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#19306 - 12/24/02 02:48 AM One more generator question??
sparkync Offline

Registered: 10/17/02
Posts: 811
Loc: NC
Anyone see anything wrong with putting bigger load in a generator panel than the generator is capable of carrying,(as long as the individual circuits are protected and the inter-locks are in place for the mains, and the panel is rated for the combined load, etc....etc.....)so that the individual loads can be turned on and off as needed??? For example....say you've got your well pump on and a few lights and receptacles, and you want to heat your water up, so you turn your lights or whatever off, and turn your water heater on... Am I missing something in the code.. Seems like this should be OK since, if the generator gets overloaded, it will shut down anyway??? Thanks again for the input..I want to make sure I got everything right..I've got a couple of these jobs coming up......... Steve

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#19307 - 12/24/02 03:41 AM Re: One more generator question??
sparky Offline

Registered: 10/18/00
Posts: 5545
In my experience, it's a good idea to have the customer participate in sizing the critical loads.

Trying to keep it simple , i usually ask that they add up this in wattage x 1.25%

However, when they realize the $$$ involved in higher KW genny's the issue of 'juggling always arises.

There are many undesized genny's that have an all inclusive auto-T switch , simply surviving on a crap shoot re; loads on @ time of transfere.

This, as opposed to the Gen-Tran 20216 or similar models that require manual intervention probably buys one little 'code' slack, yet makes 'juggling' loads a practical option.

#19308 - 12/28/02 06:11 PM Re: One more generator question??
Trumpy Offline


Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Do you guys, not have Maximum Demand Calculations, in the US?.
These give the fact,(called Diversity Factor),that not all of the loads will be drawing current at the same time.
We use these calcs, to size Mains and Sub-Mains, over here in New Zealand.
These Calcs, can also be applied to Gen-Sets
too, as they are the same as a Mains supply.
Let's face it, these days if you're not young, you're old - Red Green grin

#19309 - 12/29/02 12:10 AM Re: One more generator question??
nesparky Offline

Registered: 06/21/01
Posts: 650
Loc: omaha,ne
The power companies use a derating factor from the calculated load of a building. This allows them to use smaller service wire than the calculated load would require if wired by the NEC. They know that electrical usage is not what the calculated load is. Different occupancies have different derating factors depending on simular loads served and thier usage history.
Check with the local utility and the AHJ before sizing the generator. Also find out from your customer what he really wants from the generator. You may be suprised how small the required generator will be. Of course if the customer has plans to add load later that should be addressed.
Good luck


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