I have a single phase load (90 A 230 V) and 2 three phase loads (7 kW 400 V 3 phase/9 kW 400 V 3ph+N) connected at the same time to a three phase network.

How the 3 phase calculations (line current of each load, total line current) done in this case?

Are there any documents you recommend?

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Obviously the single phase load draw 90 A from the line W.

For the three phase load 7 kW the current drawn by each line is:

I(U,V,W)= (7000)/(400*sqrt(3)*0.8) = 10 A

For the three phase load 9 kW the current drawn by each line is

I(U,V,W)= (9000)/(400*sqrt(3)*0.8) = 16.2 A

Total current drived by each line:

IU=10+16.2=26.2 A

IV=10+16.2= 26.2 A

IW=10+16.2+90= 116.2 A

  • \$\begingroup\$ Imagine the single phase load wasn't connected at all. Do you know how to do the 3-phase analysis? Then if only the single phase load were connected, do you know how to perform the single phase analysis? Please demonstrate that in your question. \$\endgroup\$
    – Andy aka
    Commented Dec 14, 2022 at 21:04
  • \$\begingroup\$ (Why consider the three-phase loads separately? Where do you get PF from?) \$\endgroup\$
    – greybeard
    Commented Dec 15, 2022 at 8:16
  • \$\begingroup\$ PF power factor = 0.8 \$\endgroup\$
    – Engineer
    Commented Dec 15, 2022 at 12:18
  • \$\begingroup\$ (10 A / 7) * 9 ≠ 16.2 A \$\endgroup\$
    – greybeard
    Commented Dec 15, 2022 at 21:34

1 Answer 1


You tried to use the power factor to turn the addition of currents into a scalar computation
(introducing an error with the 7 kW load).

Addition of AC load currents doesn't work this way even for linear/reactive ones.

I'd need to know whether current was leading or lagging voltage - for each load assumed uniform over all its phases.

Assuming the 3-phase loads either both capacitive or both inductive, the question remains underspecified in the single-phase load. (You can try to pull resistive/PF 1 out of thin air).


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