I was asked today about the requirements for powering a 1500W 120V livestock water tank de-icer that was 500-600ft away from the panel. First thought that came to mind was "sub-panel". At that distance is it even reasonable to run conductors straight to the heater? At 500' and using a 3% voltage drop I ended up with #4 Cu (75 degree Celcius column Table 2 CEC). Wouldn't a small sub-panel placed closer to the tank and then running smaller gauge conductors to the heater be a better idea?

Potseal:

Vd for the load in the subpanel would be equal to what you calc'd for just the load.

IF you ran 3 wire & grd to the sub, you would have available 'load' capacity at the area.

Depending on available voltages at a source, 480 volt to the location, and a small 480-120 transformer may be economical.

Potseal, you are under a misconception.

What limits voltage drop issues to branch conductors alone? Circuit or panel - you need to allow for voltage drop. Only a higher voltage will lessen your voltage drop.

Set the 'percentage rule' aside for the moment. What's your final voltage when the heater is in use? If your incoming voltage is on the high side (127V is not all that rare), then you could very easily have a very acceptable 118V at the heater.

Whether you should set a panel is another question. I'm biased in favor, for two reasons.
First, I like having an OCPD, GFCI, and disconnecting means close to the point of use.
Second, you almost always have a later desire to add a light, a service receptacle, whatever in the same area. Might as well pull a 4th wire and have a second circuit.

Run big pipe - pipe is cheap - and you can pull bigger wire later if you need it.

Finally ...don't have 480? Make it. Just use two transformers: one 'up' and one 'down.'

Thank-you for the suggestions. I will definitely consider them as it could solve the distance issue.

FYI

After doing my own calculations I decided to look online to see if I could compare my results to other available information. Found this related chart as a result: