View attachment 23678In the schematic above, presume the primary winding on the left is powered by 60 Hz AC.
Measured with respect to gnd, is point A in phase or out of phase with point B?
Take the bottom wire of the winding on the bottom and connect it to the bottom conductor of the top winding and you will have the very same thing our homes have, a single phase center tap system that is in the next post.
What you have is two independent 120 volt systems assuming that the device you have the conductors connected is a NEMA listed device. What you can’t get from this system is 240 volts therefore something very different than what is being discussed.
View attachment 23679ok, here is an image showing the out of phase relationships between the tapped winding. If I remember right, with a tapped secondary, the phasing is different because the start and ending windings are reversed due to the tap. Did I forget something?
I can’t see anything in this image that would lead someone to believe that anything is out of phase, in fact it looks to be in phase.
As labeled the start winding is starting at zero rising to a peak positive while at the same time the other end of the 240 volt winding or finish winding is starting from zero rising to a peak negative. As this voltage passes through the diodes the voltage is ratified to a pulsating DC voltage by letting the negative pass one diode and the other letting the positive pass.
Just like a battery while one end is positive the other is in phase by being negative. This must happen in order to have a difference in potential so current flows. The center tap or neutral point as defined by the NEC “Neutral Point. The common point on a wye-connection in a polyphase system or midpoint on a single-phase, 3-wire system, or midpoint of a single-phase portion of a 3-phase delta system, or a midpoint of a 3-wire, direct-current system.”
It is neutral because while the start winding is positive and the finish winding is negative the neutral is just that, positive and negative at the same time. Should a 120 volt appliance be connected across the start winding while it was positive then the neutral would be negative to its respect. If at the same time an appliance of half the wattage as the start winding be connected across the finish winding While it was in the negative then the neutral would be positive to its respect but half the current of the appliance on the start winding would be across a 240 volt load and the neutral would carry the rest. The only 120 volt current to be found would be half of the start windings load. All of the current on the finish winding and half the current on the start winding would be across 240 volts.
Take two keylesses and connect them in series and to a two pole breaker. Install two 40 watt bulbs and energize. If the two 120 volt breakers that make up a two pole breaker were 180 degrees out of phase with each other something crazy should happen. Want to know what will happen? They come on just like any other 40 watt bulb, yes they do this without a neutral. Use a three conductor cable and use a two head flood with one on one side of the breaker and the other on the other side of the breaker. Flip it on and then remove the neutral and it is easy to see that the two 120 volt circuits are indeed in phase with each other.
Through that damn scope in the trash and spend a little time just thinking and one can see that the windings of a single phase transformer is turned all in the same direction. In most cases the secondary is not even a wire but instead a sheet of metal.
http://www.youtube.com/watch?v=fe4hs30LoGs