[RE-wrenches] Landing into a sub-panel without a main service panel, just a main switch

[Ray Walters]

I'd consider a fused disconnect on the line side of the 200 amp main.  
The wires on the load side are treated just as a bussbar. 690.64 (which 
is now 705.12) reads conductor or bussbar.
You could use a 100% duty rated 40 amp fused disconnect, and get up to 
9600 watts through on the load side, but a regular disconnect is going 
to be limited by 690.8 to 80% of 40 amps, (7.7 KW inverter rated output 
x 125% = 40 amps)
Since the subpanels have 125 A bussbars, but only 60 amp mains, you 
could add there without further penalty, but the bottom line is: you're 
not going to get 10KW on the load side and be code compliant.

Ray Walters

On 12/22/2011 11:34 AM, Pekka Laine wrote:
> All,
>
> We have been contracted to install a 10kW-ac system into a 45-year old house that has no main service breaker panel, only a 200A fused main switch (Zinsco). There are five 125 A rated sub-panels throughout the house, some of which have 50A&  60A breakers in them.  I have been told that we are not limited to 40 A max. PV as per 690.64 (B) since there is no main bussbar. I have three questions:
> 1. Can we land 60A into one of these existing sub-panels
> 2. If not, how would you recommend "tapping" in the old 200 A fused main switch wires?
> 3. What do you think is the maximum amperage of PV that can be backfed in to this service?
>
> Any other recommendations welcome.
>
> Respectfully,
>
> Pekka Laine
>
> President
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