[RE-wrenches] Gray code area

[Drake Chamberlin]

Kent and Jerry,

Thanks for the ideas.  The idea of a label is a good one.  Since the 
building in which the box is located is fed by a completely separate 
service, no loads should ever be tapped from it. The inspector should 
be contacted first, since this method is not completely in line with 
the code rules.

The breaker cannot really be down sized, since it feeds the 
residence.  The solar feed would be about 46 amps, or about 23% of 
the rating of the mains.  Can we use adjustable trip breakers to meet 
the 20% requirement?  If we use them, do we need certification 
concerning their amperage capacity?

The problem with more spaces being available on the bus bar might be 
addressed by altering the bar.  But, I'm guessing that this would 
void its listing.

Drake


At 03:45 PM 7/27/2008, you wrote:
>Drake,
>
>I agree that taking it up with your inspector ahead of time is a 
>good idea, but it is possible he may not accept the argument that 
>the panel isn't for loads if there are additional spaces for 
>breakers that someone could use later on.
>
>How much inverter capacity (amps) are you connecting to the panel?  Is
>it possible to change out the breaker for a smaller one or de-tune 
>the trip setting of the breaker to
>bring you in compliance with the sum of breakers rule?
>
>
>Cheers,
>
>Jerry Caldwell
>
>Recurrent Energy
>
>
>
>----- Original Message ----
>From: Kent Osterberg <kent at coveoregon.com>
>To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
>Sent: Sunday, July 27, 2008 7:49:11 AM
>Subject: Re: [RE-wrenches] Gray code area
>
>Drake,
>
>The writer's of section 690 haven't covered all of the possible ways to
>make a safe installation.  Or all of the needs for a large system.  You
>should take it up with the AHJ first, but I suspect that it will be
>approved.  After all, the 20% rule (and now with NEC 2008 at the bottom
>of the bus too) was intended to prevent overload of the bus bars.  The
>20% rule shouldn't apply if there aren't any loads in the panel.
>
>Consider this possibility: you have six 3-kW inverters to install on
>this 200-amp panel.  Do you have six points of interconnection with the
>utility on the bus bars?  Or do you have one point of interconnection at
>the line side of the 200-amp breaker?  I think it is really the second
>and I think that is what the electrical contractor was thinking. You may
>need to label the panel to make it clear that it isn't for loads.
>
>Kent Osterberg
>Blue Mountain Solar
>www.bluemountainsolar.com
>
>
>Drake Chamberlin wrote:
> > We are installing a PV system where an electrical contractor left us an
> > easy way to interface with the grid.  The contractor does extremely
> > clean work which exceeds NEC requirements, and the local code
> > authorities are very happy with him.
> >
> > What he left us was a 200 A, feed through breaker box that feeds no
> > branch circuits.  The building that the breaker box is in is fed by a
> > separate, commercial service.  The feeder on the feed through lugs, from
> > the box, goes to a residence where the wiring feeds a 200 A service
> > disconnect breaker for a residential electrical service.
> >
> > The sole purpose of the breaker box is to give us a place for the PV
> > input.  The potential code issue is that the PV input goes over the 20%
> > limit.  But there is no way the bus can be overloaded, since it is
> > protected by a 200 A breaker on the load side.  Since the building is
> > commercial, and fed by a separate service, there would be no reason to
> > tap any loads from the box in question.
> >
> > This doesn't look code compliant, from the wording of the NEC.  Do you
> > think we should use the bus bar and backfeed a breaker, or tap in ahead
> > of the 200 A breaker to strictly meet code requirements.
> >
> >
> >
> > Drake Chamberlin
> > Athens Electric
> > OH License 44810
> > CO License 3773
> > 740-448-7328
> > 303-328-5533
> >
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Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
740-448-7328
303-328-5533