cable sizing [RE-wrenches]

David Palumbo, Independent Power & Light ipl at sover.net
Tue Sep 4 18:53:03 PDT 2001


Question on inverter cable sizing for large system: 127 kwhr battery bank,
(2) 3k hydro turbines (Ron MacLeod's),
Over 4k of pv to be added next year, (2) Trace SW4548E's with DC175A
Heinemann's.
According to my wire loss calcs, and Bill Miller's Excel spread sheet, The
gain in going with 4/0 cables (2 pairs) seems very small even when figuring
for worst case.
Using a low voltage of 44vdc and using a high current of 150 Amps at 28' one
way wire length it comes out to 1.85% Voltage drop with 2/0 and 1.16% using
4/0. If it was going into my home I would not hesitate using the 2/0 because
I would feel that using the extra copper was a waste of resources and cash.
But it is for a customer  and of course we want to do the right thing for
all concerned here also but the problem is the Trace Manual says to use 4/0
for SW4548's at 5' to 10' of one way wire run.
This appears to be overly conservative. Checking the numbers on their chart
for SW4024's I come up with a Trace recommended
2.07% Voltage drop for a 14' wire run at 22vdc and 267 Amps.
So my question is why is 2.07% VD fine for the SW4024 but a lower (1.85%)
Voltage Drop is not OK for the SW4548?

Am I missing something here? I really don't want to use unnecessary Copper.

Dave Palumbo

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