BPC stands for 'Brake Power Certificate'. It is a written document certifying that the rake has passed the brake continuity test and that the brake system of the entire rake is in perfect working order. It is usually issued by the Coach maintenance yard before the beginning of the journey.
The BPC is only valid for a fixed distance and running time that is specified in the document by the maintenance yard. If the rake runs for a longer distance or runs for more time, then a new BPC has to be issued after the expiry of the old one.
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more... In this case, they are ensuring that there is no delay in letting the incoming rake from MAS to depart to BKN by issuing a BPC right from MAS till BKN via KCVL. Normally, KCVL would have had to provide a new BPC before the start of the journey.