The circuit breakers described in that article are not permitted for branch circuit protection. In fact, if you look at the catalogs published by Cutler-Hammer, SquareD, Siemens, etc., they avoid "circuit breaker" when talking about these devices and refer to them as "supplementary protectors," and reserve the term "circuit breaker" for devices that can be used as branch circuit protection.
The 90A number for #10 wire that's been bandied about is incorrect, at least for the more common insulation classes. There's an additional provision in the NEC section on welders that says that the overcurrent device must be set to no more than twice the conductor rating, so 70A(for 75C insulation - romex) or 80A(for 90C - THHN) is a more realistic high end.
It is preposterous to say that the electrons flow out and go somewhere mysterious and never return during normal operation. There is definitely a return on a 240V circuit going to a welder. Electrons flow down one leg, thought the transformer winding in the welder, then back up the other leg. Re-examining the situation 16.6mS later, of course the current is flowing the opposite direction. But whatever electrons flow out on one leg of the circuit come back up the other side. Thats why its called a "circuit".
I'm not sure what point you are shooting for here, and you are correct in many cases, i.e. saying that there is no current flow to earth ground. But you are mistaken in saying there is no return. A conductor can provide a return path without being at earth ground potential. Similarly on 120V circuits, the return path is the neutral line, which is also not necessarily at earth ground potential (indeed, because of the return current flowing across its resistance).
Yeah, folks keep insisting that half of the supply leads are returns, but no one is saying where the power or current is returning to/going.
You present a contradiction, I think, by stating (agreeing) that there is no current path to earth ground in 120V circuits, but then stating that the neutral provides a current return path, although the neutral is actually bonded to the structure's earth ground rod in most instances.
Neutral isn't anything other than a reference point. That reference point is essentially zero since it's bonded to earth ground. That essentially zero point is present at one side of a 120V lamp or appliance cord. It stays at the reference point of essentially zero. One exception to this would be at the precise instant of a very close lightning strike, when the reference changes, and often results in damage. In a 120V lamp circuit, the neutral is lower or higher in potential than the home panel's bus bar (either one), depending upon the amplitude of the zero-crossing sinewave. The 120V lamp doesn't care if the voltage potential is lower or higher, it just lights, dims and lights at 60 cycles per second.
So, for those that insist that the neutral is a return path, they're still not correct in thinking that the neutral is returning current half the time, as a result from being a lower or higher potential (to the bus bar), because it is still just an essentially zero reference point. The only time the lamp lights is when the line (bus bar) potential is not zero.
Where the current goes in a 120V lamp, is into the filament resistance. The neutral is still just an essentially zero reference point. The light and heat are the product of the 120v being dissipated by the filament's resitance, and there is no left over power or current to return to anywhere else.
As I said before, I don't see the point in discussing electrons when considering electrical power applications. The duration of a sinewave is not it's rate of travel, it's the frequency at which the AC alternates. The frequency of the cycles has nothing to do with how long a cycle spends in the load, or how fast it passes out to somewhere else.
In a 240VAC circuit, what about the other phase, then? Is current from L1 returning "out" on L2, then L2's current returning "out" on L1? Fascinating, if you could show that happening, don't you think so? If everyone would limit the "return" current, they would save energy?
What I have said before, is that the two 240VAC input terminals at the welder transformer are basically taking turns being the higher potential, while the difference in potential is 240VAC. The changes in potential (alternating voltage changes) create current in the resistance of the winding, and are dissipated in the transformer's primary winding.
AC can be distributed for long distances with only minimal losses. It doesn't flow in a circular pattern, out one conductor and through a load and back out to the other. It's either present, or it's not.
Any of this real science can be tested/proven by experimenting with a common power transformer. Since many homes are supplied power from a nearly identical source, it would be simple enough to make an equivalent house service panel setup with an isolated center-tapped 24VAC transformer secondary winding (or secondary voltage of choice).
-Holly
For AC, it's not a return path, it is only a different potential. My question remains.. return to where?
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