In a previous question I was told that the Lorentz force can compute the force on charges in one system A from electric and magnetic fields from another system B, but A cannot be the same system as B because then self interaction terms would create infinitely huge energies. (Please let me know if it is possible despite the infinities)
So how is the Lorentz force law used in e.g. network models of a circuit? What parts gets to generate electric/magnetic fields and what parts gets to have charges?