Using an Oscilloscope to Understand 120 VAC Split phase Household Power Supplies

Can you believe there are techs out there who use an o-scope to look at the output from a sound mixer and conclude this is how Line voltage works? The output of a sound mixer is the output of a summing amplifier (Google it). It is an electronically modified signal. To look at this output and assume that Line voltage behaves this way is the height of stupidity. I call it "Idiot with an O-scope syndrome."

Household power supplies in North America use what's called a split-phase system. The transformer on the pole outside the house takes grid power and steps it down to 240 VAC from end to end on the secondary winding. The secondary winding has a center-tap in it which splits this 240 VAC into two 120 VAC voltages from either end to the center tap. This center tap is defined as Neutral and it is tied to Ground in the circuit breaker box inside the home. The two 120 VAC voltages are 180 degrees out of phase with each other and it is this very antiphase relationship that creates the voltage difference of 240 vac between L1 and L2. 

There's a lot of disinformation and tech myths out there about 120/240 split-phase household power supplies. You may have even seen videos online claiming that the split phases are in-phase with each other. This is complete hogwash and I prove it to you in this video. 

I show the proper phase relationship (180 degrees) between Line 1 to Neutral and Line 2 to Neutral right at the circuit breaker box using an oscilloscope.


Learn electricity, circuits, and troubleshooting from a proven master with verifiable credentials at the Master Samurai Tech Academy. http://mastersamuraitech.com