600 VDC switches [RE-wrenches]

[William Miller]

Matt:

I believe you missed the thread some months ago (or maybe a year or so?) in
which I shared some research on Square D breakers.  They are UL rated for
45 VDC and factory certified for 125VDC.  As it was put so succinctly by, I
believe, Bill Brooks UL trumps factory certification, so you can't argue
the 125 VDC rating to the inspector.  This is all regarding single pole
breakers.  I doubt that one could extrapolate a 600 VDC rating on any
number of poles for Square D breakers given the 45 VDC limits on 1 pole.

My original post that started the discussion on 600 VDC switches referred
to a Siemens catalog page in which a two pole breaker was wired in series
to achieve some higher voltage rating.  I don't know the breaker or the
rating, but I'm curious now and I will try to find out more.

I hope this clears up any confusion I may have caused.

William


At 09:21 AM 9/18/02 -0700, you 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. I'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
>----- Original Message -----
>From: "William Miller" <wrmiller at slonet.org>
>To: <RE-wrenches at topica.com>; "John Berdner" <jberdner at sma-america.com>
>Sent: Tuesday, September 17, 2002 9:42 PM
>Subject: 600 VDC switches [RE-wrenches]
>
>
>> Colleagues:
>>
>> Those of you who have installed the Sunny Boy inverters have used the 600
>> VDC rated switches, such as the Siemens HNF261.  It is interesting how the
>> manufacturers achieve the 600 volt rating:  They use a 3 pole disconnect
>> and put two of the poles in series.   This way, the contacts break two
>> times at the same moment.
>>
>> A few months ago I was unable to obtain a 2 pole 600 VDC disconnect in
>> short order, so at the same price I was able to purchase a three pole
>unit.
>>  Lo and behold, the series jumper was missing and the cover showed a
>rating
>> of only 250VDC.  I since learned that because only three pole devices are
>> commonly manufactured, if you need to use all three poles separately, you
>> can not occupy two of them in series, therefore you can not achieve the
>600
>> volt rating.
>>
>> Should we switch the positive lead?  I submit that there may be a safety
>> advantage to switching the negative.  The Sunny Boy takes the negative to
>> ground.  If the negative is left connected, the array still has potential
>> to ground.  If the negative is switched, the array is floating, therefore
>> no (or less) shock hazard.  We know this because my helper got zapped
>> today.  We are still discussing the ramifications so as to avoid this in
>> the future.
>>
>> Here's another idea:  Why not switch both leads?  Siemens has a circuit
>> breaker that does the same trick, and the Siemens catalog contains a
>> drawing that shows one side of DC going through the two series poles and
>> the other side going through the one pole.  Is this how I should be wiring
>> the DC disconnects for Sunny Boys?
>>
>> (BTW, the drawing on the cut sheet for the SB1800 shows only the positive
>> switched through one pole.)
>>
>> Thanks for considering these nit picky, nerdy questions.  I believe it is
>> in considering these details that safety is achieved.
>>
>>
>> William Miller
>>

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William Miller
Miller Power and Communications
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