What might cause a chipped insert of pantograph's graphite?
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Correct answer
B. A rockinmg of the overhead line.
Explanation
In the photo you can see a tram pantograph touching the contact wire of the overhead contact line. A chipped graphite contact strip on the pantograph may cause the overhead contact line to swing - answer B.
A chipped contact strip has an uneven surface, which catches on the contact wire and pulls it as the tram passes. The wire starts to swing, and in an extreme case it may break. The contact strip does not affect the rolling resistance of the wheels (answer A) or how the batteries work (answer C). A damaged contact strip must be reported, and the tram must be sent for repair. The tram driver checks the condition of the contact strips before leaving by looking at the pantograph, and reports any damage to the technical staff.
Legal basis: Art. 66 para. 1 point 1 of the Road Traffic Act (Prawo o ruchu drogowym)