[RE-wrenches] Gray code area

Drake Chamberlin drake.chamberlin at redwoodalliance.org
Wed Jul 30 15:56:38 PDT 2008


At 09:48 AM 7/30/2008, you wrote:
>Drake:
>
>I'm sorry, but this isn't making any sense.  Here is what I understand:


>1. There is a commercial building that you would install a grid-tie 
>PV on the roof.

Yes.

>2. The commercial building has a service that you will not feed the 
>grid-tie to.

Yes.  It also has its own service.  The commercial building gets some 
solar also.  The tax benefits would be for it all to be on the 
commercial service, but we are following the owner's request.

>3. This commercial building has a "feed-through" breaker panel that 
>was installed for the PV to tie to.  This "Feed-through" box does 
>not connect to the commercial service.

Yes

>Where is the service that the PV system would feed?  In a separate building?

Yes, in the residence on the property.  The meter is on the 
commercial building.


>Where does the feeder connected to the bottom of this "Feed-through" panel go?



It goes to the residence, which is another building on the same property.

Although unusual, the local code authorities are fine. In general, I 
don't see any code conflicts.  The commercial meter is for farming 
operations.  The residence is located on the same property.  This is 
a variation of the standard farm service, which has a central pole 
with meter and distribution to a number of buildings.  This has two 
meters on the same structure, and distribution from there.

Drake


>William Miller
>
>At 10:24 AM 7/30/2008, you wrote:
>>Thanks to All who have replied,
>>
>>First, to answer William's question
>>
>>"What is a "feed-through" breaker box and what are "feed-through" lugs?"
>>
>>A feed through panel is the type of service equipment often 
>>installed on pre-manufactured homes, where a main switch is needed 
>>outside the building, and a limited number of loads, fed from the 
>>outside, are also supplied.  On the bottom of the busbar,  there 
>>are lugs equivalent to the lugs for the service entrance cables.
>>
>>This is useful when feeder is to be installed to supply the breaker 
>>panel in the premise that is equal to the total service 
>>amperage.  No breaker is needed for the run to the subpanel inside, 
>>since the wiring will be equivalent to the service cable.   It is 
>>similar in function to a disconnect switch, but will typically have 
>>4 to 8 breaker spaces.
>>
>>The situation in this project is that a feed through panel is in a 
>>separate building from the building to be supplied from that 
>>panel.  The building this panel is in has a separate electrical 
>>service, which is commercial.  The service for the residence comes 
>>in through a separate meter, located on this  same commercial 
>>building, then goes to the feed through panel.  This panel was 
>>installed for us, for the sole purpose of allowing a feed from the solar array.
>>
>>The issue here is that the busbar will have 200 amps from the main, 
>>and over 40 amps from the solar.  No power is to be taken from the 
>>residential service to feed the commercial building.   There is no 
>>possibility of an overload on the busbar because the house has a 
>>main 200 A breaker that will limit the load from the panel.
>>
>>It could be argued that since the line to the house will have up to 
>>240 amps available on a 200 amp service, that is too much.  I would 
>>argue that a standard service drop can supply 10,000 amps instantaneously.
>>
>>The box is strictly to be used as an AC combiner and feed for two 
>>inverters.  By the letter of the NEC, it does not seem to be 
>>code.  I'm going to use Kent's suggestion and use a label, after 
>>running it by the AHJ beforehand.
>>
>>
>>-Drake
>>
>>
>>At 10:14 AM 7/29/2008, you wrote:
>>>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: re-wrenches-bounces at lists.re-wrenches.org
>>>>[mailto:re-wrenches-bounces at lists.re-wrenches.org] 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 <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
>
>
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Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
740-448-7328
303-328-5533 





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