PV rating norms [RE-wrenches]

William Miller wrmiller at charter.net
Tue Dec 11 09:23:03 PST 2007


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Friends:

First off, sorry about the long winded request for help on PV rating.  The 
discussion can be boiled down to this exception to 
690(8):  Exception:  Circuits containing an assembly, together with its 
overcurrent device(s), that is listed for continuous operation at 100 
percent of its rating shall be permitted to be utilized at 100 percent of 
its rating.

This exception specifies not just the device but also the circuit, so I 
believe we can avoid use of the 125% factor when considering the charge 
controller and the circuitry into and out of said charge controller.  This 
is assuming Xantrex listed their device for 100% duty, which I am assuming.

Regarding open circuit volts:  Here is another case of the NEC being in 
conflict with the manufacturer's sizing tool.  The NEC requires a 
correction factor of 1.13 for our climate zone.  This puts three strings 
just over the listing of 150 VDC, even though the manufacturer's sizing 
tool allows strings of 3 (although just barely).  It is common sense that I 
must satisfy both...

Thanks for the "input".

William


-- _________________________________
William Miller
Miller Power and Communications
Voice :805-438-5600     Fax: 805-438-4607
email: wrmiller at mpandc.com
http://mpandc.com
License No. C-10-773985


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