non-100% rated breakers used in a 1200A MSB - 100% Rated Main

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Trop

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For a 1 MW solar array, I want to centrally combine (29) inverters three phase inverters with maximum current of 39A each.

I have a 1200A main switchboard rated at 100%, per 690.8(B)(1)(a) exception. (29 x 39A = 1,131A at 100%)

Can I put in (29) 50A 3 pole breakers (1,450A of breakers) with each inverter operating at 39A max (x1.25 = 50A OCP with a non-100% rating)?
Or do I have to specify 100% rated 40A breakers in order to use the 1200A main switchboard? This would be 1160A of source current on the breakers.
Thanks.
 

Smart $

Esteemed Member
Location
Ohio
Providing this is going to be an AC-combiner panel only (i.e. no utilization loads), you can use non-100%-rated 50A breakers. However, you may want to get approval by the AHJ prior to installation. Some AHJ's may interpret 690.14(C)(4) as applicable to AC-combiner panels.
 

Smart $

Esteemed Member
Location
Ohio
PS: Don't forget that if this combiner panel feeds into the load side of a utility distribution system, you have to use the value of the first inverter disconnect in the 120% rule.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
PS: Don't forget that if this combiner panel feeds into the load side of a utility distribution system, you have to use the value of the first inverter disconnect in the 120% rule.
Unless the AHJ has adopted the 2014 NEC, which (if I understand correctly from reading another thread) now stipulates that the number(s) to be used is/are the maximum rated current of the inverter(s) multiplied by 1.25.
 

Smart $

Esteemed Member
Location
Ohio
Unless the AHJ has adopted the 2014 NEC, which (if I understand correctly from reading another thread) now stipulates that the number(s) to be used is/are the maximum rated current of the inverter(s) multiplied by 1.25.
His profile location says Tennessee. I believe they're still using 2008 NEC.

But when using 100%-rated breakers, that is one downside of the 2014 edition
 
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