Portal:Trains/Featured picture/Week 22, 2006
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Sparks fly from the electrification system on the London Underground.
The London Underground uses a 4-rail system in which the electrical return is isolated from the running rails (the rails used by the train's wheels). Sparks like this are quite normal and occur when the electric power collection "shoes" of a train that is motoring (i.e. drawing power) reaches the end of a section of electric power rail.
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