult to route/terminate).

As always, starting with the manual's installation instructions is not a bad idea.

-Bill

Fuses/breakers that you install, are there to protect the wiring (fuses/breakers are not near fast enough to "save" an AC inverter with a "problem".

The input fuses that many AC inverters have... I would guess that they are betting that a far number of buyers just connect heavy cable from the battery bank to the inverter (no fuse/breaker).

When dealing with large power transistors that, if the control electronics fail (which the can), If "both" transistors are on at the same time (H Bridge switching to make the "AC"), it is possible that the inverter would smoke and catch fire (and blow through the case), if there was an internal failure and no external/upstream fuse/breaker.

"How close to the battery bus" for the breaker/fuse--I have seen 6-18 inches or less... The answer is the distance does not matter--What they are trying to do is make an "inspectable" value that can be used for a Pass/Fail by an inspector. What you want to make sure is that the "Upstream" wiring cannot short circuit as fuse is down stream a foot or so. Just make sure that hardware is tight, nothing can short circuit, if there is wiring going through a hole, that there are not sharp edges/grommet to prevent cuts into the wire insulation. They figure if the wiring is minimal length before the fuse, less chance of shorts.

-Bill

Yes... Something to limit the current (energy) in the circuit. The fuses inside the inverter are (in my humble opinion) a belt and suspender precaution. If the installer did not install a breaker/fuse off the battery bus, the internal fuses will limit the chances of an internal inverter failure of ending up as a puddle of molten metal. If the owner installs a breaker near the battery bus, then the fuses in the inverter are a bit on the redundant side.

When you deal with UL/NRTL/NEC/etc., the devics (TV, Washer, etc.) all expect to have branch wiring protection (i.e., 15 amp breaker, etc.). The typical house breakers are rated for 10,000 Amp Interrupt--Which is a utility pole transformer's maximum current rating. The breaker will always safely "open" (no arcing/welding/fires) at 10,000 Amp source current.

Obviously, if you had TV connected to a 10,000 Amp 120/240 VAC transformer--And something went wrong--The TV would be an exploding burning wreck before the pole transformer even got warm.

-Bill

The typical installation would also include a 6 AWG wire from the battery negative bus to the ground rod (or at least tied to the wire going up to the AC inverter).

The output of the AC inverter (PSW assumed) is probably floating (the Neutral could be tied to the AC inverter chassis--You have to check manual or the inverter itself).

What happens with the 120 VAC inverter output (floating or ground bonded neutral and/or GFI outlet--at least near "water"/outside) for your level of safety.

-Bill

The 2 socket outlet has one GFI circuit... If there is a fault, both outlets are turned off...

My only suggestion is if you have interior lighting, run that without GFI, or on a second GFI outlet. I suggest that you don't want to be plunged into darkness if the outside (one and only) GFI circuit is tripped, and turning of the lights inside.

-Bill