In my opinion, there ought never be another 240/120 Delta system installed, ever. 208/120 Wye is the only way to go. You just can't beat having a real neutral.
I would agree. I would not want this kind of system. If I need to power 240 delta loads that can't do 208, I'd rather do it with 240Y/139.
Appliances and motors are, by NEMA conventions, intended to operate within 10% of their nameplate voltage. Combine this with the fact that most 208 services actually deliver closer to 212-215 volts, and a 230v rated appliance ought to do just fine.
Based on voltages many people have reported in various postings I've read online, this isn't quite true. There are cases where the actual voltage is slightly lower than 208.
There are other issues that make it necessary for motors to have some operating range. Services often vary in median voltage. Tariffs I have read give the PoCo a 5% leeway in most cases. And that's on the median voltage. The voltage can also vary hour to hour or day to day. And that's before we have cases like hot summer brownouts (which just end up burning out more air conditioners). 208 is on the very edge of the +/- 10% range centered around 230. That gives none of the leeway for other issues. Most things will try to work on 208. But sometimes they will fail.
This situation is what I had in a business I worked at, once. It was an office pad environment, with each unit having its own A/C system using single phase power. Ours was cooling a substantial computer room (about 60 computers) and one summer it failed. A blower motor had to be replaced. Then it failed again in 3 days requiring the same blower to be replaced. Over the course of 3 weeks, it and another motor were replaced several times. The A/C service company special ordered a couple 208 volt single phase motors and substituted those, and the failures stopped. This was in the peak of summer when the A/C system was forced to run continuous. That and the heat on the roof was killing it. The 240 (230?) volt motors worked on 208, but not well enough to work in the adverse conditions a true 208 volt motor would work in.
There should have been a 208 volt three phase A/C system there.
Yes, heating elements will be affected, and in many cases the appliance maker will have 208v elements available. (I encountered this with a restaurant 'booster' heater, that had been ordered for the wrong voltage).
For commercial and industrial equipment this is common. In fact I found some cases where 240 volt was not an available option (even when 480 was an option).
One blessing of three phase is that motors now require motor starters. I say this, because the new ones have electronic overloads ... and incorporate low voltage protection, phase imbalance protection, etc.
That would certainly make things better, whether three phase or single phase.
As for the panels .... what you do is determined by the service the PoCo gives you.
And it can become a real mess if you have to change it all.
If they give you Delta, the original panel stays - but is fed by a new 'main' panel. You must do this to stay within the listing of (strangely enough) the three-phase panel; the fine print will tell you that UL doesn't want single-pole circuits in a delta-fed panel. I suppose they want to require a smarter idiot in order to mess things up.
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.
Consider the situation where a business has single phase service and lots of equipment that uses 240 volt single phase as the bulk of their load. One example that comes to mind are kilns for ceramics and glass work. They want to expand, but the additional loads requires three phase service. How do you avoid having to replace all the existing 240 volt kilns when they can't be changed in the field?
If the limit on single phase service is, to pick a number, 400 amps, then why not add additional service from another phase, up to 400 amps. If the expansion were a separate building, that would be workable.
BTW, larger single phase kilns typically can be rewired between 240 and 480. The 208 volt ones can be rewired between 208 and 416. Many smaller kilns, however, are single voltage (you specify the voltage when ordering).
I would not want to put boost transformers on all the kilns.
If you're given Wye, then it's panel change-out time. You can't very well have a hot leg pass through the main panel, can you?
The problems are greatest when a change is forced. but there can even be problems for homes forced to use three phase power right from the start, due to lack of 208 volt products.
I'd avoid the 'triple split' arrangement like the plague. Apart from the balancing issues, you have the very real chance of some circuits - especially after a few remodels - having conductors (especially neutrals) divided among several panels.
Are there technical issues with "triple split"? Or is it something that complicates things too much?
If I was wealthy enough to have one of those mega mansions and had to take three phase, I'd just insist on it being delivered as 480Y/277 and go with three 480 to 120/240 transformers.