They can size the 120/240 center tapped transformer to what your expected load is. Typically it is a 37 or 50 in the installations I see and they put in something smaller for the 3p loads.
Where we got in trouble was some of the DP equipment had 3P line cords but contained a significant amount of single phase load. Tape controllers were the worst because the satellite drives could be plugged into any one of 8 receptacles in the controller. As long as you plugged them in in sequence or had a "full boat" they were fairly well balanced but if someone only had a couple drives and they weren't careful to balance them you could corrupt the red leg balance.
I still want to avoid three phase power at home. So I guess the thing to do is make sure I don't build a mega mansion. OTOH, if I were that rich, I could afford to bring in 480/277 and waste power transforming it to whatever I wanted
Actually, If I had that kind of money, I'd more likely be doing something off-grid, anyway.
That is why delta is the best choice. You can run your big loads 240/3p and your 120/240 panel stays the same.
Be careful with your words, not all deltas are centered tapped. I was at a facility, in October, that had both a 240V delta grounded B-phase 3PH 3W and a 120/240 1Ph 3W services.
I assumed we were talking center tapped delta. There are also times I could make a case for corner delta. If your equipment is good for 208, then wye makes sense but you can have harmonic problems on the L/N loads. All of these have good points and bad points depending on your customer. That's why the PoCo still sells them all.
My understanding is that 240 delta with one side center tapped for 120/240 had a limitation that the single phase loads could be no more than 5% to 10% of the total transformer capacity. It's certainly not a choice for buildings that have all or nearly all single phase loads, but so much load that the PoCo puts them in the "must use 3 phase" category.
The 5% loading restriction only exists on center-tapped delta transformers that share a common core. In recent years several manufacturers have starting building some center-tapped single phase units that do not have this 5% restriction.
Transformer banks created by using multiple single phase units may be sized to handle any mix of 3-phase and 1-phase loads.
![[Linked Image from gfretwell.com]](http://gfretwell.com/electrical/red%20leg%20transformers.jpg)
