Additional PV system to connect. NEC 705.12(a)

A

Andres Arias

PV Solar engineer
Location
New York
Occupation
Electrical Engineer
Hello dear colleagues.

I have a main electrical panel with a PV string inverter system (OCPD: 25A) connected with line taps in the feeders. An additional PV system based on microinverters (OCPD: 30A located in an AC combiner) will be installed in the same electrical panel of the house. Is it correct to install this new sytem using line taps in the supply side of the electrical panel, given that there is another connection with line taps?. FYI, the main panel busbar rating is 100A and the main breaker is 100A as well, so the NEC705.12A is met:

OCPD(micros) + OCPD(string inverter) < busbar rating

(30 + 25) < 100 --> 55 < 100 then OK

Let me know your thoughts. Thank you
 
If I understand you correctly, the original PV system was done with a line side tap because it would not meet the "120% rule" to land a breaker in the panel. That is only more true if you are adding PV. I would probably be looking to redo the line side tap so it can be distributed to both the old and new PV systems, if the wires aren't already rated for 55A or more. A second tap would be allowed on paper but may or may not be a good idea depending on details.
 
jaggedben said:
If I understand you correctly, the original PV system was done with a line side tap because it would not meet the "120% rule" to land a breaker in the panel. That is only more true if you are adding PV. I would probably be looking to redo the line side tap so it can be distributed to both the old and new PV systems, if the wires aren't already rated for 55A or more. A second tap would be allowed on paper but may or may not be a good idea depending on details.
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If the additional PV system Imax would fit into the MDP under 705.12 is there any reason why he couldn't add it there?
 
jaggedben said:
Well, it wouldn't if the OCPD is sized appropriately and it needs to meet the 120% rule. Perhaps there's another way, but more detail would be needed.
Click to expand...
Sorry, I did not read the OP closely enough. Apparently 125% of the additional PV is or is close to 30A and the panel is 100A/100A, so no, it would not fit in the existing panel. 125% of the additional system Imax would have to be 20A or less. My bad.

I would combine all the PV and adjust the OCPD and wire sizing to the tap accordingly.

Sometimes a customer would tell us that they intended to add more PV and/or a BESS later; when that happened we encouraged them to build expandability into the initial installation to save them time and money in phase 2 of their system.
 
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