[RE-wrenches] Square D DC disconnects

Mon Jan 11 16:43:44 PST 2010

David,

The state by the Eaton guy at SPI shows that person's lack of understanding.
The person I talked to was adamant that all disconnects had to be tested to
the disconnect standard that assumes a high (10,000-amp) current source
behind any fault. Switch openings are also tested based on the inductance in
the circuit since that has a major impact on the size and duration of the
arc-especially in ac systems.

Square D did an evaluation based on the limited fault currents and
inductance in PV system circuit that has no batteries. I believe their
evaluation is valid. The issue is that there is no specific test at UL
yet-that's why UL did not list it (I'm pretty sure they were involved at
some level, but that is impossible to prove). It will probably be added to
UL1741. Perhaps that was what the Eaton rep was referring-we'll give him the
benefit of the doubt.

I still use my basic rule similar to the rule for politicians-how do you
know if a marketing guy is lying?== his lips are moving.

Bill.

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of David
Brearley
Sent: Monday, January 11, 2010 3:41 PM
To: RE-wrenches
Cc: 'Tim Townsend'
Subject: Re: [RE-wrenches] Square D DC disconnects

Thanks, Bill.

Glad to hear you think the HU series is still a good option.

When I was making the rounds at SPI, I stopped by the Eaton booth and got
the sense that they were gunning for Square D. They made light of Square D's
self-certification of the HU series discos. The rep also made a statement
about the new Eaton dc discos being the only ones designed to meet UL1741
requirements. When I got home, the first thing I looked up was 690.4(D).
This doesn't say anything about dc disconnects needing to be listed to some
special PV standard. 

Is there a movement in this direction? Is there a UL1741 standard for dc
discos that is somehow different that the standard used for other dc
disconnects?

Best,

David 

On 1/11/10 5:28 PM, "Bill Brooks" <billbrooks7 at yahoo.com> wrote:

David and Kirpal,

It is ultimately up to the AHJ whether or not they accept the
Schneider/Square D self certification. That is a judgment call the installer
needs to clear with the AHJ. That being said, having Square D behind the
rating of a switch is a whole lot more than any one of the smaller companies
making equipment for the PV industry. 

I will continue to use the 30, 60, and 100-amp versions in the way
recommended by the manufacturer because it is a huge saving in cost and they
are well made switches. I will also check with the local AHJ before
installing them in case they are not going to pass it. You have to remember
you are working with one of the largest electrical suppliers in the world.
They have a huge reputation with local jurisdictions.

Eaton has been in the process of trying to make a big deal out of this issue
since they want a piece of the market. Fortunately, they are starting to
build products specifically for the PV industry, which I applaud. However,
they need to be given a hard time for the way they have tried to imply that
all Square D switches are not properly listed. They won't admit to that
because they would end up in a legal battle, but that is essentially what
they have been doing. Square D still has the largest selection of dc-rated
equipment on the market. Eaton has a long way to go. 

In a recent project that I reviewed, the engineer pulled the Square D
400-amp disconnect and replaced it with an Eaton disconnect at the
insistence of the Eaton rep. The Eaton product was not properly rated or
listed for the voltage while the Square D product was. This is the insanity
that needs to stop.

Bill.

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of David
Brearley
Sent: Monday, January 11, 2010 11:39 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Square D DC disconnects

Kirpal,

Have you checked out the SolarBOS disconnecting combiners? Their 28A version
might be ideal for large resi or small commercial applications. For larger
projects, Blue Oak PV Products and AMtec Solar also have disconnecting
combiners.

Thanks for sharing the updated Square D tech note. I had no idea that the
Square D HU Series disconnects were not UL-listed when used as described in
the older tech notes. The fact that this is not a UL-listed use of the heavy
duty safety switch, pretty much means that it is not an option for
integrators. As far as I know, there is no other product that is listed for
this use. 

David Brearley, Senior Technical Editor
SolarPro magazine 
NABCEP Certified PV Installer T
david.brearley at solarprofessional.com

On 1/9/10 4:14 PM, "Kirpal Khalsa" <solarworks at gmail.com> wrote:

Hi All......

I recently came across a revised technical bulletin from square D (
http://ecatalog.squared.com/pubs/Electrical%20Distribution/Safety%20Switches
/Heavy%20Duty/3110DB0401.pdf )......we have for years been using the Square
D DC Disconnect of various amperages (30, 60, 100) as disconnects leading
upto the inverter from the array.....we have frequently wired one string to
each of the three poles of the disconnect......we have had this
configuration inspected by inspectors regularly with approval
everytime......this new revision of the document from Square D shows this is
no longer a UL listed method.....they are now stating in this document that
they are "self certifying" this technique.......have any of you come across
this or know why Square D has back tracked? 

Something else I noticed is that they have raised the amperage rating on the
30A disconncect per pole by 2 amps from 18 to 20 which is good especially
when using higher amperage modules like Evergreen ES-A series which would
not have ben allowed to use the 30A disconnect as the short circuit current
rating was too high for the derated poles.  

This is not a huge concern as more and more of the inverters we are using
these days have an appropriate disconnect included with the inverter
negating the need for an additional stand alone disconnect.  

On a side note............Are there any other manufacturers making listed
muiti pole DC disconnects in which each pole can handle one string? Also
there is definately a need for roof mounted multi string (1-4 strings)
combiner boxes with integrated DC disconnects for residential applications
that have a reasonable price.......any one know if any?

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