So while your all here on the safety topic, what do you all do when adding a say a 30A branch to a 480V panel?
We'll stick with a 1980's era panel with no labeling for this example.
Say your doing a new breaker, new wire pull into the panel etc.
De-energize the entire panel?
Energize Electrical Work Permit to the boss? (what if your a one man show the owner of the building?)
PPE space suit?
Hire a company to do a safety risk assessment and make a AF label?
We would have the panel shutdown for the conduit entry, breaker installation, and conductor termination.
We would also have the load end finished, the wire pulled to a pull point close to the panel, and the conduit to enter the panel prefabbed before the panel is shut down to limit the down time.
However that does not really answer the question of how you can verify the absence of voltage as you would need PPE suitable for the hazard, and with no markings you have no idea what the PPE may be. You could make some guesses based on what information you have, but that is not the best idea.
For new project, I specify the Panduit VeriSafe Absence of Voltage Tester. This is permanently installed and lets you prove absence of voltage without removing a cover. I think once there is a couple of more devices like this are on the market the code will start to require such devices. As far a I know the Panduit one is the only one on the market that OSHA says you can use for this purpose, and it is difficult to include a code rue that requires a product that is only available from one manufacturer.