A method and device for the non-intrusive determination of the electrical power consumed by a subscriber installation. From the sampled values of the supply current and supply voltage that are delivered to the installation, constituting a consumption signal, the sampled values are grouped in successive observation time windows; the poles and residues of the consumption signal are discriminated in each current window using the pencil method, the set of poles and residues associated with at least one singular value representing a combination of signatures of separate electrical loads; at least the active power consumed by a subset of electrical loads in operation is calculated, over at least the duration of the current observation window, the sum of the active powers consumed by each electrical load satisfying a consumed power function linking these poles and residues.