1). Why are you referring to the commercial power source as a split phase?
Because that is what residential 120V/240V service is commonly referred to as by many, myself included. Call it whatever you like.
Rustrp said:
2). If this is a feeder then it would be supplying a sub-panel in the outbuilding, protected at the main circuit breaker panel with a circuit breaker of fused disconnect box.
Correct, and code requires that for any more than a single circuit run to an outbuilding. You can't run 2 circuits to an outbuilding without putting in a feeder, panel, and ground rod. It is the only way to do it legally.
Rustrp said:
3). Voltage drop is a factor but a very small one.
Agreed, I wasn't the one raising voltage drop as a concern.
Rustrp said:
4). As a feeder the conductors would be three of the same size.
Most likely yes, although depending on the install the neutral could be smaller than the line conductors as long as it is properly calculated and meets requirements. In some cases, the neutral actually has to be bigger.
Rustrp said:
5). If this was a branch circuit (240 v) you would only have to hot legs and both the same size, plus the ground.
Correct again, but I think you misunderstood my post. I was saying of 100A on leg A and 20A on leg B then I need to size the feeder for 100A, meaning I would use #3 assuming conductors in pipe. If I rebalance the load by moving single pole breakers to swing 40A of load from leg A to leg B, then I would have 60A for each leg and now I would only have needed a 6AWG feeder. These problems tend to happen a lot more in commercial settings than residential. Again, as I said, things generally balance themselves.
I have run into 120V inverter based solar systems were balancing can be a problem, but that is an edge case nowadays.
In commercial settings with UPSs, balancing the 120V loads is critical. I actually had to do that in January. A UPS was slipping into soft bypass because it was overloaded all because one of the 2 legs was much hotter than the other. I moved some of the loads to the other leg, and the UPS went from over 100% utilization (where it goes into bypass) down to the low 90's.
It may not mean much to some, but this allows my company to defer the UPS upgrade to next year.
Rustrp said:
6). How can you provide a 240 v feeder with two differnet size conductors?
Who suggested that and how did you read that into my post? That said, see comment above about neutral. However, my previous post was not advocating using 2 different size conductors for the feeder. Just that if my example 100A/20A load had been properly calculated at the start, and balanced effectively, then the feeder could have been installed as a 6AWG feeder to begin with. Balancing the load properly most efficiently uses both line feeder conductors.
At this point I am done at this discussion. I feel that you are intentionally trying to twist my words and interpret what I am saying differently to try to make me out to look like an idiot. For what reason I do not know, but I am done with it. This forum isn't about that.