While Zog's suggestion is clearly the superrior one you can use the tables in NFPA 70E 130.7 to determine Hazard Category in lieu of an incident energy study. You have to be careful though as there may be areas with low impedance transformers, etc that give you a higher normal than fault current/energy. Best to have a study as it can also possibly eliminate unnecessarily bulky PPE.
The best thing to do is to hire someone to do the study. Having a study done has many benefits:
... expected that the amount of effort that will generate will keep them bust indefinitely.
my understanding is they have labeled about 1/3 of the stuff in the plant they plan to label.
A good company can come in collect data, creat a report , and install labels for 1000+ locations, start to finish including job take off, quotation, review meetings, and indecisions in less than 6 months.
There is absolutely no reason to evaluate things that have not changed. After all, if the equipment has not physically changed, the model is still valid.
Keep the model up to date and relable the locations that have changed since last time.