What gauge Wire to run from Inverter to house breaker?

[Blue Grouse]

This would be a 77' run. The Panel cables that go to combiner box are 12 gauge, then I believe the plan is to go to Inverter with 10 gauge.

Anyway, it's a 77'run then from the Inverter to house breaker. Is there an online calculator to figure our wire gauge?

[solarix]

Need more data... How many amps? How many watts is the Array? What voltage is the combiner output?
Just google voltage drop calculator - there are lots of them, just be aware what you want is minimum efficient size, not minimum safe size.

[Droo71]

.. 12 gauge seems small to go to a combiner box -- I'm going less than 20 to the combiner from my panel strings, and all of my PV wire is 10ga. Then from my combiner box to the power center is 6ga , and its only 35 feet. (45A@ 125ishV) .

My inverter out to the AC panel is 6ga, but only because that's the smallest wire my panel will accept at the lugs, and its only 6 feet apart. NEC/CEC both list 10ga as my minimum spec, 30A per wire. Inverter to battery is 24V/205A max, so 4/0 , 5 feet.

So, how much power are you pushing - and you are feeding the inverter directly off the combiner/integreated MPPT ?? Or are you going to separate charge controller first?

[foo1bar]

So, how much power are you pushing - and you are feeding the inverter directly off the combiner/integreated MPPT ?? Or are you going to separate charge controller first?

Since this is in the grid-tied section of the forum, I'm going to guess that there is no charge controller - its just an inverter. No batteries involved.

Solarix is right - need more information to give a useful answer.

What size inverter is it? What size is the array? Which brand/model of inverter? Is this in the US and a residential installation? (is it 240V? Are you under NEC requirements?)
Those will give the information on how many amps. And based on that can look at 1> voltage drop and 2> minimum wire size requirements per NEC for the breaker being used.

At only 77 feet, probably requirements from NEC table will dictate the wire size. If we're talking a 40A breaker, that'd be 6AWG aluminum per table 310.15(b)(16)
That'd support a 7.6kW inverter running 240V, 32A. voltage drop on that would be much less than 3%.

[Blue Grouse]

Sorry for the delay getting back to you. Again, folks, a GRID TIE project. This would be a 33 panel system, broken down into 4 arrays (3 arrays w/8 panels, 1 array w/9 panels). The specs for each Panel is:

• Power: 400 watts
• Vmp: 40.7VDC
• Voc: 49.58VDC
• Imp: 9.83 A
• Isc: 10.35 A
• Module Efficiency – 20.13% (using STC – standard test conditions)
• MC4 Connector
• Max Series Fuse rating: 20A

The Inverter is a Fronius Primo 11.4-1

Operating Voltage Range: 80 VDC to 600 VDC
MPP Voltage Range(peak efficiency): 240 – 480 VDC
Recommended PV Power: 9,100 – 13,700 watts
Max. Usable Input Current (MPPT 1/MPPT 2): 49.5A/27A
Total Max. DC Current: 51A
Grid Connection: 208 or 240 VAC
Max. Output Power: 11,400W (for 208 or 240 VAC)
Max. Output Current: 54.8 A(208 VAC), 47.5 A(240 VAC)
Ambient Operating Temperature: -40 to 140 degrees F
Fan Cooled

[Mike90250]

That odd 9 panel array, does the inverter have several MPPT inputs ? Otherwise, the 9th panel is a wasted panel. park it in the garage as a spare.
if it only has a single MPPT channel, you will need a Array Combiner Box that will safely parallel your 4 arrays. Over 2 arrays, requires a protection panel to prevent a bad panel from burning from other panels feeding it ( that's the Short Circuit Fuse spec on the back of the panel ) Breakers are better than fuses, as they can switch individual arrays off to compare performance for troubleshooting. Most fuse holders are NOT rated to open a circuit.

All arrays connected in parallel, need to be identical. Some inverters have multiple MPPT inputs, some do not.

As for the wire, from inverter to panel, I'd use 55A as my target, and go one size larger than code. If the inverter and panel are rated for aluminum wire, i would for sure use aluminum wire and save $$


in copper, that would be #4 AGW if using aluminum wire, it would require #2 - if it fits in the terminals. By the time you buy splice adapters to go from copper, to alu and back to copper, all the extra parts may just pay for the copper instead. Price it out both ways.

https://lugsdirect.com/WireCurrentAm...ble-301-16.htm

Or, you may find a wire Ferrule may reduce the gauge of a stranded wire to a size that will fit in the terminal set screw ( going from #2 aluminum to #4 copper )

https://www.ferrulesdirect.com/colle...-wire-ferrules
https://www.americanelectrical.com/c...wire-ferrules/

All have to be rated to handle the aluminum parts.

[foo1bar]

The Inverter is a Fronius Primo 11.4-1
...
Max. Output Current: 54.8 A(208 VAC), 47.5 A(240 VAC)

I'm going to assume 240VAC (typical for residential in US)

So you have 47.5A (continuous)
So: 47.5A * 125% = 59.375A (have to do 125% because it's a continuous current and most breakers are not rated for 100% current for "continuous")
Which means a 60A breaker.
I'm looking at the NEC table, 310.16.
I'm *guessing* that you'll be in the 60A column (unless your connections at both ends are rated for 75 or 90, and so is your wire.

60 degree, aluminum column, says 3AWG would be OK for 65A,
4AWG for 60 degree copper - but properly anti-ox'd and torqued connections on Alum are just as reliable as copper IMO. So knowing the difference in price betweeen Aluminum and copper, I'd go AL.

So now to calculate voltage drop (rise in this case) - make sure that's acceptable.
3AWG Aluminum for 160 feet
48A current.
Calculator I find on the web says 1.3V for those conditions.

So at maximum production, if your voltage at the panel is 240V, the voltage at the inverter would be 241.3V.
That's well under 3%, and IMO that means it is unlikely that you'd run into case where the inverter turns off because the voltage is too high.

I'm not an electrician - and I'm not guaranteeing my calculations were done correctly.
But the above should allow you to do your own calculations and give you things to research to reach your own conclusions.

Good luck.