Does anyone ever use two arc flash labels on the same piece of equipment based on operating conditions? We have a MCC section that can be fed from an emergency generator. When on the generator it is a HRC 3 due to clearing time, but when it is on the power company it is a HRC 1. I feel two labels violates the "keep it simple' principle which is often expressed here and I actually agree with; however, typically our generator runs feeding this MCC for one 16 hour period every two years - literally. I hate to force the electricians into Cat. 3 on all those occasions when it is not needed. It is obvious to the electricians when this MCC is being served by the generator. I realize the equipment must be labeled for the worst case condition, but I have not seen it said that the equipment cannot be label for both operating conditions.

We have customers that created special labels that have both conditions on a single label.
We have customers that have put normal operating condition labels on and do not allow work 'when on generator supply'.
We have customers that label the worst condition, and then have a safe work practice program (standard work permit) that allows them to use the lower value when the generator is not running.

I agree with JBD. I have seen it done all ways. When I have a project that has a EDG associated with it, I always ask what the company policy is. Some facilities do not allow any work when on emergency power. I will always include in the report the AFH with the EDG operating.