point of connection [RE-wrenches]

David Buckner dbuckner at solaresystems.com
Sat May 3 14:16:35 PDT 2008


Just make sure the house isn't going to pull 175 amps and trip the new main. That wouldn't be fun.

-----Original Message-----
From: Travis Creswell <tcreswell at ozarkenergyservices.com>
Sent: Saturday, May 03, 2008 3:06 PM
To: RE-wrenches at topica.com <RE-wrenches at topica.com>
Subject: RE: point of connection [RE-wrenches]


If we could that then we could just install the inverter breaker on the
opposite end of the main lugs then do a plaque/sticker that said something
like "always leave this breaker in this place".  Right?

Travis Creswell
Ozark Energy Services

-----Original Message-----
From: David Buckner [mailto:dbuckner at solaresystems.com] 
Sent: Saturday, May 03, 2008 1:44 PM
To: RE-wrenches at topica.com
Subject: RE: point of connection [RE-wrenches]


That is an option too.  120% = 240 amps - 175 amp main breaker would
allow for 65 amp input of PV.  Sticklers will say that it's not optimal
because someone will come along in the future and ignore the stickers
and plaques that say something like "Do Not Increase Main Breaker Size -
PV Source Connected..." and they'll do it anyway.

David

  



-----Original Message-----
From: Howie Michaelson [mailto:howie at suncatchervt.com] 
Sent: Saturday, May 03, 2008 2:45 PM
To: RE-wrenches at topica.com
Subject: RE: point of connection [RE-wrenches]


Is it not the case that if it is acceptable to derate the main breaker
on
the house panel, that you could backfeed a higher amount into the panel
(all breakers feeding the buss bar cannot add up to more than 120% of
the
buss bar rating)?

Howie
--
Howie Michaelson
NABCEP Certified Solar PV Installer(tm)

Sun Catcher, LLC
Renewable Energy Systems Sales and Service
VT Solar & Wind Incentive Program Partner
http://www.SunCatcherVT.com
(cell) 802-272-0004
(home) 802-439-6096


On Sat, May 3, 2008 11:22 am, Mark Frye wrote:
>
> NEC 2005
>
> 690.8 Circuit Sizing and Current
>
> (A) Calculation of Maximum Circuit Current. The maximum current for
the
> specific circuit shall be calculated in accordance with 690.8(A)(1)
> through
> (A)(4)....
>
> ....(3) Inverter Output Circuit Current. The maximum current shall be
the
> inverter continuous output current rating.....
>
> (B) Ampacity and Overcurrent Device Ratings. Photovoltaic system
currents
> shall be considered to be continuous.
>
> (1) Sizing of Conductors and Overcurrent Devices. The circuit
conductors
> and
> overcurrent devices shall be sized to carry not less than 125 percent
of
> the
> maximum currents as calculated in 690.8(A)...........
>
> David, the Code is set up to force you to size to the inverter rated
> output,
> not the actual power delivered.
>
> I believe the thinking is that you may only have half the PV installed
now
> so the small breaker would "work", but someone else might add more PV
> later
> without upsizing the conductor and breaker and that would be a
problem.
>
> Mark Frye
> Berkeley Solar Electric Systems
> 271 Vistamont Dr
> Grass Valley CA 95945
> (530) 401-8024
> www.berkeleysolar.com
>
> -----Original Message-----
> From: David Buckner [mailto:dbuckner at solaresystems.com]
> Sent: Saturday, May 03, 2008 6:32 AM
> To: RE-wrenches at topica.com
> Subject: RE: point of connection [RE-wrenches]
>
>
> Wrenches,
> If Larry's line side service connection, even with its closer
proximity,
> becomes costlier than the potential load side connection, could he
feed a
> subpanel with the two 30A PV input breakers, then feed into the house
MDP
> with a 40A breaker from this subpanel?  This would require
calculations of
> DC input and resulting max AC output of the inverters.  If the
inverters
> won't ever be putting out 20A anyway, then the 40A (continuous duty?)
> breaker shouldn't be tripping and code would be met?  I'm asking, not
> telling.  Larry, what is the DC STC input anyway?
>
> David
>
>
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