The main reason for using the fourth rail to carry the return current is to avoid this current flowing through the original metal tunnel linings which were never intended to carry current, and which would suffer electrolytic corrosion should such currents flow in them.
42.
On the track, a third rail of high conductivity steel was laid outside the four-foot; the return current travelled through the running rails; impedance bonds were provided at track circuit joints, and the track circuits had to be altered to a . c . operation.
43.
The ground is a precaution in case a fault starts leaking current to the metal body, but in normal operation it shouldn't be leaking at all and the neutral line should handle the entire return current . talk ) 12 : 51, 29 July 2014 ( UTC)
44.
Trams using trolley-pole current collection are normally powered through a single pole, with return current earthed through the steel wheels and rails, though some systems ( e . g . parts of the London system ), used twin overhead wires and poles to avoid the effects of stray currents flowing through the earth.
45.
For a wire near a flat surface sheet or block conductor carrying the return current, the return current tends to follow the path nearest the wire, however it may be routed, and not go through the path of least resistance ( ie the direct point to point path ) . talk ) 17 : 57, 6 May 2014 ( UTC)
46.
For a wire near a flat surface sheet or block conductor carrying the return current, the return current tends to follow the path nearest the wire, however it may be routed, and not go through the path of least resistance ( ie the direct point to point path ) . talk ) 17 : 57, 6 May 2014 ( UTC)
47.
Maintenance outages are planned well in advance to minimise the effects they are usually carried out in summer when national electricity demand is at its lowest, and on only one pole at a time, with the other pole remaining in operation providing half of the full two-pole capacity, utilizing the earth electrodes providing a path for return current through the ground.
