DC-GFP/2 protection [RE-wrenches]

[Christopher Freitas - OutBack Power]

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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