Power measurement with 2 Wattmeters?

[usernam]

Are there any advantages of the 2 wattmeter method for measuring power as compared to using 3 wattmeters? (Apart from the obvious one that less wattmeters are needed)
Also are there any disadvantages?

 

[mrniceguy]

The biggest advantage comes from needing less wattmeters, and introduce less meter loading on your circuit (because as you know ANY meter will load the system to some degree)

The main disadvantage, the 2 meter system only works on 3wire systems, a 4wire system requires 3 meters.

For more info on why it works and what not try hxxp://www.ohiosemitronics.com/pdf/tech_papers/Two-wattmeter-method(E).pdf