What is Three Phase Power?

If you’ve ever been a large scale shop, you’ve seen the size of the equipment they use like a large Planer or an powerful dust collector, and, chances are, the first thing you think when you see a machine that big is “How the heck do they power that thing?!” Well, the answer, while complex in explanation, is rather simple. Large machines usually use three phase power.

What is three phase power?
For those of you unfamiliar with the topic, three phase electricity is a multiple phase, or polyphase electrical system that is favored in large operations due to its robust efficiency. If you’ve ever seen large power transmission lines on the highway, they are all three phase. The basic principle behind it is that there are three circuit conductors of the same voltage and frequency running at a 120 degree offset to each other. Unlike the standard single phase power, this has one conductor. The three phase motors run more efficiently by delivering three times the power in smaller comparable sized conductors.
Can we get that in English, please?
Certainly, observe the graphs below. In the first graph, notice the blue line that is one single phase. That shows the frequency variation in one certain section of generated current. This is the standard power transmitted through the majority of American households. As you can see, the single phase is a rather wide spread wavelength. Now, imagine the diagrams as representing horizontal springs. As a workload is applied, it gets harder and harder fort he generated current to maintain its shape, and it flattens out under load.

Now, look at the graph on the right that is three phase power. Imagine that as the same analogy used above. That same load applied to the now three horizontal springs is much harder to compress under the same load. In short, three phase uses three offset electrical currents that allows for a more powerful, efficient and refined system.

So what are the benefits?
The benefits of three phase power when considered in comparison to single phase power are obvious. Single phase motors use capacitors and windings to help the motor start and run, while three phase has simply the stator and windings. This makes for a less complex and more robust motor, with fewer things that can break and go wrong. Say you have a Three Phase Radial Arm Saw, due to the higher efficiency, it requires less conductive material to construct, making for a smaller, lighter motor with the same power as its larger single phase cousin.Amperage also plays a key part. For example, a 5HP table saw at 230 volts draws a maximum of 24 amps on single phase. The same saw equipped with a 5HP 230 volt three phase motor draws only 13 amps, almost half the power required for the single phase version. And with certain three phase motors, they may be wired for 440/460 volt three phase for a total of only a 6 amp draw, that’s less than a handheld belt sander.

Three phase power also makes reversing and speed control of three phase motors much easier. The simplicity of three phase motors allows them to be easily reversed up to simply switching two wires inside the connection box. Speed variation is also efficiently done with a variable frequency drive (VFD)

What are the drawbacks?
Although three phase power has its advantages, there is a downside, mostly for us Americans. Three phase power is typically not run in residential areas, making it problematic for the home shop owner, but not completely impossible.
What are my options?
There are a few ways to drum up three phase power. The first and most obvious is to have the power company run it to your house. If you live near an industrial area that has three phase, it can be run from their building to theirs, however this is usually the most expensive option, and by having to purchase the wire hand have the power company do the installation work, cost is rather high.

Kay MA-4 Phasemaster Rotary Type Phase Converter
Kay MA-4 Phasemaster Rotary Type Phase Converter

The most sensible option is a rotary phase converter (RPC). A RPC takes in single phase 230 volt current and puts out 230 volt three phase current. RPCs are usually a bit expensive, but in many cases, far cheaper than having the wire run from the grid. There are also ways to build your own RPC; however, it is not for the faint of heart, as it requires a lot of work and electrical knowledge. Another alternative is to install a VFD, this allows you to run three phase machines off of single phase power, and is practical if you only have a machine or two. The last and least favored alternative is the static phase converter. Static converters take single phase power and split it to run two of the legs. The third leg is then generated by capacitors until the motor is started, and then the capacitor drops off, leaving the motor to run only at two thirds of its rated power. These are the least favorable of the bunch, and certain manufacturers will void your machine warranty if you use one.

So what’s the verdict?
In short, if you’re looking for economical and efficient power supply, three phase is the way to go, especially in industrial applications. But, like all things, consideration and planning is required before you make a move.

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