[RE-wrenches] Panelboards in Series - Bus Ratings

[Kienan Maxfield]

Corey,

Here's my interpretation. If anyone can point out where I am in error, I would appreciate it if you could correct me.

I just quickly reviewed 705.12(D)(2) and it appears that neither of your sizing calculations are quite right.

Bear in mind that the maximum current of the inverters is defined to be the inverter rated output * 125% [see NEC 690.8(A)(3)].

In 705.12(D)(2)(3) repeatedly says "125% of the inverter output circuit current" and the only time it mentions an ocpd seems to be in reference to the OCPD between the utility and the busbar. Therefore I would conclude that the answer to your question would be that you would need to base the size of the bus bars off of the sum of the maximum current from all of the inverters (meaning 125% of the rated current).

So if you had 4 sub panels, each having 6 inverters rated at 72.2 A each, your larger combiner panel would have to be...
72.2 * 125% = 90.25 A (max current)
90.25 A * 6 = 541.5 A (max current from each sub panel)
541.5 A * 4 = 2166 A for the larger dedicated combiner main panel.



Does this make sense?

Thanks,
Kienan[https://dl.dropboxusercontent.com/u/8017159/seal.jpg][https://dl.dropboxusercontent.com/u/8017159/WilsonPro.jpg]

Maxfield Solar
maxfieldsolar at hotmail.com<mailto:maxfieldsolar at hotmail.com>
(801) 477-0-SUN (477-0786)
(801) 631-5584 (Cell)

———Original Question ————————

*Scenario*

   - 600A *dedicated PV* subpanel w/ (6) 100A circuit breakers, each
   feeding a 60kW inverter (72.2A rated output)
   - Subpanel is fused at 600A and connects to a larger main
   distribution/combiner panel along with other similarly configured subpanels

*Question*

   - Must the main panelboard be sized based on the combined total of OCPDs
   protecting the subpanels, e.g. 600A + 600A + 600A + 600A = 2400A main panel
   rating?
   - Or can the main panelboard be sized based on the combined total of
   inverter output ratings feeding the panel, e.g. 433.2A + 433.2A + 433.2A +
   433.2A = 1732.8A main panel rating?

--
Corey Shalanski