If the pantograph with the knuckle facing forward on a HST is defective what must be done?

• A. It will be raised and the rear knuckle lowered.
• B. Do nothing and continue.
• C. Lower both pantographs.
• D. It will be lowered and the Pantograph with the rearward facing knuckle raised.

Answer: (D)

When a pantograph is found defective, the safe approach is to isolate the faulty unit and rely on the other pantograph for current collection. On this HST, the correct procedure is to lower the pantograph whose knuckle faces forward (the defective one) and raise the pantograph whose knuckle faces rearward. This removes the faulty contact from the overhead wire and still provides power through the functioning pantograph, reducing the risk of arcing, wire damage, or mechanical interference that could occur if the damaged unit remained raised or if both were left in service. Lowering both would cut power entirely, and doing nothing would leave a damaged contact in place, both of which are unsafe.