# 3 Phase Load Calculator



## Southeast Power (Jan 18, 2009)

Does anyone have a three-phase load calculator they would like to share?
I can find several single phase and have a couple I use but, three phase seems to be hard to find.


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## Incognito (Apr 14, 2019)

Southeast Power said:


> Does anyone have a three-phase load calculator they would like to share?
> I can find several single phase and have a couple I use but, three phase seems to be hard to find.


What do you mean? Like a program for doing load calc’s? Can’t you just divide the final wattage by the 3 phase voltage and get the load?


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## joebanana (Dec 21, 2010)

How about the formula? Full load amps = VxAx1.73/1000?


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## Southeast Power (Jan 18, 2009)

We use a fill in the blank sheet for residential load calculations. The one I have is on a spreadsheet. The first tab was residential, the second tab was 3 phase. 
I lost track of the original.
It was oversimplified but, I could populate the values, it calculated everything and I could print it out when needed for permits.

I think I'll use a three-phase panel schedule, auto sum the columns, and VxAx1.73/1000 that row.


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## Wardenclyffe (Jan 11, 2019)

Southeast Power said:


> Does anyone have a three-phase load calculator they would like to share?
> I can find several single phase and have a couple I use but, three phase seems to be hard to find.


https://www.jcalc.net/three-phase-power-calculator


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## sparkiez (Aug 1, 2015)

The load calc is just going to be a normal load calc (net sum of power). In order to get your circuit ampacity ( P/(1.73 * V) )


I'm thinking that 1000 is to bring the calculation from kilowatts to watts, and may not be necessary in your context. If that isn't what it is there for, please do correct me as I'm genuinely curious.


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## Dennis Alwon (May 9, 2009)

Almost all online calculators give the option to choose between single phase and 3 phases as well as copper or aluminum etc.

https://www.calculator.net/voltage-drop-calculator.html


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## Juhanson (Dec 22, 2017)

There are "Power->Current" and "Current->Power" calculators for 3-phase and 1-phase circuits in the MeteorSPEC. It is absolutely free toolkit for electricians You can find it on meteorspec.com


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## aathif61 (9 mo ago)

How to calculate breaker load


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## paulengr (Oct 8, 2017)

The big problem with three phase is that in commercial you will have to keep track of 3 single phase loads and in industrial motors drive everything. When sizing as a load calculation it is fairly straight forward. If it does it purely in amps you could use a single phase calculator because the results are the same. It’s only when you do kw/amps conversions that the single phase sheet fails.

For transformers and generators the starting current often drives everything. That’s where you need to have an estimate of %Z, LRC Codes, application settings for soft starts/drivesand a better transformer calculation that calculates %VD. Online calculators are just too simplified. The details quickly get away from those.

Just taking say a quarry crusher for an example most spreadsheets ASSUME LRC Code F. But crushers are often 8-10x FLA. if I start on a soft start they often assume 3x FLA which is valid with a pump but in a crusher it’s 6x FLA. And assuming HP plus 5 times the largest motor (LRC Code F) is true if you can space out motor starting and ignores the fact that you can easily overload transformers quite a bit temporarily so they will be oversized.

NEC is very rigid on load calcs for residential and works reasonably well. It pretty much fails on industrial and a lot of commercial loads because it’s all custom loads.


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