Boost transformer is one way to deal with it. Can also get ~25% larger unit to get similar output, or in some cases you can get actual 208 volt rated units. Cove heaters is one type that is commonly available in 208 and 240 volt units @ same wattages, as well as 120 and 277 volts.
1/(1 - 25%) = 133%, so you'd want a 240V unit with a rating ~33% bigger than the desired result on 208V.
Technically, a given heat output range wired with 208V instead of 240V elements would have a higher amperage at 208V than the 240V unit would at 240V. The code load calculations all deal with nominal power. The conversion to load amps will be different between a 208V and a 240V environment.
Wouldn't it depend on the kW rating combined with allowed demand factors?
I put in a 1200 amp single phase service to a rural store many years ago, the owner was too cheap to put in three phase even though it was available, so the poco did as you said, they moved all houses to the other two lines.
Quite a bit, used six switch rule, poco transformer was quite a ways from the service, and small. AFC was under 22 k. They wanted to run two sets of 4/0, met with the engineer, and convinced him to run three sets of 350. Another reason the owner wanted single phase was the poco charged residential rate instead of commercial per KW. Way cheaper!
My guess is actual demand was well under 1200 amps as well or else you may not gotten a large enough single phase transformer all that easily by POCO.
Previous 400 amp service was pulling 390 amps per leg at peak times. They doubled the size of the building. The owner was buddies with the poco engineers. They bought all their hunting supplies there.
Depends on POCO. Almost never see that around here. Even open delta systems seldom see with any significant load. On newer services they want to put it across all three phases, though there are some existing older installs that today they wouldn't let customer get new service set up that way.
I can tell you why I design them with 208/120 3 phase and that is because I need 3 phase for the elevator house power. So I use a meter center with the tenant stacks on the right and a house power stack on the left. Also many units now require a 100% outside air unit and that it typically 3 phase power. Once I need three phase I find it best to send 120/208 single phase to the tenant space too.
