I just got a dual XW6048 grid tie system inspected by the local AHJ. A friend who is also a solar contractor started the install but had vacation plans and needed a stand in for inspection. I was sweating it with fingers crossed but it got signed off.
The issue in question was the battery system's connection in the utility fed AC panel. The 200 amp service entrance is down the driveway on a pole. The 200 amp utility-fed sub panel is in the garage. The inverter system's 100 amp grid-connection breaker is connected at the opposite end of the bussbars from the 200 amp main in the garage utility sub panel. The backed-up load panel is fed from the inverter load output with a 100 amp circuit breaker.
This means that the 200 amp utility-fed sub panel (200 amp bussbar rating) is fed with a 200 amp breaker from the utility and a 100 amp breaker from the XW system. The inspector asked me about this with a raised eyebrow. I told him that the 100 amp back-feed breaker connection is larger than the inverter rating but this is needed to provide pass-through current when the utility is available. If you go by the inverter rating instead of the breaker rating the system still has a rating of 50 amps at 240. However, this system has an array capacity of about 5kw as so is only sized to back feed about 21 amps +/-. He accepted this explanation and said that contractors usually try to convince him that it is okay if the source breakers are at opposite sides of the bussbars.
We talked about how if you go by back-feed breaker size, a back-up system would require a panel rated for at least 300 amps.
A Siemens note on back feed current rating: (Thanks for posting this in another thread solar_dave)
From the note:
The 2008 NEC, Section 690.64(B)(2)states, “The sum of the ampere ratings of overcurrent devices in circuits supplying power to a busbar or conductor shall not exceed 120 percent of the rating of the busbar or connector.”
*Interpretation: Main Breaker + PV Main must be less than or equal to 120% of the busbar rating.
Anyone have any other ideas or experiences with getting a sign-off with this issue?
PS. Another pertinent note from a previous thread:
Here is a link to a note from John Wiles about the "controversy" some inspectors may have regarding NEC code section 690.64(B)(2):