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re: string sizing for your 2500 watt inverter
18 oct 2002
dlehmicke  wrote:

>nick, i can't imagine you feeling restrained by nec requirements...

we doan need no steenkeeng nec...

>in addition to the sunnyboy max open circuit voltage (temperature corrected)
>limit for input strings...

...which need only apply if it never sees 600 v, eg if a thermostat
shorts out a few panels. not as efficient as a circuit that does this
in the rare event that the sunny boy input exceeds 600 v, but simpler.
this should be part of the sunny boy. good cherman engineerink.

>there are at least three other reasons not to exceed 600 v open circuit:
>
>1.  the nec, article 690, limits pv system voltage (voc) to 600 v.

see above. 

>2.  common conductors like thwn, use-2, and xhhw-2 are listed as 600-v
>conductors.  higher voltage conductors are available.  the mc cables shipped
>with some pv panels are use-2, lisgted for 600 v operation, max.

see above.

>3.  common dc disconnect switches, like the square d hu361, gethn2261rdc,
>and the siemens hnf261r are limited to 600 v circuit switching...

see above.

nick




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