The invention relates to a controlling system (4) for controlling loads (2), especially lighting units, of a power/data-communication system like a PoE system, wherein a command is provided, which defines desired power levels of loads of the power/data-communication system. An overall power change amount is determined, which will be caused by the provided command, and the loads are controlled such that the slope of the overall power consumption of the loads, when being set to the desired power levels, is reduced, if the determined overall power change amount is larger than a predefined power change threshold. Thus, if the provided command may lead to an overall power change amount causing problems like blown fuses, the loads are controlled such that the slope of the overall power consumption of the loads, when being set to the desired power levels, and hence the likelihood of, for instance, blown fuses is reduced.