interconnection question [RE-wrenches]

[Darryl Thayer]

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Hello Keith
Yes I believe W. Miller is correct. I ran into this
with the electrial inspectors on my 40+ kW OutBack
system. Here is the way to think about it.  You must
assume that you are at peak, 45 kW, and the roof top
stuff is at zero, and you are back feeding the
distrubution panel with 45kW.  Then a fault current or
high load current occurs, and is there any way that
the fault-load current can exceed the distrubution
panel's busbar rating?  If the main and the roof
supply are both located for example on one end of the
busbar and the  fault-load current occurs  on the
other end the two supplies team up to provide the
current, In your case your main breaker and this
breaker.  In my case the inspectors (6 total) allowed
me to locate my 175 amp 3phase solar breaker at the
far end from the main breaker (220 amp) (250 amp bus
bars) in this case no place on the bus bars can
experiance the sum of the currents. 

--- William Miller <wrmiller at slonet.org> wrote:
> Keith:
> What size load center?  It needs to handle the load
> PLUS the generated 
> power.  This is counter intuitive, but I had this
> explained to me by a 
> licensed electrical engineer and I agreed with the
> concept.  It has 
> something to do with overloading the buss bars on
> the load center with two 
> sources supplying power to the loads.

> Are there harmonics generated by the roof top
> equipment that may mess with 
> the inverters sensing circuitry?
> 
> Do you need to transformer isolate this inverter? 
> If so, would this be 
> more appropriate installed at ground level?
> 
> William Miller
> >If you were looking at putting a 50KW system on a
> building, and were going
> >to use a 45KW Trace unit, and they already had a
> 100 amp, 480 volt feeder on
> >the roof for mechanical equipment, what are the
> specific rules governing the
> >interconnection?

> >My mind says, I will be basically neutralizing the
> load, which is connected
> >to a distribution panel with a 600 amp electrical
> service. But, I know
> >looking at this, it would seem too easy to tie in
> to the panel on the roof,
> >and add a curb for the inverter.
> >Thanks!
> >Keith Cronin



		
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