Wire sizing/derating

[LarryFine]

I’m realizing I’m not sure conceptually how current flows from phase to phase. I understand that it does, and that that is why no neutral is needed on 240 circuits. But I don’t know why.

It's because 120/240v 1ph is merely two 120v sources wired in series, just like two batteries, which must be wired in the correct polarity for the voltages to add, and not cancel.

When the POCO wires three 120/240v transformers for 240-Delta 3ph, they internally wire each unit's two 120v secondaries in series to obtain 240v from each one.

When they wire them for 208-Wye/120v 3ph, they internally wire each unit's two 120v secondaries in parallel to maintain the full capacity of each of the transformers.

 

[Carultch]

I guess on an atomic level why not have electrons moving opposing ways? My brains thinks they’ll run into each other though.

Electrons are always moving in opposite directions. In fact, their chaotic thermal motion is far faster than their electrical motion, for room temperature circuits. When current is zero, the thermal motion adds up to zero. When current isn't zero, enough of them in the aggregate, cause a net drift of the average electron to carry the current. It's really the opposite direction we consider current to flow, because we assign the electron as negative for historical reasons.

The only current you can ever measure in a wire, is the net current, even if different electrons move in opposite directions at the same time. Everything we know about current in our electrical formulas, is based on the aggregate behavior of billions of electrons (or rather, charges in general), rather than any individual electron.

 

[Pinnie]

It's really the opposite direction we consider current to flow, because we assign the electron as negative for historical reasons.

isnt that the electron theory? I’m reading Mike’s theory book. I know that’s true of dc but I didn’t think that applied to ac too

The only current you can ever measure in a wire, is the net current, even if different electrons move in opposite directions at the same time. Everything we know about current in our electrical formulas, is based on the aggregate behavior of billions of electrons (or rather, charges in general), rather than any individual electron.

That makes sense.

In my understanding, in a typical generator the movement of electrons is generated by the movement of the magnetic field relative to the coils (indicated by someone’s beautifully reposted animated graphic.) I also understand the electrons themselves generate a magnetic field perpendicular to the conductor (I think) when they are in motion (maybe not motion dependent not sure).

do the electrons bump into each other when moving opposing directions?

Do their magnetic fields conflict when in the same conductor?
( I think the answer will be no their magnetic fields combine)

Do all the electrons on a single phase conductor (call it B phase) oscillate in sync at 60hz or are they moving in different directions?