Résumé : The company Elia, which manages the grid system of electricity in Belgium, is mainly controlled by the principal producer of electricity, Electrabel, and by political powers. The Belgian state has recently constrained the French group to yield 3% of its stake in Elia as foreseen in the Pax Electrica agreements. This article studies the impact of this transfer by means of the Banzhaf index that measures the intensity of control. The results show that theoretically these agreements change the power relationship on the manager of the grid.