What is the colour of the power cable in trailers with a two-circuit pneumatic braking system?
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Correct answer
A. Red.
Explanation
In the photo, there is a red two-axle trailer with a yellow grille guard, adapted to be pulled by an agricultural tractor. In a two-line air brake system, the supply line is red - answer A.
The two-line air connection between a tractor and a trailer is made up of two lines whose coupling heads differ in colour and in the shape of their protective cover, so that they cannot be confused. The red supply line constantly delivers compressed air to the trailer's air tank, and the yellow one (answer B) is the control line, which transmits the braking signal when you press the pedal. Black (answer C) usually indicates an older single-line system, allowed as an additional connector. Make sure that each coupling head is clean, has an undamaged seal and is properly latched - a leaking connection weakens the trailer's braking. When connecting the trailer, you first connect the yellow line, then the red one; when disconnecting - first the red one, then the yellow one.
Legal basis: § 49 para. 2 of the Regulation on the technical conditions of vehicles and the scope of their necessary equipment; colour coding of coupling heads according to ISO 1728