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I discovered this while waiting for the train to arrive in the Washington, D.C. Amtrak station. It looks like this has been this way for a long time. Someone should have enclosed these exposed wires in a junction box, or removed them altogether, a long time ago. As per 300.15 [Boxes, Conduit Bodies, or Fittings — Where Required], "Where the wiring method is conduit, tubing, Type AC cable, Type MC cable, Type MI cable, nonmetallic-sheathed cable, or other cables, a box or conduit body shall be installed at each conductor splice point, outlet point, switch point, junction point, termination point, or pull point, unless otherwise permitted in 300.15(A) through (M)."