2017 NEC 705.12 (B)

[lukejm]

If a load side connection is made in a remote sub panel and the bus ampacity is sufficient to dissipate the load, and the connection is made at the opposite end of the panel, do all the panels on the premises need to meet the 120% rule or just the point of connection. Thank you!

 

[jaggedben]

All panelboards connected in series between the point of connection and the service need to meet one of the rules in 705.12(B). The 120% rule is one of the options, not all panelboards involved need to use the same rule.

 

[lukejm]

Thank you for the reply. Have you had a chance to read the 2020 NEC on this? It states that the "interconnecting equipment has to meet 705.12 (a) thru (e)". That is why I am asking the question. To me that changes everything. Am I wrong?

 

[jaggedben]

Yes, you're kind of wrong, because really the only changes were re-numbering the sections, not so much changing the requirements. What was 705.12(A) became 705.11, and what was 705.12(B) became just 705.12.

Regarding your original question, the relevant rules have not changed since the 2014 NEC. There used to be a section in the 2011 NEC about which breakers to use for calculations when panels are connected in series, but that was removed in the 2014 because they no longer used breaker ratings but rather 125% of inverter output.

 

[jaggedben]

All panelboards connected in series between the point of connection and the service need to meet one of the rules in 705.12(B). The 120% rule is one of the options, not all panelboards involved need to use the same rule.

In this post I should have specified 705.12(B)(2)(3) for 2017. The 2020 equivalent is 705.12(B)(3).