Question: 

When securing equipment for safe maintenance, special tags are attached with the lock(s) used to keep circuit breakers and other disconnect devices in the open (off) state. A typical "lockout" tag looks something like this:

What is the purpose of attaching such a tag to an electrical disconnect device in addition to locking it in the open position? Why is a lock, by itself, not sufficient from a safety perspective?

Answer: 

A tag informs anyone wishing to turn the disconnect device "on" as to when it was turned off, and who placed the lock(s) on it. Many lockout tags have space on for a written description so that the reason for the lockout may be explained.