Maybe when the service drop was pulled down, neutral broke first?
At a place I worked at many years ago, which has many critical computers all over the place, the night cleaning crew used company vacuum cleaners which has twist-lock plugs on them. A few strategically placed outlets were twist-lock type. This was to prevent them from using outlets on circuits with computers. It could also prevent them from operating with plugs half-way pulled out due to pulling the cord as far as it would go.
