Main fuse

The main fuse is a miscellaneous item added to Fallout 3 in the Broken Steel add-on.

Overview
The main fuse is a quest item added in Broken Steel. On the quest Who Dares Wins, a broken fuse box is found that activates the train to the left. A robot named Presidential metro sentinel unit is carrying it in its inventory and it is required to fix the train. Should the robot survive the ghoul attack during the quest, it will eventually replace the fuse box itself, a rather easy workaround of it falling through the ground (see Bugs below for details).

Related quests
Who Dares Wins: Go to the Presidential Metro and fix the train sitting in the station, then report back to the Brotherhood of Steel.

Bugs
After clearing the area of all ghouls, the (optional) quest of containing the security breach may not trigger as complete, so the sentry bot with the fuse does not complete repairs.
 * To fix, either reload a save or just kill the sentry bot and do the repairs yourself and then the quest will finish. Having companions wait out of range may also help.

Hauptsicherung Главный предохранитель