Some types of problems don’t lend themselves to formulaic repairs and aren’t covered by standard repair procedures.
For example, you’re repairing equipment that “mysteriously” breaks down but don’t actually solve the root cause. Eventually, all those toasted electronics, burned motor windings, spun motor bearings, and unexplained shocks at the water fountain make you think maybe there’s a systemic power quality issue that, if solved, will end the mystery breakdown problem.
You can confirm the existence of power quality issues if you have a power analyzer and are adept at using it and interpreting its results. But then what? Locating the cause(s) is typically outside the expertise of the plant electrician or plant electrical engineer.
So you hire an outside engineering firm. Prepare for this by discussing what information they will need before conducting a site audit. That will start with your facility’s one-line diagram but can get much deeper.