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

[Jason Szumlanski]

We have avoided any load side code issues by doing supply side taps on
older buildings. The AHJ typically turns a blind eye to the load side
issues if we use this interconnection method. That is not to say that
you shouldn't strongly encourage the owner to address the load side
deficiencies or code violations, if any. Nonetheless, adding solar to
the supply side of the main disconnect would not exacerbate any existing
problems on the load side. 

 

Jason Szumlanski

Fafco Solar

 

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of JRQ
Sent: Friday, December 23, 2011 3:51 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Landing into a sub-panel without a main
servicepanel, just a main switch

 

Yes, if there is a distribution block and several subpanels are fed from
the same point downline from the main disconnect, then what I'm
describing would not be applicable. The other subpanels function as
loads with respect to the distribution block. The same if there are any
taps on the load side of the main disconnect. 

 

We need to see a wiring diagram for how these subpanels are connected
together to give a definitive answer.

 

Jeffrey Quackenbush.

 

________________________________

From: Richard L Ratico <Richard.L.Ratico at VALLEY.NET>
To: re-wrenches at lists.re-wrenches.org 
Sent: Friday, December 23, 2011 9:43 AM
Subject: Re: [RE-wrenches] Landing into a sub-panel without a main
service panel, just a main switch

Jeffrey,

On the load side of the Fused 200 Amp Service Disconnect there is a
splice or
splices or distribution block in the conductors which feed the 5
subpanels.  It
seems quite possible that one or more of those conductors or the
distribution
block could see the sum of the current from the grid and the current
from the
solar. A combination of loads in the 4 subpanels, other than the one
backfed by
the solar breaker, could overload the conductor or part of that
conductor
carrying that combined current, without necessarily blowing a main fuse
or any
of the breakers. The devil is in the details, in this case the size of
the
conductors and the way they are utilized.

Ray has a point. It is possible there are existing code violations.
These should
be corrected in a manner which facilitates inclusion of the solar.

Dick Ratico
Solarwind Electric

--- You wrote:
The flow of electricity isn't two-way traffic along a conductor. If
there are no
loads on the conductor between the main system disconnect and the main
breaker
of a subpanel, in this scenario, there can only be up to 200 A coming
from the
utility OR up to 60 A coming from the solar system backfed through the
subpanel.
The intent of limiting the solar system size plus the utility source to
120%, or
even 100%, of a bus or conductor rating is when that bus or conductor
can
potentially see current from both sources simultaneously, it could
overheat if
these sources exceed the bus or conductor rating. That's not physically
possible
unless there is a load in between both sources. 
--- end of quote ---
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