Inverter protection [RE-wrenches]

Tue Mar 6 22:42:05 PST 2001

Here is another post that talks about QO breakers.  See point 6.

William

>To: RE-wrenches at topica.com
>From: William Miller <wrmiller at slonet.org>
>Subject: Re: Inverter protection [RE-wrenches]
>Date: Mon, 11 Dec 2000 15:01:03 -0800
>Reply-To: RE-wrenches at topica.com
>X-Topica-Loop: 1300002502
>X-Sender: wrmiller at slonet.org
>
>Pals:
>
>This query brings up a number of issues for me:
>
>1. This group is for experienced installers sharing info to better
>themselves (or something like that).  I did not recognize the name of the
>gentleman inquiring, but maybe he should hire an experienced installer?
>
>2. The Trace DC Disconnect enclosures are way too small.  So are most
>electrical enclosures off the shelf.  In the case of the DC250, by the time
>you install two 250 Amp breakers, 4/0 wiring, two or three shunts with
>monitor wiring, a DCBB, an isolated bonding block required for a PVGFP, you
>are out of room.  I always liked the APT power centers for DC wiring only
>because they were so roomy (I never liked back tracking to route AC through
>them because it was awkward coming back around from the left side of an SW
>inverter and because they had no AC buss).  Also, the APT could be ordered
>with monitor wiring installed.
>
>Many RE systems require over sizing wire and that means an off-the-shelf
>load center or safety switch would have to be oversized to handle the wire
>as far as lug size and bending radius.
>
>3. The DC disconnects have no KOs for an AGC fuse holder.  This is required
>for monitor systems.  Not a big deal, I just drill for a chassis mount fuse
>holder.
>
>4. Over-current protection for sources can be a problem.  I always like to
>have OC protection and control for service in between each block in my
>system.  This is one advantage of a PVGFP: you can have up to 3 poles of
>disconnect for roof top arrays.  The TC and PM 60s (from Trace and/or
>Pulse) can be ordered with an integral breaker.  I have seen them wired as
>input and as output breakers, and I have changed them in the field, as
needed.
>
>I do also frequently use the add on breakers in the sides of the Trace DC
>disconnect enclosure, but this makes the enclosures even more crowded as
>the breaker can hang over internal equipment.
>
>5. The tap connection on the Trace DC disconnect breakers is ludicrous.  It
>is a code violation (and against common sense) to put two leads under one
>lug.  Trace would have you put a lug under the bolt head holding the main
>lug onto the breaker, but this is so difficult to do, especially after
>wiring 2/0 or 4/0 to the main lug.  I have also stripped the threads in
>this lug.  I can't imagine the breaker manufacturer condones this practice.
>
>I don't particularly mind using a short piece of #6 wire from a battery
>connection to a circuit breaker.  This wiring philosophy is covered under
>the tap rule in the NEC.  I've never seen it directly related in print to
>DC wiring, but the principal is the same:  You can protect a length of wire
>either at the beginning of the wire or at the end.  If the wire is long, it
>is safer to protect it at the upstream end.  If the wire is short and well
>protected mechanically, it may be as safe to protect it from over-current
>at the down stream end.
>
>6.  One place to install over-current protection and switch control is in
>the PV combining box.  An article in HP demonstrated building a very nice
>combining box for a PV array.  I prefer using off-the-shelf items, were
>practical.  A Square D QO load center can be used, but the QO breakers are
>DC rated only for installation in an NQOD panel.  The NQOD panels are 3 to
>4 times the cost of a QO panel.  I use the QO panels anyway, even though I
>know it is technically wrong.  I'd like to know exactly why the QO panels
>are not rated for DC, and possibly start a letter writing campaign to
>Square D to have them test the QO panels for DC and submit to UL for
>certification.  Does anyone have any insight in this question?  If you want
>to bolt down breakers, the QOU are DC rated and can snap on a DIN rail.
>You need to create a buss, if required.
>
>7. I have never had my hands on a Trace Power Panel (IPPS) but I have
>reviewed the drawings, and I see some possible shortcomings:  I'm not sure
>where one connects a grid input.  Has anyone done this?  Is it safe to
>bypass the AC input to one inverter and not the other (which is possible
>with the separate transfer switches)?  I do not like to plumb to an SW
>inverter via the end panel KOs since this obscures the AC connections as
>well as the relay and temperature sensor connections, however this is done
>in the IPPS.  Also, I would not relish handling the weight of an IPPS.
>
>Generally speaking, since each installation has its own unique
>requirements, an IPPS can not be guaranteed to fit all needs.  I prefer to
>custom build to satisfy these unique needs.
>
>
>William Miller
>
>
>At 04:23 AM 12/4/00 -0800, you wrote:
>>I have a question for the expertise of this group.  We are in the final
>>throws of completing a system (2 racks of 4 ASE 300W modules on trackers and
>>3000W Whisper (I think), 2 Trace 5548s for 240V on a Trace Power Board,
>>about 2000 Ahr battery bank, 20Kw generator, purchased as a package from
>>Kiocera ("It will take an electrician only a few hours to get it up and
>>running!")).  The power inputs (PV and wind) are connected to the inverter
>>side of the 250A battery disconnects, which is our question.  It seems to
>>leave the inverter unprotected - you're able to isolate the batteries, but
>>to isolate the inverter you need to turn off the PV and wind input
>>separately.  This would seem to make sense, but it seems that an inattentive
>>or inadequately trained homeowner might easily turn off the battery main,
>>thinking they were disconnecting power to the inverter, when in fact the PV
>>and wind would still be powering the units.  We actually did this (left only
>>the wind connected), and one of the inverters smoked.  So, I would
>>appreciate any thoughts and/or remedies.
>>Doug McCorkle
>>Sunnyside Solar
>>
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>
>__________________________________________________________________
>William Miller
>SLO Communications: Communications and Power Systems Consulting
>Chief Engineer, KCBX: NPR and PRI for San Luis Obispo and Santa Barbara
>PO Box 50, Santa Margarita, CA 93453
>Voice :805-438-5600		Fax: 805-438-4607	VMail: 805-546-4875
>email: wrmiller at slonet.org
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>
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>
>___________________________________________________________
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>Newsletters, Tips and Discussions on Your Favorite Topics
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__________________________________________________________________
William Miller
SLO Communications: Communications and Power Systems Consulting
PO Box 50, Santa Margarita, CA 93453
Voice :805-438-5600		Fax: 805-438-4607	VMail: 805-546-4875
email: wrmiller at slonet.org
License No. C-10-773985
_____________________________________________________________
Compatibility:
Word processor: WP7
Spreadsheet: Quatro Pro 7
CAD: Microstation 95, DXF, Visio 4.1T
_____________________________________________________________
"I stand by all the misstatements that I've made." Dan Quayle
__________________________________________________________________

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