As shown in the illustrated electrically operated watertight door controller, by what action is the closing of the watertight door normally stopped when fully closed? See illustration EL-0115.
• Study how the Close pushbutton circuit feeds the coil marked C (close contactor). • Identify the roles of the two limit switches labeled LSO (open limit switch) and LSC (close limit switch). • Notice where the overload (OL) devices are placed and what part of the circuit they actually protect.
• When the door is traveling in the CLOSING direction, which limit switch will physically be reached by the door mechanism when it is fully closed? • If the close contactor coil C loses power, what in this diagram could cause that to happen right at the fully closed position? • Does the overload OL operate every time the door closes normally, or only under fault/overload conditions? How does that affect which choice is normal operation vs. fault response?
• Verify which limit switch is in series with the close contactor coil (C) during a closing operation. • Confirm whether the open limit switch (LSO) is in the closing circuit or only in the opening circuit. • Confirm that the action you choose would happen every normal closing cycle, not just under abnormal overload conditions.
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