Not quite, or maybe I don't understand what you're saying. 208 three phase will always be a wye connected secondary with 120v phase to ground. If the voltages are the difference of 1.73 (√3) they are always wye connected. 240/120 is always delta connected as it is 1/2 ratio. phase to phase is 240 and phase to ground is 120, it's a 4 wire system. Phase angles are 120° apart in all instances. RMS has nothing to do with 208v systems.
Agree, this is found in a wye connected secondary.Well, I have to get sort of technical here, so ask questions if this gets really confusing. 208 3 phase is 3 legs of 120 volts to neutral that are 120 degrees apart.
It is one 240V leg center tap split . There is no phase shift just opposite polarities. Same reason why it is not called two phase.Split phase or standard residential wiring is 2 legs of 120 that are 180 degrees apart.
√240²-120²=208 We don't even use the 208v on a delta secondary, do we? 208 is derived from one leg (240v) and the center tap (120v).The reason that its not 240 3 phase is the phase angle difference. the 120 volts is the maximum plus and minus voltage that is referenced to neutral. Now becasue the 240 is 180 degrees out of phase as one leg hits the peak positive voltage, the other leg is reaching it's maximum negative voltage. The difference between the two legs at that point is 240 volts. Because 3 phase is 120 and not 180 degrees apart, only one leg at a time reaches it's max voltage. The 208 is the difference between the two legs at the point of maximum voltage of only one leg and a reduced voltage of the other leg because it's not at its maximum voltage at that same time.
The whole RMS vs Peak is another discussion.
The motor wouldn't start. Each winding would be connected directly across 120VAC and and neither would be subjected to any phase shift. The capacitor would draw lots of current but it would not affect the motor.I'm wondering, (and I should know this) if, in the case of a motor wired for 220 volt, the connection point of the two run windings could be tied to neutral to stabilise the voltage that appears there and reduce the voltage spike/swing impressed on the start cap. The start winding, cap and centrifugal switch are usually across one of the run windings, and I bet the midpoint of the run windings thrashes around quite a bit when starting and stopping. Anybody?
Mark S.
That's actually the exact reason AC became the standard! You see Edison did many demonstrations showing how dangerous AC current was in comparison to DC. He maintained that it would be the perfect thing for executions for example. Well the short version is that the government tried it out, and agreed it was good for the electric chair. Now the government needs to buy AC generators, and the rest is history. That's just from memory but you can find the info if you're interested.Well, to further complicate matters I have heard US power referred to as Edison 2 phase.
Now that makes little to no sense since Edison HATED AC and wanted DC in everyone's house with a small generator in a barn out back.