Combiner box alternate solutions [RE-wrenches]

[Phil Undercuffler]

Spent a little time web crawling/tech support phoning this morning looking
for alternatives to the combiner box in specific and DC rated fusing in
general, and I figured I'd share my results.  I'd be interested in hearing
your responses and feedback.

Two classes of fuses are both easily found, relatively affordable, and have
DC ratings;  Class R and LP-CC "midget" fuses.  (Grainger sells
Cooper-Bussmann brand, all nomenclature and part numbers here are based on
their system, I'll leave the cross-referencing to you).  All could be
installed in a 3R box on the array pole for series fusing with the outputs
paralleled to larger conductors or even inside the power system if you wish
to run separate conductors for each series string.

We've used FRN-R fuses for years, they're available in a wide range of
sizes, and they're rated for 125 volts DC with 20k amp interrrupt rating.

A new find this morning was the LP-CC series.  They're UL Listed for 300
volts DC, 20k AIR, available up to 30 amps.  There is both a conventional
open frame fuse block (grainger #4xc34, $4.26 single pole) a Square D fuse
block with integrated fuse puller (#5b375, $65.10 pack of 10) that snaps on
a DIN rail, and a Bussmann "Touch-Safe" block that either bolts down or
snaps on a DIN rail (#5kk42, $6.92 ea).  I've got one of the last on order
to check out, I'll post what I find.  But it looks like a way to have a
user-serviceable low current low cost fused disconnect, although not in a
box.

Interestingly enough, there appears to be no UL listed 1/4" fuse available,
only UL recognized.  We've been using ABC fuses in an inexpensive block for
years for meters and occasionally series fuses for small arrays (not to
mention every system with a Trace/Pulse Combiner!) they can be bounced by an
inspector for not being DC rated or listed.

Also, be wary of manufacturer's cross-reference charts.  I'm finding that
they are only applicable for AC ratings, not DC.  There's a whole alphabet
soup of fuses available, and one manufacturer's midget fuse might be
interchangeable with another on an AC circuit but not on DC.

More to follow

Phil

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