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Single and Three Phase e

Single and Three Phase Electrical Power

What's The Difference?


Richard Acree

How can you tell if a structure has single phase electrical power or three phase? And what is the difference? And what is a phase anyway?

Hint: If its three, its one. And if its four, its 3! See the pic below.

Answer: Look at the electrical masts near the center of the picture. There is a smaller one and a larger one. Look closely at the smaller mast and you see 3 wires entering the mast. This is a single phase system. Three wires, single phase. Now look at the larger mast on the right. Again look closely and you can count 4 wires entering the mast. This is a 3 phase system. Four wires, 3 phases.

Single phase electrical systems use alternating current that is synchronized in cycles that vary in unison. I know, what did he say?? Remember, alternating electrical current cycles to peak power like a sine curve, or an "S" turned sideways. By varying in unison the electrical current has "voids" between peaks. Sine curves generally look like this example below from Google Images:

The peak of each curve is where power can be thought of as a maximum, and the spaces between peaks can be thought of as a void. Keep in mind that a typical system in the US cycles like this 60 times per second, so the amount of time when power is not at a peak is very small.

Conversley, three phased power alternates slightly offset from unison. This offset decreases the "voids" and maintains current at peak levels more consistently. That is why 3 phase power is used for devices that need a more consistent supply of power. This includes large motors, recording devices, and medical appliances. These devices do not tolerate the power voids that come with single phase power. See the image below depicting 3 phase power.

Three phase power is more commonly found at large commercial buildings and single phase power is found at most residential structures. Three phase power may be found at a residence that has a recording studio or specialized computer based application inside the home.

At HABITEC Home and Building Inspections, LLC, offering home and commercial building inspections in Nashville and Middle Tennessee, we take it upon ourselves to describe to our Clients what type of electrical power they have in their home or building. This can be important to the Client to make sure the building will will supply the utilities they need.

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Thank you,

Richard Acree

Comments in this article are the copyrighted intellectual property of Richard Acree, President, HABITEC Home and Building Inspections, LLC, and are intended to educate and otherwise assist home owners, sellers and buyers, building owners, sellers and buyers, realtors, real estate investors, property managers, and lenders in the process of owning, buying or selling homes or commercial buildings. HABITEC is a residential (home) and commercial building inspection company serving Middle Tennessee including Nashville, Brentwood, Franklin, Murfreesboro, Smyrna, Mt. Juliet, Hendersonville, Dickson, Belle Meade, Columbia, Spring Hill and more! In addition to building inspections HABITEC offers Environmental Services for mold assessments, radon testing and water quality analysis. Additional information about HABITEC can be found on our website at, or call 615-376-2753.

Richard Acree is the author of the HABITEC Home and Building Inspections Blog and founder of the ActiveRain Group Tennessee Home and Building Inspectors. All are welcome to join and see more blogs like this one.

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