When measuring power in a 3-phase 3-wire system using the two-wattmeter method, both wattmeters read equal positive values when load power factor is:
AUnity (1.0)
BZero
C0.866 leading
D0.5 lagging
Explanation
At unity power factor (phi = 0°), both wattmeters read W1 = W2 = V_L * I_L * cos(30°) = sqrt(3)/2 * V_L * I_L.

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