The impact of direct current differs from the alternate current, which manifests itself. There are direct current lines in the underground, which, in theory, may be broken at unexpected circumstances. What to do then?
Question of people protection from ocassional direct current impact in the subway is the crucial issue when making the plan of stations.
If a person is hit by a direct current, he might be unable to percieve that it is in danger, unlike alternate current, the direct current doesn't "bite", it "heats" the internal organs of the human body. The first thing the injured person will feel is warming.
What measures are taken in order not to subject passengers and underground workers to voltage? The first thing to do is fulfil grounding and equipotential bonding.
In accordance with the regulations 120.13330.2012, p.220.127.116.11, it is necessary to foresee the uniform system of protective grounding. Usually, natural ground electrodes are used for grounding, in particular, these are reinforced concrete structures, cast iron tunnel casing, various fastening metal structures and also ordinary artificial ground electrodes of module type corresponding to rules, to EIC 7th edition and GOST R 50571.5.54-2013.
All metal stairs, trays, structures, equipment and others must have a direct connection with the uniform grounding system. Ground conductors must be corrosion resistant and must not be subject to mechanic impact and also there should be an access to the places of conductors' connection for a visual inspection and holding measurements of the transient resistance (steel-to-steel contact).
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