Inverter protection [RE-wrenches]

Mon Dec 11 18:01:03 EST 2000

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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To send a message:
 RE-wrenches at topica.com

The archive of previous messages: 
 http://www.topica.com/lists/RE-wrenches/

To unsubscribe send a message to: 
 RE-wrenches-unsubscribe at topica.com

To check out the other RE-Wrench participants:
 www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine: 
 www.homepower.com

For info contact list moderator by email:
 michael.welch at homepower.com

___________________________________________________________
T O P I C A  http://www.topica.com/t/17
Newsletters, Tips and Discussions on Your Favorite Topics