NEC 690.B1 Exception

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nkbhinge

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EE
I have a combiner box which is rated for 600A continuous duty. My combiner box output current is 374A. To comply with the exception of 690.B1 for 100% rating, can I go with 600kcmil AL which has the ampacity rating of 385A or do I have to go with conductors whose ampacity meets or exceeds 600A?
 
690.8(B)(1)?

The exception also involves the overcurrent device. So we'd need to know a bit about your fusing. If the overcurrent device rating(s) exceed 385A then your conductor would have to be larger to match the fusing.

Also does your 374A include the 125% factor in 690.8(A)(1)? Or is it done per 690.8(A)(2)?

Making up an example...If your combiner has 19 strings w a 15A fuse each (sum is 285A) and is listed for continuous use in that configuration, then I think you could use the exception and the 600kcmil.
 
The combiner box has 20A fuses for individual string conductors. The 374A is done as per 690.8(A)(2). I believe you have answered my question. Thank you so much.
 
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