I am trying to illuminate a tunnel about 3000' long temporarily with 9- 400 Watt Metal Halide fixtures spaced about 320' apart. I have a 120/240 generator single phase that I will use to back feed a 240/480 volt transformer to deliver 480 volts, single phase to the tunnel lights. At 480 volts I do not have a lot of load, only about 9 amps, but I am worried about the voltage drop using a romex type nm cable. By using the voltage drop formula I figured that I could use 10-2 romex and a buck / boost transformer every third light. Has anyone had some experience with using romex cable for long, long distances. I would appreciate any input. Thanks

There is some ambiguous info here:

Voltage and amperage of the lights? I can't tell. 480V, 400 W?

Look for a 3% drop and remember to use 6000' . Use currents and voltages within range of the largest current of the ballast and within the operating voltage range.

Wire is wire. Well sort of. I doubt romex will be a problem. I believe it's rated to 600 V.

I do think you should ground the generator to earth and keep the grounds intact to the ballasts which would probably keep the ballasts happy.

Let's see if we come up with the same wire gauge. So what's the max current of the ballast at what operating point? What is the voltage range of the ballast?

If the buck-boost transformers are needed, you might want to size them a little higher in wattage for some of the beginning lights, just to get the characteristic impedance down. I'm assuming that you want to add a few volts on the transmission line.

Does that make sense?

Isn't this FAR outside the scope of a DIY site. I mean the forum heading behind "Electrical & Lighting" is "Home & Garden"

Probably, but the knowledge base of the people here is pretty high.

So, was the guy asking about 3 phase rotary for his garage but he wouldn't answer the questions proposed hence he got no useful response.