600 VDC switches [RE-wrenches]

Mon Feb 10 16:03:50 PST 2003

Wrenches,

Good news from Square D on this thread. I found out today that Square D has
received UL approval for use of the HU361 in PV systems up to 600VDC and not
more than 13A per pole (no series switching or negative switching is
required - 3 poles, 3 positives). See letter from Square D below.

E. H. Roy
Solar Works, Inc.
64 Main Street
Montpelier, VT 05602
1-800-339-7804 ext. 306
ehroy at solar-works.com

	DATE:	2/10/03
	TO:	E. H. Roy - Solar-works, Inc
	FROM:	Bob Miller - Square D Company
	SUBJECT:	Photovoltaic application of Safety Switches

E.H.,

Square D Company has obtained UL listing (File E2875, Vol. 1) for 30 amp
non-fused heavy duty switches, HU361, HU361RB, HU361AWK and HU361DS,  for
use on photovoltaic systems. The 2002 National Electrical Code does not
allow the negative conductor to be broken when operating switches on
photovoltaic systems.  The above mentioned switches may be used on
photovoltaic systems as shown below as long as the line voltage per pole
does not exceed 600 Volts DC and the normal rated current per pole does not
exceed 13 Amps DC.

Bob Miller
Application Engineer
Square D Company
859-243-8069

-----Original Message-----
From: jberdner at sma-america.com [mailto:jberdner at sma-america.com]
Sent: Friday, October 11, 2002 3:06 PM
To: RE-wrenches at topica.com
Subject: RE: 600 VDC switches [RE-wrenches]

Wrenches:

We are in very close contact with Square D concerning the HU361 switch.
We are talking with several people inside the company including the
product engineer responsible for the switch.  It >> might << be possible
to use the switch at up to 600 Vdc but certainly NOT at 30 Amps.  We are
running some UL tests soon and will report the findings.

Square D tech support is incorrect concerning the Listing with 1 pole in
series at 600 Vdc. Technically the Switch is UL Listed for 600 Vdc motor
loads (rectified 480 Volt, 3 phase).  In that configuration they
recommend putting one pole in the positive to the load and one pole in
the negative to the load.  If you are wiring 2 poles in series then it
makes sense to separate them as far as possible so use the two outside
poles.  For PV systems, Article 690 prohibits the use of a switch in the
grounded conductor (but GFDI's are allowed) so Square D suggests wiring
2 poles in series with (both in the positive conductor) hence a jumper
between the poles.

RANT ON:
The whole grounding paranoia we have here in the US makes no sense to
me.  It seems like the regulatory and inspector community has had
"ground everything" beaten into them for so long they have forgotten to
ask why we do it in the first place. IMHO, the array should be floating,
not grounded, at all times and certainly when you work on it.  Solidly
grounding the array gives you a single fault lethal hazard which seems
stupid to me.  Fortunately the Sunny Boy's ground fault fuse IS the
connection to ground and it is allowed to be there by Code because it is
part of the GFDI.  I STRONGLY suggest everyone should remove the GFDI
Fuse (after you open the DC disconnect of course) when ever you are
installing or servicing the array.  DO NOT assume, however, that the
array is ungrounded since it could have a ground fault or other problem.

Remember: A dead arrays is like an unloaded gun - There ain't no such
thing.
RANT OFF:

A couple other points on the Listing of the HU361 - The terminals are
approved for 2 wires per terminal so you can parallel the positives for
two strings in the dc disconnect.  Also be sure to wire the array
positive to the line side of the pole 1, the jumper from the load side
of pole 1 to the line side of the pole 3, and the inverter to the load
side of pole 3.

If you have any questions, or if I can be of any further assistance,
please do not hesitate to contact me.

Best Regards,

John Berdner

SMA America, Inc.
12438 Loma Rica Drive, Unit C
Grass Valley, CA  95945
530.273.4595 (voice)
530.274.7271 (fax)

-----Original Message-----
From: EH Roy [mailto:ehroy at solar-works.com]
Sent: Thursday, October 10, 2002 3:29 PM
To: RE-wrenches at topica.com
Subject: RE: 600 VDC switches [RE-wrenches]

Brad,

I remember that arcing problem, but don't remember the brand of
disconnect
it occurred in.

Square D technical support tells me I don't have to wire two outside
poles
in series to get a 600VDC rating on their HU361 - switching of one
positive
through one pole is appropriate and covered by the UL listing. They are
still scratching their heads about how many positives can be switched in
one
disconnect.

E. H. Roy
Solar Works, Inc.
64 Main Street
Montpelier, VT 05602
1-800-339-7804 ext. 306
ehroy at solar-works.com

-----Original Message-----
From: Brad Bassett [mailto:bsbassett at earthlink.net]
Sent: Wednesday, September 18, 2002 4:32 PM
To: RE-wrenches at topica.com
Subject: RE: 600 VDC switches [RE-wrenches]

Matt,

I believe that Sq D does not put the necessary jumper in at the factory
between the two poles to get the 600vDC rating. The lebelling on various
disconnects has sometimes been lacking also. Although GE has supplied
the jumper for many years, their labeling was confusing. It now appears
that they got the message and the labelling is clear and they call out
the difference between the single pole 250v DC rating and the two pole
break 600vDC rating. I don't know what the other mfg's do.

Back almost a decade ago, we had someone in the field installing our
first 600vDC array and used a single pole, which when opened sustained
an arc until they literally blew it out. In our subsequent conversations
with various disconnect engineers we learned that a single pole will
come close to breaking 600v and sometimes will depending on current etc.
But to be reliable and meet UL testing, breaking two poles is needed at
these voltages.

Brad

matthew tritt wrote:
> William,
>
> Your questions bring up some very interesting points. I did an install
> yesterday using a Sq D 3 pole breaker which has no jumper and no
mention
> anywhere of a decreased rating. > > manufacturers achieve the 600 volt
> rating:  They use a 3 pole disconnectI'm going to check with the
> distributor and
> see if I can get an answer on the need to add a 3rd breaker to the
> system,
> or if these switches are actually rated @ 600 volts per contact.
> Also, I regularly used to switch both DC inputs until I was admonished
> by an
> electrician who insisted it was illegal to break the negative lead. I
> believe that he said this because of his assumption that the neutral
in
> AC
> is grounded and it would be somehow interrupting the ground to break
the
> neutral on the DC circuit as well. Why not switch both?
>
> Matt

Brad Bassett
Schott Applied Power
Tumwater, WA office
bsbassett at earthlink.net

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