(Often the sections are run with different voltages or frequencies.) The grids could be synchronised on a normal basis, but activities might interrupt synchronisation. This is not a problem for DC devices. AC programs have a selected basic safety implication in that the railway electrification method would act as a "Backdoor" connection in between

Trolleybuses use a next parallel overhead line with the return, and two trolley poles, one making contact with Every single overhead wire. (Pantographs are normally incompatible with parallel overhead traces.) The circuit is concluded by utilizing the two wires. Parallel overhead wires are made use of around the uncommon railways with three-phase A