Rob Claus gives us a helpful tip for identifying the service phase of a building.
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I would be careful and not recommend making assumptions or determinations of an electrical phase by simply looking at the # of service entrance conductors (wires above) or even making a determination on voltage.
For us, we utilize several pieces of the puzzle such as utility transformer type, number of wires, metering devices, labeling at panels, color coating of wires, contacting the electric utility service provider, etc. Sometimes we use voltage meters to help determine actual voltage, however I would not recommend this method for a novice. Also, imo, it’s ok if you cannot make a definitive determination of a phase or voltages. You can use several methods in your reporting of stating what you simply seen or even what was conveyed if you site your sources.
And perhaps George W. or Robert M. (experts that frequent here) can provide further helpful information.
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One 3 wire connection is a 3-phase 3-wire Delta System. It uses a 3-phase configuration, not single-phase.
A 3-phase 3-wire Delta System is fairly common. We see it more than you would think. I’ve seen it in at least 8 states. It may be utilized across the entire United States. I’m not sure about Canada or other countries. I’m not going to get into all the technical configurations or voltages of 3-Phase Delta systems, but it can get fairly complex. Voltages range from 480v, 240v, 208v, 120v. And to determine or confirming what the exact voltages are present at each panel would require taking panel covers off and using a voltmeter. If you use a check box type report for commercial (I don’t recommend that style) and you tick or check off a single phase or 3-phase or 120/240v, etc. things can go south pretty quickly. About 6 weeks ago I did a small commercial in NC. The client sent me an old report that was completed by an inspector for the current owner when they purchased it about 6 years ago. This property has a 3-phase 120/208v service. That inspector using a check box style report indicating it was a single phase 120/240v system.
Switching topics slightly. About 4 weeks ago we were in northern KY. One of the 3 buildings had an electrical service I hadn’t seen and what interesting. It was a single phase 120/208v configuration derived from a 3-phase utility transformer using two of the three phases. One of the client’s happened to be a utility lineman for over 40 years. I asked him why it was configured this way, and he stated it’s just the way the utility company did it. He said the city’s electrical grid is older and apparently not reliable. He said they often blow transformers during storms.
3 wires at a service drop does not automatically equal a single phase 120/240v system. I hope this information will be helpful.
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