Generator Sizing???

[Todd C]

We're going to buy and have installed, a generator on our County Courthouse. We will hire a contractor. I just have to be able to oversee the project, and assure the Commissioners we're getting the right thing, and not paying too much. There will be load prioritization. I'm just starting to identify the circuits that we need to carry in an emergency. Then I'll have to size the generator and choose a system. I'm going to leave my questions very general for now. Can you get me steered in the general direction I should be thinking? My 2002 NEC is a bit out of date. Any game changing new rules I need to be apprised of? I still have to meet with our Emergency Management Coordinator. He's going to want to bring in some communications systems to consider I suppose. What do I need to know, or to have figured out, before I make a purchase, hire a contractor, or even just to pitch the project to the Commissioner's Court?

 

[iwire]

In my mind first off you need to determine if this generator will be supplying emergency loads (see NEC article 700) or optional standby loads ( see article 702) or both.

The rules are much stricter for article 700 loads.

How big are you thinking?

Start getting too big and there can be EPA issues to consider.

 

[charlie b]

The first question I would ask in such a situation, and I mean ask of whoever constitutes ?the owner,? is this: If the utility company?s power source were to fail, what do you want your people (i.e., the building?s occupants) to do? Among the choices are, (1) Have everyone continue working as if nothing had changed, (2) Have a select few people in critical roles continue working, and let the remainder of the people leave (either to work from home, work from a different location, or not work at all) until the utility power is restored, and (3) Have everyone shutdown all the computers and other equipment, lock up anything that needs to be locked up, and quietly leave the building until further notice. The answer will depend on the information available from the utility company, regarding the likely amount of time before power is restored.

The building codes will require that a path of egress be illuminated for a minimum of 90 minutes, so as to allow the occupants to safely leave the building. You don?t need a generator to perform that function, as battery-backed light fixtures can do this job. But if you intend to use the generator to perform this function, then that part of the generator?s distribution system falls under the rules of ?emergency power,? as described in article 700. The computers and other equipment that the owner would want the people to continue to use during a utility outage would fall under the rules of ?optional standby power,? as described in article 702. The two systems cannot share the same transfer switch, conduits, junction boxes, or other portions of their respective distribution systems (with a few minor exceptions that are outlined in article 700).