# 3 phase power formula

Discussion in 'Electronic Basics' started by erthlink, Feb 25, 2004.

the three phase power formula goes like this:

V * I * 1.732 * PF

where V - voltage, I - current, PF - power factor

a 3 phase generator set to 120/208 V with amperage values of 24A, 26A, 22A
at each phase.. PF is 0.8

which V value should i use? do i take the average current (I) or do i add
them up?

2. ### John PopelishGuest

If the three currents listed are the 3 line to neutral currents (not
line to line current) then you just use the single phase formula 3
times and add the results. 120V*A*PF

3. ### Lord ErdelGuest

which brings me to another question.. what am i measuring when i use a
clamp-on ammeter? am i correct in stating this equation then?

P = V[phase-ground] * ( I[phase1] + I[phase2] + I[phase3]) * PF * 1.732

assuming i have the same phase voltages across the board of course..

4. ### Don KellyGuest

If the currents are the same in all 3 phases then use the line to line
voltage (208V). Otherwise use 120*I*pf 3 times and add them up as John has
indicated. Actually using 208*1.732*24A*pf will probalby be close enough for
government work.

5. ### Guest

| the three phase power formula goes like this:
|
| V * I * 1.732 * PF
|
| where V - voltage, I - current, PF - power factor
|
| a 3 phase generator set to 120/208 V with amperage values of 24A, 26A, 22A
| at each phase.. PF is 0.8
|
| which V value should i use? do i take the average current (I) or do i add
| them up?

Is that 0.8 PF the rating of the generator, or the actual load?

6. ### Lord ErdelGuest

0.8 is my arbitrary value for PF..