# Calculate Power of 3 Phase HVAC Unit

I have an HVAC unit and I know the phase 1 current, phase 2 current and phase 3 current. I know the voltage of the unit, from this, how can I calculate the power used by the entire unit?

Further information, does the HVAC unit have 3 separate voltages for 3 phase? I know for example, the one on my roof is 230 volts and it is 3 phase. Does that mean that I can use a voltage of 230 for calculating the power of each of the phases?

If you want apparent power its the sum $V_aI_a + V_bI_b+V_cI_c$. In the USA each phase is 120/208v (relative to ground/relative to neighboring phases). Assuming you're measuring with say a clamp meter over each phase of the power cable you'd use 120v and not 208 as your V.

If you want real power then you are out of luck unless you can measure phase. In which case it's the same equations but the above are complex values.

three phase power is the summation of the VA

ie $V_a*I_a + V_b*I_b + V_c*I_c$

Where $V_{a,b,c}$ are phase rms voltages in a star arrangement & $I_{a,b,c}$ are the associated phase rms currents

This can be simplified down to $P_{3\Phi} = V*I$ for a balanced load

• to make a complete answer for myself and other viewers, would it be possible that you show how to calculate the the RMS voltages and RMS current values Jul 6, 2015 at 1:13