Why does AC wire size change from 120v or 240v same distance?

[jfharper]

Say you want 55 amps over 100 feet single phase 3% voltage drop, using a calculator, it's 6 AWG for 240v single phase, or 4 AWG for 120v. Is that because the push pull of electrons are occurring on both legs of 240 to help each other, and 120 you only have push pull on one leg (neutral is lazy doing no work)?

 

[timselectric]

Say you want 55 amps over 100 feet single phase 3% voltage drop, using a calculator, it's 6 AWG for 240v single phase, or 4 AWG for 120v. Is that because the push pull of electrons are occurring on both legs of 240 to help each other, and 120 you only have push pull on one leg (neutral is lazy doing no work)?

The "push pull" is the same for both. (60 hz)
The difference is the voltage. Higher voltage travels better.

 

[kayakingphotos]

3% of 120 volts is 3.6 volts
3% of 240 volts is 7.2 volts

The higher the voltage, the greater the voltage drop can be even at the same percentage.

You get an additional benefit if you are trying to move the same wattage.

55 amps at 120 volts is 6,600 watts. Now if you are trying for 6,600 watts at 240 volts, you now are at only 27.5 amps

Now you can use an even smaller wire since you went up in voltage and down in amperage.

 

[jfharper]

So lets say I have an electric stove rated at 10Kw, 240v, that should be 42amps per leg maxed out. If I run two 6 AWG hot wires, and a 6 AWG neutral, at 100 feet, that would cover 55 amps per leg for that stove, with a 40 amp double pole breaker. Now if I wanted to add some 120v on either leg, I would only have 55-42amp available...do I have this correct?

 

[timselectric]

So lets say I have an electric stove rated at 10Kw, 240v, that should be 42amps per leg maxed out. If I run two 6 AWG hot wires, and a 6 AWG neutral, at 100 feet, that would cover 55 amps per leg for that stove, with a 40 amp double pole breaker. Now if I wanted to add some 120v on either leg, I would only have 55-42amp available...do I have this correct?

Basically yes.
But not on a 40a breaker.

 

[jfharper]

Basically yes.
But not on a 40a breaker.

My bad, the range should have #6 and 50 amp breaker at panel nearby, then if I connect that panel to another panel 100 feet away using #6 the far panel should have a 60amp breaker at the #6 connection? Then that far panel is fed by two 6500ex's split phase.

 

[timselectric]

So it's ok to push the breaker a little above what the wire ampacity is rated at for a certain distance (i.e. #6 @ 100ft is 55 amp, but breaker is 60amps)?

You are allowed to round up to the next standard size.
But I wouldn't figure things that close.

 

[timselectric]

Also keep in mind that this is a range. It's going to be a rare occasion for all burners and the oven to be on at the same time. The 120v loads are almost never going to be a problem.