John Wiles & 600 VDC switches [RE-wrenches]

[Bill Brooks]

Jeff,

So the good news is that all the SMA inverters installed previously with
Square D disconnects are now legal when before they were really not legal,
but nobody knew so nobody cared.

So now the question remains whether it is legal to install an SMA inverter
with any other brand of disconnect so to be on the safe side only use Square
D.

I'm working on the arc affinity issue in my mind. Sounds very cool, but I
have a real hard time believing that the arc will have any affinity for
anything but the contact it just came off of. Maybe if it was AC the
restrike could get confused, but I need to talk to a UL guy before I buy the
affinity argument.

I love the education PV systems supply--ain't it fun?

Bill.

-----Original Message-----
From: Jeff Oldham [mailto:starpower4u at juno.com]
Sent: Tuesday, February 11, 2003 11:27 AM
To: RE-wrenches at topica.com
Subject: John Wiles & 600 VDC switches [RE-wrenches]


I always thought that you needed a dedicated disco per inverter so I asked
John Wiles about it as I could not find a code referance to support my
misimformation. It turns out it is OK to have up to 3 SB's on a single 3
pole disco as stated by John Berdner. There does seem to be a possible
disagreement about combining strings on a disco pole. It seems that Berdner
has been very closely involved in this and is probably right about the
double conductors/single lug combining. Most importantly, it seems that this
applies to SB inverters ONLY at this time anyway.

John Wiles asked that I post his message for him:

Jeff:


Here is your answer and please post the following on the Wrenches Web site
for me.


The PV Industry (at least one PV engineer got the call/letter) has been
formally notified by Square D (in December) that the HU361-R disconnect and
other similar Square D fused and unfused disconnects rated at 600 volts DC
are not suitable for use on grounded PV arrays even when the poles are
connected in series and switch only the positive conductor of the PV array.
The use of these disconnects in this manner violates the UL Listing on the
product and therefore also violates the provisions of the NEC.  Both
positive and negative conductors must be switched and the power system must
be ungrounded to meet the listing requirements.


Siemens and GE "say" that they have appropriately rated disconnects (600
volt dc, grounded systems), but the tech people have been unable to provide
substantiation.  Furthermore these switches appear to be tested to the same
UL Standard that is used to test the square D disconnects and that standard
uses ungrounded power supplies and ungrounded loads.


For the techies. Having the switch enclosure connected to one of the circuit
conductors (as it must in a grounded system) may create additional
electromagnetic/electrostatic static forces on the arc causing it to strike
the grounded enclosure or move out of the normal arc chute charring the
insulation.  If the  enclosure is grounded, but neither of the circuit
conductors is grounded or connected to the enclosure, then there is no
electromagnetic/electrostatic affinity between the arc and the enclosure.


The good news is that UL, Square D, and SMA have run special listing tests
on the HU361-R disconnect and when used only with the SMA SunnyBoy
Inverters, the special listing says OK for 600 volts per pole, grounded
systems, one pole per string. This means that up to one string may be
connected to each pole of the switch (up to three strings) and combined in
one Sunny Boy inverter or that the separate strings can be connected to
three separate inverters.   The lack of backfeeding from the Sunny Boy
facilitated the testing for this special listing. Installers/systems
Integrators should contact SMA/Square D Applications Engineering to obtain a
copy of the Special Listing on the HU361-R.



Jeff Oldham


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