It's not only electricity that needs to be isolated and locked out. A lot of machines use air pressure to operate moving parts, so in that case you'd have to isolate all electrical sources as well as the air. The machines I usually mess with require 2 locks. Some of the machines I've seen can require 6 or more locks to be fully locked out and safe to work on.
A typical maintenance period might require 100 or so separate tagouts, each of which could require anywhere from one to dozens of tags. Each duty watch was required to show up early enough to go through the entire tagout book and at least know the gist of what was in progress.
Finding a loose tag was an automatic all hands all work stoppage, until it was tracked down and resolved. No questions, even if your work was in a different compartment, or had no logical connection to what he tag was for.
Each new tagout request had to be signed off on by at least three people, sometimes all the way up to the captain and not just a foreman or supervisor but one or more shop heads.
Seawater system tagouts on a floating sub were serious business.
You're supposed to turn off the circuit breaker and lock it with your own personal lock that only you have the key to. That way no one can turn it on even if they wanted to.
I've heard no one, under any circumstances is allowed to take the lock off. If the person leaves after their shift and forgets to take it off for example, they have to come back in the middle of the night so to speak and take it off.