I believe you are using the word ?emergency? in a way that is different than the NEC uses that word. So for a moment, let us drop that word from the discussion, and talk only about locally owned and operated generators.
If you are asking if a business can buy their own generator, and use it for their one and only power source, thus not obtaining any power from the local utility company, the NEC has nothing to say about that. If you mean that there is an existing utility connection to one building, and the owner is constructing a second building, and the owner wants to power the new building from their own generator (and not from the existing building), the NEC has nothing to say about that.
On the other hand, if the equipment that the owner intends to power from the generator is located in a building that already has a power source from the utility, and if that equipment does not fit into the classification of ?emergency,? as that word is used by the NEC, then there might be an issue.
Now back to the word, ?emergency.? It is possible that the building under discussion has loads that meet that definition. Egress lighting is one common example. If the owner plans to power their non-emergency equipment and the required emergency lights from the same, single power source, with no option for getting power from a second place (i.e., if the generator were to trip), then the NEC would not allow that situation to exist.
Can you give us more information about the situation?
