Long electrical power run

I'm oversimplifying the project, but assume I want to power an outdoor 120V LED floodlight that needs 50 watts of power, that is located 1400' from my load center. That's less than 1 amp at the light.

The Southwire voltage drop calculator says I need to run 10 awg wire to keep the voltage drop below 3% at 1 amp.

Now assume a future property owner (that knows even less than I do) adds additional equipment (but nothing with motors, etc.) at the same drop location that increases the power draw to 6 amps total when everything is powered up. The voltage drop calculator says 6 amps at the end of 10 awg wire 1400' long will cause a drop of about 17 volts. Also assume that the future owner doesn't do anything to compensate for the additional draw, e.g., adding a boost transformer, re-pulling a bigger wire, etc. He just wires the new stuff in.

What happens when everything powers up? Does it throw the breaker back at the load center? Does it melt wires? Does it damage the equipment? Does it depend on how the floodlight and equipment handle 103V instead of 120V?

Incorrect wiring size will cause additional heat (and may cause shorts/fire hazard). I recommend the following link for some information:

Anything is feasible; however, safety is a primary constraint. I would recommend that a qualified electrician design your circuit (including a dedicated circuit breaker, wiring / wiring installation definition, and any thing else required to make a safe and reliable installation.

As far as behavior of added equipment later on: if the equipment usage dos not exceed the circuit design, it should be no issue. If it does exceed, the breaker should pop. Most equipment in the US will handle down to 100V. (The bad news is that the US standard for the supply is 110 to 120 V, so if your municipal supply is at 110 V, then you are talking about 93 volts. )

There are other options to consider for a remote system:

  1. Separate power drop from your utility, if you plan on more usage.
  2. Small off-grid solar power system (Amazon search term)
  3. Solar - wind powered off-grid combo.
  4. Solar Street Light (Amazon term)

Depending on your load center panel, you may be able to get a 2A breaker and design for that maximum. Then I would also put a label at the end outlet identifying it as a 2A max load.

As far as heat build up, the heat is going to be distributed across the length of the run. Heat would only be a concern if you were coiling the wire up and putting it in a box.

Even at 6a, I wouldn’t expect a 15A breaker to trip. And, TBH, I wouldn’t expect the wire to heat up to dangerous levels. Whatever load is on it may not like that voltage drop. In the US, 110-127 is considered a safe range.
That said, if you were closer to 75-80% of the breaker/wire rating, I would be concerned about wire and more specifically terminations heating up, and possible breaker trips.
Last summer I had my camper plugged into a 100 ft 12AWG extension cord fed from a 20A breaker… just to run the AC and the fridge - about 14-15A of load with both running. I started having random breaker trips. Then I noticed burning/melting at the connection points between camper cord and extension cord and the camper inlet and camper cord. I ended up having to replace the inlet and cord.
I have since made up a 130’ 8AWG cord (expensive!!!) with a 20A plug on one end and a 30A travel trailer plug on the other to plug directly into the camper. I also tasmotized an S31 to leave in there - with custom rules and driver to report voltage changes over 0.15V and any excessive voltage drop. In my case, I use 6.7% drop as a notification threshold when compared to the most recent good voltage - when the AC is not running… since “good” voltage fluctuates dramatically - especially hot summer days. It’s not uncommon that my “good” voltage at the camper is 124V first thing in the AM and 118V mid afternoon.

Have you considered running 240VAC and installing a step down transformer at the far end ?

I did a system at work where I had to get power distributed over multiple acres of area. By doing a 480V 3 phase distribution with transformers, we were able to run much smaller feed wire.

In my case, that was too much work - a larger gauge cord worked for me. But yes, you can run smaller wire at higher voltages as an option and then step it down.
For the OP, if I was really concerned about it, I’d add a fused disconnect fused very low.

A bit off topic since this was not the question...

Have you considered a solar powered flood light, my old neighbor has one he got from Costco for like $50 or something near and this thing was crazy bright. I think he could make if dimmer for always on and then brightens up when movement is detected.

Running 10 GA wire 1400' long and all the headaches around "what if questions" is just not worth it considering solar light offerings in 2024. Even in shaded areas, solar panels can charge up enough to keep light on all night long.

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Post deleted by OP.

Thanks for the comments.