What most often cause loss of start-up?
Show the correct answer
Correct answer
A. Tram power failure (e.g. loss of overhead connection or a tram stop "on the insulator").
Explanation
The question is about the most common cause of loss of start-up, that is a situation in which the tram stops accelerating even though drive is switched on. Most often it is a lack of power, for example a loss of voltage in the overhead contact line or the tram stopping "on the insulator" - answer A.
The traction motors take current from the overhead contact line through the pantograph. When there is no voltage in the line or the pantograph stops under a section insulator, which does not conduct current, the tram loses power and stops accelerating or cannot move off. The internal lighting (answer B) is powered from a different circuit and has no effect on starting. Weather conditions (answer C) can make moving off harder, for example because of wheel slip, but they are not the most common cause of loss of start-up. That is why you do not stop the tram under an insulator, and when voltage is lost, you inform the dispatcher.
Legal basis: Art. 3 para. 1 of the Road Traffic Act (Prawo o ruchu drogowym)