DC-GFP/2 protection [RE-wrenches]

[Travis Creswell, Ozark Solar]

----------
>From: jberdner at sma-america.com

>Yes, if you use the GFDI breaker as a disconnect then the system becomes
>ungrounded when you disconnect the PV.  Here in the US, many of the code
>
>
>Best Regards,
>
>John Berdner


Ok, I'll admit that I'm not following this to well, plus I have done so few
roof mounts I'm not up on Ground Fault protection for solar arrays.  Given
that I have my first installation with these  DC-GFP/2's is coming up soon I
need to ask some questions.  How is the "system" becoming ungrounded when
you disconnect the array?  Perhaps I don't understand what you mean by
"system".

Looking at the PSDC diagram on page 29 of the "Outback Catalog and System
Design Handbook".  Thanks to Outback for sending that by the way.  Pretty
handy book for those who don't have one yet.  I see the wiring method and
the negative array is not involved. Right?  There appears to be a breaker
per sub-arrray with each one feeding the the bottom of the DC-GFP/2 breaker.
 The two poles on the output side of the DC-GFP/2 then feed two charge
controllers which then are connected to the positive buss via two more
breakers.  The good news is that at least the DC-GFP/2 is a two pole unit.

Whew, seems like a lot of hassle for Ground Fault protection which I (and
many others) never have quite grasped the need for.  How does a breaker in
the load center stop the array from feeding the fault which is somewhere
between the array and load center?  I can see how GFP stops the battery from
feeding the fault when it's only a low amperage, intermittent fault which
probably wouldn't trip the Charge controller's breaker.  I'm sure if it was
explained to me I would understand it better.


Thanks
Travis Creswell
Ozark Energy Services 
----------
>From: Christopher Freitas  -  OutBack Power <cfreitas at outbackpower.com>
>To: RE-wrenches at topica.com
>Subject: RE: DC-GFP/2 protection [RE-wrenches]
>Date: Thu, Aug 22, 2002, 10:28 AM
>

>The OutBack DC-GFP/2 actually includes two 70 amp breaker poles in its 
>current form.  This was required by the breaker manufacturer to allow 
>them to mark the assembly as a "UL Listed" device.  The amperage is 70 
>to allow for coordinated tripping if an overload occurs (the DC-GFP will 
>not trip first - the 60 amp breaker will trip instead).  We are 
>considering eliminating the redundant overcurrent protection in the 
>DC-GFP but it does offer some benefit if it is not installed properly. 
>
>John Berdner is correct that much of the world does not ground the 
>negative conductor and that grounding probably causes as many problems 
>as it solves.  In the US you can operate low voltage (less than 50 volts 
>DC) ungrounded - BUT - then you need breakers in both the negative and 
>positive conductors as they are both now ungrounded.  
>
>Given the low cost of breakers and the space in our PSDC enclosure to 
>mount up to 16 breakers - I think that the extra breakers are a 
>reasonable addition to ensure safe installations.  
>
>Christopher Freitas
>OutBack Power Systems, Inc.
>cfreitas at outbackpower.com  www.outbackpower.com
>Tel 360 435 6030  Arlington WA USA
>

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