Re: [RE-wrenches] Conductor Sizing for Supply Side Connection

Sat, 09 Mar 2013 07:19:51 -0800

Had a couple of minutes here, so with the load side connection, the 200 amp breaker would operate to protect all conductors. With a supply side connection, the battery charger could be pulling 60 amps, the main panel 200, and the service conductors sized for 240 amps would fail. 2/0 in free air is rated for 265A T310.15(B)(17), but would you say that T310.(B)(16) applies for service conductors and then 2/0 is 175? 

I am really starting to hate solar.
On 2/28/2013 10:21 AM, Dave Click wrote:
As a note, supply side connections have an extra complication with battery backup systems. With a regular GT inverter you're just pushing current into that interconnection point and you can work out easily that you won't have any overcurrent issues unless you made a big mistake and your inverter output exceeds the rating of your service conductors. However, with a battery system you're also potentially pulling current from that point. Before the battery inverter is installed your main breaker protects your service conductors, but if the inverter is pulling in 60A and the main breaker is also operating near its capacity, you could have >240A running over 200A service conductors with no breakers tripping. You would overwhelm the capacity of the service [230.23(A)] and no breakers would trip. You could fix this by replacing your service conductors back to the transformer (I'm just saying that it's an option) or downsizing the main breaker, and at that point you're probably better off just making it a load side connection. I'd go load side and argue with the AHJ to use the 2011 update mentioned earlier. 

Dave

On 2013/2/28 9:55, Garrison Riegel wrote:


Allen,


The benefit I see would be to allow for a code compliant load side 
connection on a 200A panel with a 200A MB, where the AHJ is on the 
2008 NEC or older and will not listen to your good logic.  I don't 
think this would always be the best option, but if backup loads and 
inverter output were less than 32A then a 40A OCPD in the main panel 
should be fine?  Since it sounds like the 60A breaker in the main 
panel is not a safety issue, but a design consideration, I suppose I 
would just prefer flexibility when possible.



That said, this AHJ is on the 2008, and the loads will be less than 
30A, but based on this conversation I plan to go with a 60A and try 
to convince the AHJ that it will be code compliant in their future!


Thanks,

Garrison


*From:*re-wrenches-boun...@lists.re-wrenches.org 
[mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of 
*Allan Sindelar

*Sent:* Thursday, February 28, 2013 8:14 AM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Conductor Sizing for Supply Side Connection

Garrison,

I don't know why it's not listed as 60A max, but my own internal 
logic would ask why it should be. The only benefit I could see for 
using smaller than a 60A breaker would be to allow use of #8 
conductors (allowed with a 40A or 50A breaker) instead of the #6 
necessary with a 60A breaker. And of course, you could use a 40A 
breaker with #6 conductors, so theoretically it would be fine. I just 
fail to see any benefit to doing so.

Allan

*Allan Sindelar*
al...@positiveenergysolar.com <mailto:al...@positiveenergysolar.com>
NABCEP Certified Photovoltaic Installer
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder and Chief Technology Officer
*Positive Energy, Inc.*
3209 Richards Lane (note new address)
Santa Fe, New Mexico 87507
*505 424-1112*
www.positiveenergysolar.com <http://www.positiveenergysolar.com/>

On 2/28/2013 6:27 AM, Garrison Riegel wrote:

    Thanks Allen for clarifying why a 60A is required.  I was
    wondering.  The spec does list a surge current of 9000W so I
    thought that may be the rationale, but even that would only
    require a 50A, and since this surge occurs during 'stand-alone

    mode' it didn't seem to apply to the OCPD at the main panel. 
    Your explanation makes more sense, but I wonder why then they

    don't list the AC input breaker size as 60A /max/.  If you have
    few backup loads, and are not on the 2011 NEC, a 40A could
    theoretically be fine?

    Thanks all for your thoughts, much appreciated.

    Garrison

    *From:*re-wrenches-boun...@lists.re-wrenches.org
    <mailto:re-wrenches-boun...@lists.re-wrenches.org>
    [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of
    *Allan Sindelar
    *Sent:* Wednesday, February 27, 2013 6:08 PM
    *To:* RE-wrenches
    *Subject:* Re: [RE-wrenches] Conductor Sizing for Supply Side
    Connection

    August,
    The 60A breaker is intended to allow grid power to pass through
    to the loads in excess of the inverter's stand-alone output. The
    point of 705.12 (moved in the 2011 NEC from 690.64 (B)(2)) is to
    differentiate between load pass-through current and sell current.
    The amount of current fed into the grid is (4500/230 =) 19.56A,
    while the amount that can be taken from the grid and passed
    through to the load is much greater. If you were limited to a 40A
    breaker in order to maintain 120% of a 200A main bus, you'd be
    prone to nuisance trips under large cumulative loads.

    Allan

    *Allan Sindelar*
    al...@positiveenergysolar.com <mailto:al...@positiveenergysolar.com>
    NABCEP Certified Photovoltaic Installer
    NABCEP Certified Technical Sales Professional
    New Mexico EE98J Journeyman Electrician
    Founder and Chief Technology Officer
    *Positive Energy, Inc.*
    3209 Richards Lane (note new address)
    Santa Fe, New Mexico 87507
    *505 424-1112*
    www.positiveenergysolar.com <http://www.positiveenergysolar.com/>


          





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