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Why does the third rail change sides?

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MartinR:
Those huts may simply be platelayers' huts where track maintenance equipment is stored and platelayers can seek shelter/have a brew.  I think most switchgear is trackside rather than in a building, but I may be wrong in this.  You're quite right that it is a DC system: 750 VDC.

John Walker:
Thanks for the explanations.  When traveling on a train, you see a section of third rail appear on the offside at regular intervals once you get out into the countryside.  There always seems to be a small building around the halfway mark.  Could it also be where the current is boosted as I believe it's a DC current?

MartinR:
The third rail is usually outside the tracks on normal double line, but inside in stations etc.  This is a safety issue, the so-called 8' 6' is the gap between two running tracks.  If crossing the tracks it is better to have the hazards of the third rails well separated and in an emergency it is safe to lie there.  Within stations you want the rail as far from the muppets passengers as possible.  turning to the observed brief changes of side, I believe this is so that sections of track can be de-energised.  You also do not want a the pickups on the front of a train to energise the rail from the pickups at the back.  Therefore to work safely on a section, de-energise it and the two short linking sections either end.  Of course no train should be attempting to enter a section where there is an engineer's possession, but accidents do happen.

mmitch:
Usually its points. But I suspect it is also to even out wear on the pickup shoes.
Interesting when crossing a set of sidings, but that was many years ago!
mmitch.

John Walker:
I've noticed that every so often, the third rail switches to the outside for a short section. 

Can any of our railway-buff members tell me why?

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