We have a big service on our generator system ( 8 Gen sets and each is 2.5MW). A portable generator has been deployed to replace each when it is under maintenance and it will take one month for one generator. My question is, do we have to provide a temp. warning label based on this kind of operation? Since the portable gen set is smaller than the servicing one, we have to adjust some relay setting in order to achieve max. coordination of downstream devices. And code or standards say a temp label is required?

I don't know the Canadian standards but regardless, I think you should be asking what is the safest action to take to protect the employees? Looked at that way, I would think you would want to label the temp genset.

I agree with wbd. The issue for me would be, does anyone need to work on the equipment during this temporary installation and if yes then it should be labeled. During an emergency, is not the time to wonder what the arc flash rating is. Also if the installation has stickers now and the temp situation is a different arc flash hazard, how will that be communicated.

No, you don't HAVE to do this. You can simply use the tables in 70E to determine your arc flash levels and use that more conservative number. Of course you still have to figure out short circuit current, breaker trip times, etc., so effectively you might as well do the real thing. Updating a power system analysis takes about 15 minutes to gather data and 15 minutes to work with the software. I work in a surface mine. The mine moves at an advance rate of about an acre a day. Every 3-6 months, every substation gets disconnected, moved, and reconnected. So we continuously change the model.