Electrician Talk banner

Split Phase

9K views 64 replies 20 participants last post by  lightman 
#1 ·
Okay. Be nice. What is split phase in residential lingo.:laughing:
 
#16 ·
The way we tap it, you are splitting A SINGLE phase of what the power company supplies. If you were to look at leg A and leg B waveforms simultaneously on an oscilloscope, you would find them 180 degrees out of phase.

On a meter, that's why one leg to ground is 120 but leg to leg it is 240. If it were actually ONE SINGLE PHASE twice on two lugs, you would read zero volts from leg A to leg B.

Theoretically you could take leg A from the house to your own experimental 1:1 center tapped transformer. You would take A SINGLE PHASE (leg A) to the primary and you would get 60 from terminal A to center on the transformer secondary, 60 from terminal B to center, and 120 from A to B.
 
#17 ·
Legs A and B aren't different waveforms, they are opposite sides of the same waveform because they are the same phase. That's why they are 180° out: They have to be or else no voltage would exist across the winding.

Putting a center tap in there doesn't change how the coil functions, it just gives you another measurement point.
 
#22 ·
I notice in some areas it seems the residential 120/240 transformer is tapped off of 2 phases, instead of one single phase and ground.Or am I not seeing things right?
 
#32 ·
The wave is most defiantly not 2 phase matt. Read the wiki article on split phase power. Then read allaboutcircuits.com alternating current chapter ten. All you would be doing is refrencing the single waveform at two diffrent points.
Your transformer diagram you drew would have phasors for both readings at 0 degrees. Were the polarity on the left reversed as it would be seen from an o scope you would see one phasor at 0 degrees the other at 180. The circuit has not changed at all but the instrument is telling you something different. Remember we must be smarter than our tools.
 
#42 ·
If you ground your oscilloscope to the neutral and connect channel 1 to one leg and channel 2 to the other leg, the two waveforms on the screen will be 180 degrees apart. That doesn't mean that they are two different phases. That just means you are measuring opposite ends of the same phase relative to the center point.
 
#51 ·
We have some customers that still use it. Entire plants set up 100 years ago as 2 phase, so it's cheaper to keep that distribution than rebuild the plant.
Cue Scott-Tee Transformers.

BTW, on the history, they were set up for Edison's DC scheme.

When everyone realized that Tesla//Westinghouse's scheme was the hands down winner, the original Edison adopters went over to two-phase... and then pitched Scott-Tee transformers.

It was a win-win-win -- as lighting loads didn't need three-phases.

[ They were a tad short on electricians and wire back then, too. ]

{ Once they jumped away from DC, the voltages available exploded upward. That was double-plus good. Edison's scheme was a copper hog. }
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top