Water and electric to 5th wheel

[aczlan]

The difference between -120 volts and +120 volts is 240 volts. The black line represents one leg of a 480 volt supply.

Correct. 240 volts is only measured from L1 to L2 (Red to Blue in the diagram). The black line would be how it is set up in Europe where there are 240 volts between neutral and L1 (or neutral and L2) and 480 volts between L1 and L2.

Aaron Z

 

[Groo]

If you hooked up an oscilloscope to one hot and neutral, you'd get the red or blue lines. If you hooked it up to two hots, you'd get the black line.

 

[aczlan]

If you hooked up an oscilloscope to one hot and neutral, you'd get the red or blue lines.

Correct.

If you hooked it up to two hots, you'd get the black line.

No, you would not (at least not in the US). The Red and Blue lines trace the voltages of L1 and L2 in relation to Neutral (aka, the center "flat line" at the middle of the Red and Blue lines).
If you could read it fast enough, either the Red or Blue lines would go from +120v to -120v (in relation to Neutral) 60 times per second (in the US). The Red and Blue lines are always opposite each other, so when Red is at +120v, Blue is at -120v and visa versa. Thus when you read between Red at +120v and Blue at -120v, you get 240v.

The black line would be Europe where they use 240v like we use 120v.

Aaron Z