The principle of power preservation is applicable to both ac and dc circuits. This principle, when applied to AC power, asserts that the complex, real, and reactive powers produced by the source are equal to the total complex, real, and reactive powers absorbed by the loads. When two load impedances are connected in parallel to an ac source V, the complex power provided by the source can be calculated using the relation

where S₁ and S₂ represent the complex powers delivered to loads Z₁ and Z₂ respectively. If these loads are connected in series with the voltage source, the complex power supplied by the source remains unchanged. This suggests that regardless of whether the loads are connected in series or parallel (or in any other configuration), the total power provided by the source is equal to the total power received by the load. In general, for a source connected to N loads, the complex power is given by

This implies that the total complex power in a network is the sum of the complex powers of its individual components. This holds true for real power and reactive power, but not for apparent power. This articulates the principle of AC power conservation. From this, it can be deduced that the real (or reactive) power flow from sources in a network equals the real (or reactive) power flow into the other components of the network.