The current in a.c. circuit is said to be wattles if the average power consumed in the circuit is zero.
The average power of an a.c. circuit is given by
The current Irms can be resolved into two components:
- Component Irms cosϕ along Erms . As the phase angle between Irms cosϕ and Erms is zero. therefore
- Component Irms sinϕ normal to Erms . As the phase angle between Irms sinϕ and Erms is π/2. Therefore
We call the component Irms sinϕ as the idle or wattles current because it does not consume any power in a.c. circuit.