In this paper new time invariant properties of PLC (Power Line Communication) channels are pointed out. First, we have obtained an equivalent lumped circuit that represents the transmission line characteristic of a power cable starting from the analytical solution of the telegrapher's equations. Then, the Y matrix has been employed to compute the transfer function between power network ports, taking into account load variations. The effect of a high number of branches in the network on transfer function diagrams is investigated. Both simulation and measurement show that in a complex power network (with several parallel connected branches) the time varying phenomenon of the transfer function, caused by the load on-off switching, is strongly reduced. A demonstration is here provided to support these results.