[8023-POEP] Cabling and wire current capacities
As I stated I would
do, here is information I have on the cabling and wire current capacities. I
scanned in some documents and, fortunately, found the complete NASA related
document. I cannot attach the files to this email because the
server limits to 100K of attachments. However, those that would like the files I
will be glad to forward upon request.
The key document is
the MIL-W-5088K. This document has been transferred to SAE control under
standard AS50881. The SAE web site has a cost of this document, non-member, of
$59. Maybe someone on this list has this copy or can obtain it to share with the
list.
The NASA TM102179
document discusses the cabling design for space payloads. I feel this would be
the best starting point.
Surprenant is a
cabling company that has some data on cabling derating. But their ampacity chart
starts at 18 AWG and goes up from there.
A fusing current
document was passed to me, years ago, from a line of engineers and is more
of an eye-opener. The fusing current for 26 AWG wire is 20.5 A. Quite a bit to
look at, but clearly unreasonable.
Looking at the NASA
document (referenced above) and running the numbers for 100% wire usage, 50 F
temp rise we would get a maximum current loading of 3.588 A per wire. (A 4.46V
drop based on 2-pair conduction for 100 m)
This is very large
and would put a maximum limit on the power. This does not take into account for
voltage drop along the cable.
A bit more searching
brought up the following website
This states that 26 AWG wire can handle up
to 2.2 A for chassis wiring and 0.361 A for power wiring. These currents relate
to a voltage drop of 2.74 V and 0.45 V for 2-pair conduction for 100
m.
If we look at any
baseline for current in the wire. I would say the 0.361 would be a good start.
Then add on upping the voltage to 55 V, we can see about 39 W on the PD
side.
Derek Koonce
Architect, Standard Product Group
JSI Microelectronics
4235 Forcum Ave., Ste. 500
McClellan, CA 95652
916-648-2089 x114