Usually a high voltage is carried by the overhead-wire system, and the third rail has current at a much lower voltage. This is because of the danger that a man on the line might touch the electric rail, but he can not touch an overhead wire.

• 通常高压电被高架线系统输送，第三根铁轨里的电压则是很低的，这是因为如果一个站在线路上的人就可能碰到电轨，那是很危险的，但是他不可能碰到高架线。