Does 2014 NEC 705.12(D)(2)(3) apply for line side directly tap (no PV breaker)

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fandi

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Electrical Engineer
Hello All,
My co-worker showed me his PV design like this:
The current goes out from a 300A AC output inverter to a 400AS/300AF fusible disconnect and then tap directly to the supply side of the main 600A breaker of a 600A main switchboard fed from POCO. The fusible disconnect is installed side by side with the 600A switchboard.
My argument is the switchboard is now overloaded 600A + 300A = 900A. So is a backfed PV breaker required and does 2014 NEC 705.12(D)(2)(3) apply in this case?
Thanks.
 
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Since the tap is between the meter and the main breaker, there is no place in the main panel that is even potentially subject to the sum of the two currents.
And on the service conductors there are no other load which would otherwise be protected by the 600A breaker.
On the service conductors the PV backfeed current will always be out of phase with any local load current, so the service wires will never see more than their 600A rating.
In those cases the NEC only requires that the PV backfeed be no larger than the size of the service.
 
GoldDigger said:
Since the tap is between the meter and the main breaker, there is no place in the main panel that is even potentially subject to the sum of the two currents.
And on the service conductors there are no other load which would otherwise be protected by the 600A breaker.
On the service conductors the PV backfeed current will always be out of phase with any local load current, so the service wires will never see more than their 600A rating.
In those cases the NEC only requires that the PV backfeed be no larger than the size of the service.
Click to expand...
So I guess no PV breaker nor the code section mentioned above is required. Thank you sir.
 
fandi said:
So I guess no PV breaker nor the code section mentioned above is required. Thank you sir.
Click to expand...

You still need a "PV breaker" to serve as a PV disconnect and to protect the service wires from short circuit or ground fault.
In this case, however, the disconnect and OCPD are in the form of a fused disconnect. The Code rarely requires that OCPD be a breaker.
 
fandi said:
So I guess no PV breaker nor the code section mentioned above is required. Thank you sir.
Click to expand...
The connection described falls under 705.12(A). Note the general statement of 705.12 requires compliance with (A), (B), (C), or (D).
 
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