Article 690 Photovoltaic Systems

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nrgocba

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We are responsbile for the AC side of this PV installation. From ( 2 ) 100KW inverters we are providing overcurrent protection at 150A ea. from ( 1 ) 300A MLO load center on roof which is being fed to MSB. We are providing a 300A overcurrent device at main switch board. We sized our conductors at 125% of output rating of inverters. We determined conductor size to be ( 350 MCM Cu). This is a 480V, 3 phase system. Is this correct ? We are being instructed by the electrical inspector to refer to NEC article 705.12 D2. Inspector is stating that we need to add the sum of all over current devices and rate our buss bars and conductors at 600A instead of the 300A that we calculated. Please advise.
 

Smart $

Esteemed Member
We are responsbile for the AC side of this PV installation. From ( 2 ) 100KW inverters we are providing overcurrent protection at 150A ea. from ( 1 ) 300A MLO load center on roof which is being fed to MSB. We are providing a 300A overcurrent device at main switch board. We sized our conductors at 125% of output rating of inverters. We determined conductor size to be ( 350 MCM Cu). This is a 480V, 3 phase system. Is this correct ? We are being instructed by the electrical inspector to refer to NEC article 705.12 D2. Inspector is stating that we need to add the sum of all over current devices and rate our buss bars and conductors at 600A instead of the 300A that we calculated. Please advise.
Not enough info. Need to know the max current rating of the MSB and the rating of all ocpd supplying power to it (your 300A ocpd is but one).
 

bluesmoke...oops

Senior Member
The PV system is a source as is your feed from your utility. You have to account for the possibility that both those sources can supply your system at the same time.
 

ty

Senior Member
It seems like you (your inspector) is talking about 2 different things.
The wiring from your inverters to the mcb and their ocpd is not the same thing as the mcb buss bar rating.
Your pv array breaker(and therefore pv system size) in the mcb cannot be more than 125% of the buss rating.
 

megavolt

Member
It seems like you (your inspector) is talking about 2 different things.
The wiring from your inverters to the mcb and their ocpd is not the same thing as the mcb buss bar rating.
Your pv array breaker(and therefore pv system size) in the mcb cannot be more than 125% of the buss rating.
Ty,
See 690.64(B)(2). The allowable percentage is 120.
 

bluesmoke...oops

Senior Member
It seems like you (your inspector) is talking about 2 different things.
The wiring from your inverters to the mcb and their ocpd is not the same thing as the mcb buss bar rating.
Your pv array breaker(and therefore pv system size) in the mcb cannot be more than 125% of the buss rating.
690.64(B)(2) also says that the sum of your overcurrent devices providing power
to the bus can't exceed 120% of the bus rating. I read that to mean that to mean that if you supply the bus with a 300A C/B from the main, and 2 150A C/B from the PV array, you have to have a 500A bus rating minimum in the panel all this connects to.
 

ty

Senior Member
I am really sick, and highly medicated. With that in mind, I think I agree with you.
 
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