Friends:
There are two issues brought up here: Designation of a load center as a
"grid-tie combiner" and point of connection.
Grid-tie combiner: The concept is to designate a load center as a
"grid-tie combiner" and not allow any load breakers to be installed. While
I completely agree with the concept, you have to convince your
AHJ. Putting this load center in a location where only competent workers
have access may help your case.
Point of connection: There is some confusion in the original e-mail. What
is a "feed-through" breaker box and what are "feed-through" lugs? I looked
in the NEC and that combination of words occurs only twice and neither case
seems to apply.
I assume that some breaker panel on the premises feeds loads. All such
load centers, be they sub-panels, main panels or meter/main panels, need to
satisfy 690.64(B). Every buss that receives locally generated power and
also feeds loads must comply. Even if there is not a breaker in a given
panel directly from an inverter, if there is a breaker feeding a sub-panel
that accepts inverter power, that panel must comply.
I have posted a drawing that illustrates this concept at
http://mpandc.com/case_studies/case_studies.html Click on the Point of
Connection link. Note that the sub-panel does not comply because only 25
amps are allowed and 29 amps are connected. The meter/main does comply.
I hope this explanation helps shed some light on the subject.
William Miller
At 02:21 PM 7/28/2008, you wrote:
Drake and all,
If I understand your thread, you are connecting through an extra 200-A
breaker in a box with two 200-A services. If this service was originating
from the utility, everything would be good and you would be making a
690.64(A) supply side service connection. If the connection at the main
service is in fact feed-through lugs with no service disconnect, then the
200-A breaker the PV is connected to is still a line-side connection and
everything is fine--690.64(B) does not apply. I assume this system has 6,
20-A breakers for a total of 120-A of supply fed through a 200-A breaker
(actually the 200-A breaker doesn't even matter--all that matters is that we
are less than 200-Amps).
I may have misunderstood something here, but 690.64(B) is a load side
connection section and must have loads in order to be considered load side.
With no loads on the line side of the service disconnect, we are simply
creating another service disconnect (see previous discussions on numbers of
disconnects and service definitions).
The bummer with the way the code is written is that as soon as a load is
added, everything changes. We are working on a proposal that would make that
situation easy, but right now it is a pain. The 2008 NEC in 690.64(B) is a
huge step forward to allow small PV systems, relative to the service, to
connect to the load side of the service legally without having to change out
the service equipment. There are those that still oppose this idea, so we
need to continue to fight to keep what we have and to expand it beyond the
120% limit. Objections still get raised routinely, and those concerns must
be silenced with test data and good engineering analysis.
Bill.
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Drake
Chamberlin
Sent: Monday, July 28, 2008 1:03 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Gray code area
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 <[EMAIL PROTECTED]>
>To: RE-wrenches <re-wrenches@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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