Jeremy:
Bingo! You have discovered the hard truth of grid tie with battery point
of connection compliance (GTWB POC). Your inverter will through-transfer
up to 60 Amps (A), so to use all of that capability, you should feed it
with 60A. However, you are not allowed to feed the inverter with greater
than 40A dedicated over-current protection (OCPD). The arithmetic is:
Buss rating: 200A
Allowed total buss feed: 200A X 120% = 240A
Main breaker: 200A
Allowed PV feed: 240A-200A= 40A*
If you can downgrade the main breaker to 150A you can back feed up to
90A. The arithmetic then is:
Buss rating: 200A
Allowed total buss feed: 200A X 120% = 240A
Main breaker: 150A
Allowed PV feed: 240A-150A= 90A
Downgrading the main breaker is not easy. Most meter/main/combos (MMCs)
will not allow the downgrade-- there is not a 150A breaker made that is
designed and listed to fit in the 200 A panel. I have contacted various
manufacturers and requested that 200 (MMCs) be made that will readily
accept a 150A main breaker, but large corporations do not seem to care
about the needs of a small part of the market..
I had found a 200 A MMC that I could downgrade the main breaker to 150 A,
but not easily. The fit was not perfect -- I had to modify the hold down
bracket, but it passed inspection. Technically I suppose the MMC was no
longer compliant with the listing once I modified it, but sometimes you
gotta do what you gotta do.
Good Luck.
William Miller
* PS: I believe the 2011 NEC has an exception that applies, but I do not
believe any jurisdictions are using that code. I have convinced my local
building officials to pre-adopt certain future code sections. Maybe you
can make the case to your local inspectors. Meet with them, explain the
limitations of the XW as far as intertie amperage and maybe they will allow
use of a 60A breaker.
Wm
At 04:27 PM 12/30/2012, you wrote:
I'm concerned that the inspector will not allow a 60A back fed breaker in
the 200A main panel as it exceeds the 120% rule
Jeremy
Sent via BlackBerry. Sorry for typos and shorthand!
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