Signalling Power
Usually, signals and other equipment (such as track circuits and level crossing equipment), are powered from a low voltage supply. The specific voltage varies with the country and equipment used. The reason behind this is that the low voltage allows easy operation from storage batteries and indeed, in some parts of the world (and previously in many more locations, before the widespread adoption of electricity), batteries are the primary power source, as mains power may be unavailable at that location. In urban built-up areas, the trend is now to power signal equipment directly from mains power, with batteries only as backup.
Read more about this topic: Railway Signal
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