 However, current still flows even when a system is out-of-phase, which causes transmission lines to heat up due to current flow.Consequently, transmission lines can only heat up so much (or else they would physically sag too much, due to the heat expanding the metal transmission lines), so transmission line operators have a "ceiling" on the amount of current that can flow through a given line, and excessive inductive reactance can limit the power capacity of a line.Power providers utilize capacitors to shift the phase and minimize the losses, based on usage patterns.