[RE-wrenches] Conductor Sizing for Supply Side Connection

Fri Mar 1 06:40:30 PST 2013

Gary,

I thought most inverters share power. So if the inverter has a 60A transfer
switch and all of that is needed for loads then none for charging and as
load demand decreases, charging increases.

Larry Liesner
Elektron Solar
On Feb 28, 2013 11:33 AM, <gary at icarussolarservices.com> wrote:

> Garrison, et al:
>
>
>
> Another consideration when sizing the POCC OCPD (either load side or
> supply side) is charging current when the grid power returns and the
> battery bank is near the LBCO voltage.
>
>
>
> Bulk charging current and AC pass-through current both must be considered
> when sizing the POCC OCPD.
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> Regards,
>
>
>
> Gary Willett
>
> Icarus Solar
>
> On Thu, 28 Feb 2013 10:04:51 -0600, Garrison Riegel <
> garrison at solarserviceinc.com> wrote:
>
>  Great point Dave.  It crossed my mind that it was technically possible,
> but figured since I would be removing loads off the main panel it was
> highly unlikely.  Thanks for the code reference.  I’ll go load side, and be
> prepared for some discussion.
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> Thanks,
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> Garrison
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> *From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
> re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *Dave Click
> *Sent:* Thursday, February 28, 2013 9:21 AM
> *To:* re-wrenches at lists.re-wrenches.org
> *Subject:* Re: [RE-wrenches] Conductor Sizing for Supply Side Connection
>
>
>
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> 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:
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> Allen,
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> 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.
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> 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!
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> Thanks,
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> Garrison
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> *From:* re-wrenches-bounces at lists.re-wrenches.org [
> mailto:re-wrenches-bounces at lists.re-wrenches.org<re-wrenches-bounces at 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*
> Allan at 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
>
>
>
>
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> 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?
>
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> Thanks all for your thoughts, much appreciated.
>
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> Garrison
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> *From:* re-wrenches-bounces at lists.re-wrenches.org [
> mailto:re-wrenches-bounces at lists.re-wrenches.org<re-wrenches-bounces at 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*
> Allan at 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
>
>
>
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