Thanks for the clarification 
@bgromicko1 and @gwells
the proper term, and one that helps bring understanding, is “split phase”. The neutral is right in the middle, splitting the single phase.
This also explains why the neutral line in a MWBC is not double the size.
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Split-phase isn’t a bad description for the reason that Bryce mentioned but it is more of a slang term than an actual system designation. The proper term is single-phase three-wire (or 3-wire) system which right there in Bryce’s link. Split-phase does not appear anywhere in the NEC as a system designation.
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Split-phase is not slang. When I thought NEC classes at BGSU in Ohio, I warned the electricians about putting too much stock in the NEC. I had a stack of books in the shape of a pyramid that I would have on a table at the front of the classroom. There were around a hundred books in the stack. Among them were the entire IEEE Color Book Series. Every one of those books help in some way to define the industry. I’d place the NEC on the top of the pile because it is barely the tip of the iceberg.
The NEC is not the sole definitive authority for the electrical industry. If any could be considered to be the ultimate authority, it would be the IEEE. According to the IEEE, “Split-phase” is a term used in electrical engineering to describe a type of single-phase electric power distribution.” It doesn’t get much more authoritative than that!
The American Electricians Handbook uses the term “split phase” to refer to a type of single-phase power supply that is common in North America. [For example, in Chapter 9, Section 9.2, it states: “The most common residential and small commercial service in the United States is single split-phase, 240 V, which features a neutral and two hot legs, 240 V to each other, and 120 V each to the neutral.”
The “Electrical Course for Apprentices and Journeymen” by Roland Palmquist refers to “Split-phase” and “Phase-splitting”.
Merriam-Webster unabridged dictionary has a definition for “Split-phase”.
The American Electrical Engineers Handbook defines split-phase as "a type of single-phase electric power distribution that is common in North America. It involves utilizing two live wires and a neutral wire, each carrying a different voltage.”
I could go on. Split-Phase is a well established, universally recognized electrical term. There are thousands of facts in the IEEE publications alone that are not addressed in any way in the NEC. Also, almost anyone can sit on an NEC committee. It’s obvious from reading the NEC that many of them struggle with basic grammar and sentence structure (including an often referenced 2008 change that experts in English do not interpret the way it is usually interpreted in the trades). The IEEE, by comparison, publishes standards that are developed by some of the best and brightest, certainly highly educated, engineers and practitioners in the entire electrical world.
As I have been telling my students for years, trying to learn the electrical trade, or any other trade, by studying codes is like trying to learn to drive by studying guardrails. Because, that’s all building codes really are - guardrails.
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Awesome article, thank you for all you do for the property inspection industry.
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