Backfeed on a sub panel to bypass the 120% rule

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Dbarrett

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Reno, NV
I run into this scenario quite often and just want some clarification. I have a 100a service and a 100a ocpd so I can’t backfeed over 20a onto the bus. Question is, can I add a sub panel that is rated 100a and back it with a 50a ocpd and be legal? Usually we just do a panel upgrade but this way is cheaper. Thanks


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GoldDigger

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Placerville, CA, USA
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Retired PV System Designer
Dbarrett said:
I run into this scenario quite often and just want some clarification. I have a 100a service and a 100a ocpd so I can’t backfeed over 20a onto the bus. Question is, can I add a sub panel that is rated 100a and back it with a 50a ocpd and be legal? Usually we just do a panel upgrade but this way is cheaper. Thanks


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The 120% rule applies to each conductor and panel from the point of connection to the inverter back to the main.
You could either do a line side connection or add a second load panel in parallel with the existing panel (grouped so that two main breakers are acceptable as the service disconnect. On the second panel you would use a 50A main. If you move some existing loads into the new panel, you fairly clearly have a case of two main breakers and a load side PV connection.
If the PV is the only thing connected to the new panel, it is indistinguishable from a line side connection. :blink:
 
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