[RE-wrenches] Square D DC disconnects

Mon Jan 11 16:55:12 PST 2010

Thanks for the clarification, Bill. If they add this to UL1741, I hope they
will do so in a manner that recognizes the unique characteristics of PV
applications. Definitely easier to interrupt a 10A source than a 10,000A
one.

On 1/11/10 6:43 PM, "Bill Brooks" <billbrooks7 at yahoo.com> wrote:

> David,
>  
> The state by the Eaton guy at SPI shows that person¹s 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‹that¹s why UL did
> not list it (I¹m 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‹we¹ll 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 D¹s
> 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
> doesn¹t 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 won¹t 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 
> 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/H
> eavy%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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David Brearley, Senior Technical Editor
SolarPro magazine 
NABCEP Certified PV Installer 
david.brearley at solarprofessional.com
Direct: 541.261.6545
Fax:  541.512.0343

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