Just in from Square D [RE-wrenches]

William Miller wrmiller at slonet.org
Thu Mar 8 12:25:59 PST 2001


Pals:

I just received some information from Square D:

1. A letter signed by Gary Shireman, Manager, Technical Support listing a
number of QO single phase main lug load centers that are UL listed for use
up to 48 VDC.  This is contrary to information I had received that
indicated that QO breakers were allowed to be used for DC only in NQOD
panelboards.  This is good news.  Among those load centers listed is the
QO612L100 RB.  This box makes a great combiner in that it is small (9.38
in. high), inexpensive (less than $50.00), it is Nema 3R and it is readily
available.

2. What about 24 and 48 VDC nominal systems?  My database shows that a
Siemens SR100 has an open circuit rating of 21.6 volts when configured as
12 volts nominal.  21.6 times 2 is 43.2.  There may be other de-ratings
required, and I believe these were addressed in an earlier post which I
will review, but at face value, it appears a QO breaker in certain QO
panels is UL approved for up to 24 vdc nominal systems.

I also received a document, signed by Mr. Shireman that states: "January 5
1999.  Letter of Certification.  This is to certify that the Square D type
QO single phase main lug load centers below can be applied at 125 VDC."
The table includes many QO load centers including the QO612L100RB that I
prefer.  How does a factory certification relate to UL listing?  Any ideas
out there on this one?

The above letter continues:  "Positive and negative voltages must be
applied to both bus bars.  Two pole circuit breakers must be used for
branch loads."  And, "Do not use the neutral assembly of the load center."

3. Also received was a photo copy of a UL label to place on a load center
that says:

"UL Listed Load Center Label.
Suitable for use on 48VDC max. systems.

For use on 48V DC max when using only 10-60 amp QO
branch circuit breakers rated 48V DC max.

Do not use QO-GFI or QO-AFI circuit breakers on DC
systems.
Short circuit current rating is limited to 5,000
Amperes when used on 48V. DC systems."

4. AIC rating.  I also received a bulletin, D-453 dated 7-86, Subject: DC
ratings.  It addresses battery based and generator based systems.  For
battery based systems it states:  "The duration of the high peak short
circuit current is usually not long enough to activate the magnetic trip.
Therefore, proper protection requires a breaker with a dc interrupting
capacity greater than the peak short circuit current and a magnetic setting
below the steady state short circuit current."  And, "To provide
appropriate thermal and magnetic protection, use a Square D "T" breaker."
And, "Note:  "T" breakers are not recognized by UL."

I expect one more bulletin.  In the meantime can we conclude:

A. Square D QO breakers in specified QO panels are UL recognized for 12
volt and 24 volt PV source circuits.

B. Square D QO breakers in specified QO panels are factory certified for 48
volt PV source circuits.  Each installer needs to convince his or her
inspector to accept the factory certification.  This may or may not happen.

C. Square D may not make a breaker suitable for battery connection.  Does
anyone know if the Heinman breakers do meet the requirements?  If we don't
have this info, can someone out there volunteer to research it (I have
exhausted my time budget on this subject)?  If the Heinman breakers are not
listed for battery connections, I say we are up s--- creek.


William



__________________________________________________________________
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
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