Your plant has been using the same electrical testing firm for many years. One task that the firm handles for you is cable testing. They've always been good at getting in and out, never causing a shutdown to run past schedule — and that includes replacing cables as needed. This year, however, their project manager told you there were too many cables to replace within the allotted time. He suggested scheduling another shutdown just for that purpose as soon as planning and staffing could permit.
What do you tell your boss?
You'll have to explain to production supervisors, the plant manager, and possibly the division VP why "this time" you need an additional shutdown. They won’t like it, and they'll ask what you're doing to prevent a recurrence.
To develop the solution, you must determine the cause. Most likely, it was a transient event. If you have a robust power monitoring system, you can probably determine what, and when, that event occurred. Thus armed, you can develop the most effective remedies for preventing a recurrence. For example, if a transient occurred coincident to starting your fire pump motor across the line, then you'd look into a soft start for that motor. If you don't have power monitoring, this expensive problem helps justify installing a system that monitors down to the feeder level.