If your service goes down, its likely because of an unplanned outage. Could be anything from someone hitting a pole and brining everyone offline or a blown fuse in the plant or loss of commercial power. Loss of commercial power would result on the inverter in the power supply resorting to backup power and immediately a line tech is dispatched to see what happened and plug the node into their bucket truck's inverter to keep everything online. If it goes down during the maintenance hours which is in the middle of the night, its likely due to a planned outage as those times have the least customer impact.
Service can go down in the middle of the day for a few minutes if someone is doing a quick "break plant" to fix something on a run that doesn't have that many customers or a quick fix on a fix that needs fixing asap.