On Thursday, January 4, 2018 at 3:23:33 PM UTC-5, Mr. Luddite wrote:

Many people assume it is the sum of both current draws or 70 amps in
this example and it's amazing how many "electricians" don't know that.
They don't realize that the two "hot" legs are 180 degrees out of phase,
so the current in the neutral adds algebraically.

That's why the neutral feed from the street to your power panel is the
same size wire as the two hot leads. It will never carry more than what
one hot leg is rated to draw.

That reminds me... I've had the "discussion" with more than one intelligent person about a car (or insert motorized vehicle here) battery and it's role in running the car. Had more than one person assert that, once started (cranked), the battery runs the car and the alternator charges the battery.

Of course, that's just not the case. The alternator runs the car's systems (lights, ignition, etc...) while it recharges the battery for the next cranking cycle. It's not as if the electrons are smart and go to the battery first, then back out to the car! For the charging to occur, the alternator's output potential (voltage) is higher than the battery's, so it supplies the current to the car's systems and the leftover goes to the battery. Once charged it reduces its output voltage, and if it goes below the battery's voltage the battery would take over, but then become discharged and the alternator would ramp up and take back over. That shouldn't happen in a properly designed system, it should just go to float mode which is just slightly higher than the battery.