[en] The incident at Bugey 5 on 14th April 1984, which is regarded as one of the most important in recent years has alas shown again that unless dealt with by the operators in good time, failure of a rectifier supplying one of the buses may soon lead to a very serious situation, in this particular instance voltage loss on the train A 48 volt supply from the two offsite electrical sources and train A diesel generator. Operating experience feedback of the past three years reveals that although the Bugey incident is undoubtedly the most serious, it is not the only where a major alarm was not taken into consideration until fairly late by the operators, and other types of error with far from negligible consequences have occurred during repair work on buses. After a brief reminder of the role and layout of buses, statistics of all incidents of this type in recent years are described and a few cases are presented in order to give some idea of the range of situations encountered. The main measures aimed at reducing the number of incidents of this type are then presented, bearing in mind that one cannot hope to remove the possibility of this type of failure entirely. It may also be noted that the large number of such errors during the night shift or at the very beginning of the morning shift is no doubt connected with the well-known fact that operators are less vigilant at such times