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Question about running data gathering cat5 cable w/ DC solar array wiring..

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Posted by Rick F on January 2, 2008, 10:55 pm
Hi all and Happy New Year..

I've got a question for you.. I've got a couple of Fronius inverters
installed on the side of my house and have the COM cards plugged in..
Now, I need to hook up the daisy-chain cables to/from each router --
no biggie. However, I need to run the end of the cable to my garage
where the rest of the Fronius equipment (sensor box, data logger box)
will be mounted for easier maint -- a distance of approx 75ft.
Anyway, I can punch-out one of the plugs on the last inverter and run
rigid conduit from it to the attic and go from there -- OR I can use
the existing rigid conduit that houses the high-volt dc cables from
the solar array and run the CAT5 cable together with them for a
distance of approx. 10 feet or so..  I realize that you should not run
data cabling in parallel with AC (high-volt) lines to avoid noise and
other issues, but is this also an issue w/ high-volt DC lines as
well?  I'd like to avoid running more conduit if there's no issue here
but will if anyone thinks I might have some sort of issue w/ noise
from the DC power lines.. Thx!

Posted by Rick F on January 2, 2008, 11:21 pm

[ ... ]

In thinking about it more, I realized that PoE (Power-over-Ethernet)
does exactly this -- it runs a DC power source down a pair of the CAT5
lines w/o any sort of issue -- the only difference is the amount of
voltage (PoE is 48vdc), but each leg of my solar array is closer to
275vdc if I recall.. I guess I'm leaning towards running them in the
same conduit..

Posted by daestrom on January 3, 2008, 10:15 pm

One issue you may find yourself up against is your local electric code.
Generally... HV power cabling is not allowed inside the same conduit as
'communication' cables.  The concerns are that if the higher voltage cable
faults to the comm cable, you'll have voltages in equipment that can't
handle it and isn't fused/protected against it (i.e. 275 VDC in a network
card is a *bad* thing)


Posted by Rick F on January 4, 2008, 5:52 pm


Thanks for the info.. I've yet to do this work (too many other things
that are higher priority) but
will pursue putting an extra conduit run to do it "right" the first
time (no rework later if there's
a problem)..

Posted by Martin Riddle on January 2, 2008, 11:46 pm

Most likey there will not be a problem. But if the Fronius is spewing noise on
the DC buss then a Ferrite bead or two may
dampen it enough to solve the problem.
The real problem would be if 75ft is short enough for the Com speed, 9600 baud
should be ok, anything faster may run into
problems. Best to wire up a 75' spool of the Cat5 and check the communications
with a laptop or something before running the


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