single-phase vs. three-phase power

single-phase vs. three-phase power

June 10, 2024

Three-phase vs single-phase which do you want and why?

It all comes down to Amps, how many do you have, how many do you need and how many can you save? 

What power do you have? 

Everyone has single-phase power, the question is how big is your service? And, what are you running? The average service is 400 Amps up to 800 Amps in a box. We have seen more, but 400 Amps is the normal panel supply. Single-phase units draw more Amps. 

  • Why do you want single-phase equipment? Generally it requires less upfront cost, and is what you already have. However, single-phase units require more maintenance. 
Not everyone has three-phase power

The price ranges we normally see to add three-phase power can be as low as $10,000 and up to $50,000 on average. Some places we have seen $150,000 installs, depending on how much you need and where you are on the power grid. 

  • Why do you want three-phase equipment? It draws up to 40% less Amps compared to comparable single-phase equipment while delivering the same power output, and it lasts longer. 
The equipment limits for single-phase

The biggest single-phase compressors available are 5HP, and we can put them in series to make 10HP. But you will need the Amps to run the system. We build a ton of single-phase units in 5HP and 10HP configurations where three-phase just isn't an option. 

If you need more than 10HP you need three-phase. (it is possible to go bigger than 10hp but not cheap or done often) 

What about phase converters? 

Yep we see them all the time and they do work, but can have inconsistent amperage and voltage output. If you are planning on using a phase converter make sure the equipment can handle the slight voltage and amperage inconsistencies. Tanktemp Chillers are engineered for this, but a lot aren’t. You will want phase protection on your equipment.

Phase converters are a good common solution to add three-phase power for a reasonable price or where three-phase is not an option, however, grid power is just better if you can. 

We are happy to talk with you about all these options and guide you to the best solution for you.

How big of a converter do I need?  

We are back to the Amp rating/service of your power provider.

There is actually not too much information that is needed when it comes to sizing a phase converter. All that is needed is the type of machine it is, the machines power requirements (this will be listed in HP, AMPs, kW, or kVA), and the voltage listed. There are different types of phase converters that are designed for different style loads. There are phase converters set up for light-duty loads, CNC, resistive, and hard starting loads. Each load runs different and has different starting loads. Going over the type of machine will help determine which phase converter will work best. One thing to keep in mind, there is no harm in going with a phase converter for a larger load even if your current load does not require it. It is better to go bigger now than find out later that you need it.

A general and quick rule of thumb when sizing a phase converter is that when looking at the HP rating of your machine, you want to double that to get the size phase converter that is needed. For example, if you have a 10 HP motor then a 20 HP phase converter is needed. This is related to the start load of a machine and the fact that you are pulling from single phase power to operate a three-phase machine. However, there are exceptions to this rule but during your first planning stages of looking at a phase converter, this will give you an idea to help budget and plan towards.

The most common phase converters are rotary phase converters. What is a Rotary Phase Converter?

Simply put, a rotary phase converter uses an induction generator motor, in that it rotates to transform single-phase utility power into three-phase electricity. A rotary phase converter generates one line of power from the induction generator motor and merges that with two single-phase lines. Rotary Phase Converters produce alternating-current electric power to operate three-phase equipment such as motors, inductive and resistive loads. Rotary Phase Converters provide three-phase electric power where it may be hard to get or too expensive.

How Does a Rotary Phase Converter Work?

By acting as a rotating generator, rotary phase converters transform the single-phase energy supply into three-phase power. The rotary phase converter uses a single-phase two-line supply of power from the utility, and creates a third line of power. The three lines, also known as phases, are indistinguishable to utility three-phase power, typically more accurate than utility-supplied three-phase power, with all three lines shifted 120 degrees. When the rotary phase converter is properly sized, it will produce true three-phase power with each of the three output voltages well balanced over the entire range of connected loads.

To calculate what input power is needed, the square root of three (1.732) is used as a multiplier of the three-phase current value found on the motor data plate. The resulting value is the amount of power, expressed in amps, required at the input side of the phase converter. There is a lot more to this, but this is the basics.

Example of the equation:

You’re preparing to drive a three phase low-horsepower motor rated at 10 amps. Single-phase to three-phase power calculation input requirement = The square root of 3 (1.732) x 10 amps  = 1.732 x 10 amps = 17.32 Amps. Single phase power input in this instance is 17.32 Amps

Back to your panel box, how much power do you have in that box for this equipment? 

Advantages of three-phase equipment

Power Efficient

Three-Phase equipment draws up to 40% less Amps compared to a single phase equipment to deliver the same power output. This means that compared to a single-phase machine, a three-phase machine can achieve the same tonnage while pulling less amperage.  

Fewer points of failure

Three-phase motors have lots of starting torque and don't require any special circuitry to start (capacitors, centrifugal switches, like 1-phase systems). And of course fewer components means fewer things to go wrong. 

Longer equipment life

Due to three-phase power creating a more balanced flow of electricity, the electric motors in refrigeration compressors run smoother with less vibrations. The more balanced and smooth the motor runs, the longer the compressor will run without maintenance.

Common issues with three-phase power

Some issues with three-phase power are phase reversal, phase loss, or low voltage drops. If one of the legs is lost it can result in the electric motor being burned up. Low voltage can also result in irregular running conditions pulling high amperage, tripping breakers, or burning up fuses. Lastly, if there is a phase reversal the motor can run backwards. This will give the appearance of a system running but not working correctly. Equipment running backwards can result in damage to the motor or compressor from these conditions if left for too long. 

All three-phase units should be installed by a tech to ensure proper phasing of the unit and they can test high side and low side pressure to assure these are correct. Phase protection will also help eliminate any of the three previously listed potential problems of power. 


Overall three-phase power offers a more reliable and power efficient option. Along with everything we’ve discussed, the following should also be considered when deciding on single-phase vs. three-phase power.

  • What are the daily hours of operations? Longer hours of operation make the additional investments in the 3-phase system a better choice.
  • Is three-phase supply readily available? If not, then laying out and installing new wiring will add significantly to the initial cost.
  • Additional equipment such as voltage conditioners, phase monitors, etc become necessary based on the local electric supply conditions. Cost of these additional components must be added to the overall initial cost.
  • Given these factors, three-phase equipment is often recommended to customers who expect longer running hours. 
Tanktemp Notes
  • Most equipment we build under 3 horsepower is single-phase. 
  • About 28% of the 5HP and 5X5 units we build are single phase. If you don’t have three-phase we can work around it. 
  • Single phase units that require heat do pull a lot more Amps. 
  • If you are on a phase converter and looking at these size units we generally, though not alway, suggest the single-phase options depending on the cost to bring in three-phase. We are always going to like three-phase better for these type units but will talk with you about your location, building, budget and overall needs. We understand the power grids that a lot of wineries are on, and the other equipment needs on the production side. 
  • This is one of the many advantages of working with Tanktemp. Over the last 45 years we have learned exactly how your production side functions.

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