# How to calculate cost of running 3 phase motors

Users often ask how much electrical cost they will experience operating a pump or aerator motor. The basic formula to calculate electric cost per hour is. Cost per day, week, month, year, etc then depends on how many hours the motor is operated in that timeframe. You can still come close, but you will have to calculate the Kilowatt Rating using the following formula.

The formula varies depending if the motor is 1-Phase or 3-Phase.

## 3 Phase AC Motor Starting & Running Current Calculator

How do you know? The motor plate should tell you that or your electrician can tell you. Power Factors:. You may want to Look at your last example thoroughly. Unless, there are single phase operating at in your area.

### Calculating cost of running electric motor?

Save my name, email, and website in this browser for the next time I comment. Index Prev Next Share. Find on motor label or in manufacturer literature. Find on a recent bill or call them. You can still come close, but you will have to calculate the Kilowatt Rating using the following formula; The formula varies depending if the motor is 1-Phase or 3-Phase.

Find on motor label plate or measure with an Amp meter. Find on the motor label plate or measure with a Volt meter. Find on motor label plate or estimate with following table.For a 3-phase motor the procedure is as follows: 1 Measure all three phase-to-phase voltages and average them. This will give you an average of volts. We measure 41, 42, and 43 amps, giving you an average of 42 amps. Do this by choosing the motor power curve closest in value to the rating of your motor.

Third, calculate the input power in kW. First, figure out how much each kWh costs — by taking a recent electricity bill and dividing the total dollar amount including taxes by the total number of kWh consumed during the billing period. Second, multiply this number times the kWh value calculated in step 5 above — this will give the approx. In our example, if the average cost of kWh is NOTE: If you see a way to reduce the load on the motor or reduce its running time, you may want to know how much you will save.

Motors that are built into commercial equipment tend to be properly sized, but other motors may not be. For one thing, motors are often specified to have more horsepower than is actually required.

These underloaded motors cost more to run than properly loaded ones because they operate on a less efficient part of their load curve. At the other extreme, some motors are called upon to deliver more power than they are designed to deliver.

They will do this for a while, bt they overheat and eventually fail. Here, longer-term data gathering is needed, using a device known as a recording wattmeter. Calculating What it Costs to Run a Motor. March 30, Posted in Uncategorized. JP Motors.The Wall. Click here to Find a Contractor in your area. Here are the website rules, as well as some tips for using this forum. If you've found help here, check back in to let us know how everything worked out.

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3 phase motor test

Timco Member Posts: 2, Mark Eatherton Member Posts: 5, February Hi Tim I think it depends upon the phases. Borrowed from Heatboy. Costs This is a 3-phase building but motors are 2-pole. We used to call that 2-phase to denote 2-phases of a 3-phase system rather than calling it single phase 2-pole. I wasn't converting to KWH.

Paul48 Member Posts: 4, February edited February Watts watts to 1 HP. Regardless of voltage. Thanks Mark Didn't have a calculator handy.

Does that take into account 2-phases? Then we divide by the inverse. Looking more like Tim's numbers. Motor duty It runs an air handler. V x A Mark, how did you come up with that number? With an inductive load like a motor, you cant just multiply volts times amps without taking the power factor into account.

So phases don't matter? Phases etc. The type of motor or the number of phases doesn't matter in the wattage calculation.The three phase electric motor is usually a large piece of equipment that uses a "polyphase" circuit to draw heavy power loads at relatively low voltages. This improves power line efficiency and provides the smooth power flow required by many such motors. The cost of electricity for electric motor three phase operation is based on the kilowatt hours used, just like any other electrical device.

However, figuring power usage is more complicated because the conventional equation for power usage must be modified to apply to three phase motors. Find the voltage and amperage used by the three phase electric motor. The line voltage will be given by the manufacturer's specifications. Most such motors have readouts for the amperage. If that's not the case, use an ammeter designed to handle three phase currents to measure the amperage.

Follow the ammeter manufacturer's instructions for hooking the ammeter into the power line to measure amperes. Calculate the power the motor consumes while in operation. W is the power consumption in watts.

For example, if the electric motor uses 50 amps at volts, the wattage is 50 x x 1. Record the time the motor is in operation. For example, in a manufacturing plant, a three phase electric motor might run 8 hours a day, 5 days a week. This works out to an average of Multiply the power consumption by the hours of operation to find kilowatt hours. A 3 phase electric motor drawing Multiply the total kilowatt hours used by the rate per kilowatt hour charged by the power company to find the cost.

For instance, the cost of electricity for three phase motor consuming He writes about business, personal finance and careers. Adkins holds master's degrees in history and sociology from Georgia State University. He became a member of the Society of Professional Journalists in Written by: William Adkins Written on: February 04, References All About Circuits: 3 phase power systems.

About the Author. Photo Credits Getty Images.Log In. Keith Cress Flamin Systems, Inc. This assumes a balance loadthat is equal curent in all three lines. A motor would be such load for all practical purpose. You can use a reasonable assumption of 0.

This will give you a fairly accurate results for your purpose but not precise. If you really need to get more precise, you need a meter as suggested before. I believe more in accuracy than precision for cost comparisons. An easier and often more accurate reading may often be obtained using the kh factor of the meter.

It is quite easy on the older electro-mechanical meters. It is more difficult on an electronic meter. Step one. Time about 10 or 20 turns of the meter disk. Step two. Calculate the number of turns that the disk would make in an hour. Step three. Look on the face of the meter for the kh factor. The kh is the number of watt-hours for one turn of the meter disk. Step four. Multipy the kh factor by the number of turns per hour. Step five. Divide by to convert watt-hours to kilowatt-hours.

Rather than measure motor lead current, using a strobe light, measure the amount of slip in the shaft speed. This will be in direct proportion to the nameplate hp. That will give you a measure of how heavily the motor is loaded. Of course, this assumes a reasonably constant load. The shaft speed is measured at rpm. This is 30 rpm slip on a motor rated at 40rpm slip at full load. That would be 75hp on this motor. Let's say that your electricity costs are actually 12 cents per kwhr.

### How to Calculate 3 Phase Motor Power Consumption

I'm sure the purists will have plenty of reason to pick this apart but, for estimating purposes, it is simple and reasonably accurate. For kW divide W by I did not know, figuring cost of energy for a motor was that complicated. Any margin of error corrected by placing a meter etc. Assume 0. That should get you quite close assuming you have a constant speed motor with a more-or-less constant load. I see no reason to get much more complicated than that. As the power factor changes with load changes, the calculations for a motor running at less than full load get more complicated whether you see the reason or not.

With most facilities I would typically do any work in, it would be nearly impossible to use the utility meter method, as it would be nearly impossible to know the difference you are observing at the meter only corresponds to the motor in question as so many of the other loads in the plant would be varying continuously.Users often ask how much electrical cost they will experience operating a pump or aerator motor.

Cost per day, week, month, year, etc then depends on how many hours the motor is operated in that timeframe.

You can still come close, but you will have to calculate the Kilowatt Rating using the following formula. The formula varies depending if the motor is 1-Phase or 3-Phase. How do you know?

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Calculating Motor Run Cost. Send email Mail. Share on Facebook Share. Share on Twitter Tweet. Share on Linkedin Share. Share on Google Plus Share. Share on Digg Share. Share on Pinterest Share. Share on Whatsapp Share. Print this Print. Find on motor label or in manufacturer literature. Find on a recent bill or call them. You can still come close, but you will have to calculate the Kilowatt Rating using the following formula; The formula varies depending if the motor is 1-Phase or 3-Phase.

Find on motor label plate or measure with an Amp meter. Find on the motor label plate or measure with a Volt meter.Three-phase circuits distribute electrical power along multiple conductors in the same power line. The current waveform of each conductor is offset in time from the others. This allows more power to be transmitted on one line at a lower voltage, increasing efficiency without sacrificing safety. For three-phase motors, there is an added advantage: the three-phase power supply provides a smoother waveform in effect, a more balanced supply of electricity.

Understand the difference in how power consumption is calculated for conventional and three-phase power circuits. In a conventional electric circuit, power in watts is equal to the voltage multiplied by the amperage. For a three-phase circuit, watts equal volts times amperes times the square root of 3.

Determine the voltage and amperage when the motor is running. Most three-phase motors are large devices and have their own readouts. However, you can measure the current amperes in some cases.

An ammeter rated for three-phase applications will do the job and works much like an ordinary ammeter. You plug the motor into the ammeter and the ammeter into the power line. For example, if the motor is drawing 30 amps at volts, you have 30 x x sqrt 3 about 1. Convert watts to kilowatts by dividing the number of watts by 1, Thus, a three-phase electric motor drawing 12, watts is consuming For one hour, this equals This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.