wrote:

The neutral carries the difference between the hot leg currents. If the load current is 100A on one leg and 0A on the other the neutral will carry 100A. Increasing the load on the other leg decreases the current in the neutral, so with 100A through both hot legs the neutral carries 0A, not 200A, and it can be the same size cable as the two hots.

Conceptually you get the right answer if you treat both loops of the circuit as separate and then add the currents, If the neutral has 100A flowing in from one hot leg and simultaneously 100A out to the other they will sum to 0

The relevant circuit analysis principle is that the currents into and out of a wire junction have to sum to zero, since you can't create or destroy electrons. A capacitor at the junction doesn't negate this rule, it turns the solution into a problem in differential calculus whose answer is an equation of voltage versus time.

The Romans used the same net-sum principle to run an empire-wide checking system. When a merchant wrote a check for a cargo of wheat in Egypt the amount was simply deducted from tax payments sent back to Rome, and when he returned home the merchant had to reimburse the treasury (or become lion poop). Thus only the heavily guarded tax shipments were at risk from storms or pirates. -jsw

The neutral carries the difference between the hot leg currents. If the load current is 100A on one leg and 0A on the other the neutral will carry 100A. Increasing the load on the other leg decreases the current in the neutral, so with 100A through both hot legs the neutral carries 0A, not 200A, and it can be the same size cable as the two hots.

Conceptually you get the right answer if you treat both loops of the circuit as separate and then add the currents, If the neutral has 100A flowing in from one hot leg and simultaneously 100A out to the other they will sum to 0

The relevant circuit analysis principle is that the currents into and out of a wire junction have to sum to zero, since you can't create or destroy electrons. A capacitor at the junction doesn't negate this rule, it turns the solution into a problem in differential calculus whose answer is an equation of voltage versus time.

The Romans used the same net-sum principle to run an empire-wide checking system. When a merchant wrote a check for a cargo of wheat in Egypt the amount was simply deducted from tax payments sent back to Rome, and when he returned home the merchant had to reimburse the treasury (or become lion poop). Thus only the heavily guarded tax shipments were at risk from storms or pirates. -jsw