120% of bus rating allowed?

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winslowfam

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Hi...we have a client who is adding a solar power supply to an existing 480 volt panel that will be in addition to the original utility connection. They plan to connect the output of the solar power inverter to the panel via a spare feeder breaker rated appropriately. Our concern is that this could lead to overloading of the panel main bus by adding this power source to the main bus in addition to the normal utility connection supply. The normal utility source is rated at the bus amp rating, so adding another source could lead to overload of the bus. We have been told that the 2008 NEC allows for overloading of a panel main bus by 120% in some cases. Anyone hear of this before and can you direct me where to look in the NEC?
 
winslowfam said:
Hi...we have a client who is adding a solar power supply to an existing 480 volt panel that will be in addition to the original utility connection. They plan to connect the output of the solar power inverter to the panel via a spare feeder breaker rated appropriately. Our concern is that this could lead to overloading of the panel main bus by adding this power source to the main bus in addition to the normal utility connection supply. The normal utility source is rated at the bus amp rating, so adding another source could lead to overload of the bus. We have been told that the 2008 NEC allows for overloading of a panel main bus by 120% in some cases. Anyone hear of this before and can you direct me where to look in the NEC?
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See 690.64(B)(2) in the '08.
 
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