620 VDC [RE-wrenches]

[Bill Brooks]

Joel,

While I don't disagree that some modules are not optimal for some inverters,
the idea that all AHJs insist on using all-time low as a guide for "lowest
expected ambient temperature" is a myth. There is no guidance in the code on
the subject. That is precisely why we intend to add guidance. Until now,
when asked what to use for the number, my response is that all-time low is
the most readily available appropriate number.

Bill.

-----Original Message-----
From: Joel Davidson [mailto:joel.davidson at sbcglobal.net] 
Sent: Thursday, June 26, 2008 6:43 PM
To: RE-wrenches at topica.com
Subject: Re: 620 VDC [RE-wrenches]


The NEC is very specific about 600 volts DC and AC in Chapter 1, paragraph 
2. The 600-volt Rule is that fundamental. Almost all AWJ and Code Priests 
interpret Article 690.7 "lowest expected ambient temperature" as the lowest 
temperature recorded by their chosen Weather Scribes even if that low 
temperature only happened once many years ago. From a practical standpoint, 
some solar modules can not be used optimally with some inverters. Every time

I get a good module/inverter match, the manufacturers change specs, 
availability, price, or all three.

----- Original Message ----- 
From: "Drake Chamberlin" <Drake.Chamberlin at redwoodalliance.org>
To: <RE-wrenches at topica.com>
Sent: Thursday, June 26, 2008 12:37 PM
Subject: 620 VDC [RE-wrenches]


>
> Hello Wrenches,
>
> Some inverters are able to withstand voltages above 600 VDC.  The 
> Solectria 95KW can take up to 620 VDC without harming the electronics.
>
> If we size a system so that the record low temperature is gives a voltage 
> of under 620 VDC, a viable system can be installed.  There is a question, 
> however, about the Code compliance of this, since building wire is rated 
> at 600 volts.  Higher voltage wiring is available, but will likely not be 
> cheap or convenient to use.  Also, what about 600 V modules and PV cable?
>
> Since this is DC, there are not any cycles to create a voltage peak.  A 
> 600 VAC RMS nominal system can have (if my calculations are correct) a 
> peak voltage of close to 850 volts.  Also, system voltages can range up to

> 10% from the nominal, resulting in voltages of as high as 660 VAC RMS on 
> 600 volt systems.
>
> The question is, "can we have a system with a possible low-temperature, 
> open circuit voltage of 620 VDC with wiring and modules rated for 600 
> volts?  Can the other 20 volts be considered within the nominal range?
>
> Thanks,
>
> Drake
>
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