Whilst unloading a sand cargo, black smoke was seen pouring from the side panel/electrical box of the ships discharge excavator. The operator was alerted and attempted to turn off the machine by key but it failed to switch off. An attempt was made to open the side panel of the excavator.  Once the black smoke had cleared no flames were identified but significant charring/melting was seen on the main electrical panel. Around 2 minutes later the engine cut out on the excavator and all electrical power to the cab was lost.  Please see incident alert for further information.