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From: A Jensen (no email)
Date: Sun Aug 01 2004 - 14:59:24 EDT
Having introduced the subject of SAE and AWG wire sizes let me add another
bit of information.
The heavy duty crimp lugs sold at my local marine outfiter are much thicker
than the plain copper lugs sold at the automotive supply store. The reason
is clear.
In automotve use a starter motor cable and its crimp lugs see intermitent
duty only when the start motor is cranking.
For boat battery application most of th etime this is th ehouse bank and it
can see sustained curent draw of 50 - 200 amps for hours on end.
Remember that a 2000 watt 12V inverte will draw 200 amps DC when running at
ful load.
That same inverter will charge at 100 - 120 Amps for hours when in bulk
mode.
As I mentioend previously, SAE wier sizes are 12% smaller than the same AWG
size.
Lugs made for SAE wiers have a corresponding reduction is size and current
carrying capacity.
When a conductor - wire or lug - is under sized, it generates some internal
heat while conducting current.
This heat causes the surface of the copper to oxidize ( we also call it
corrosion )
Tin is one of the few metals which does not oxidize as rapidly as stel or
copper.
Which is why tin is a preffered coating to reduce or eliminate rusting and
corrosion.
secondly, heavy wall crimp lugs stand up better to crimping because they
are stong enough to retain the crimped shape even when heated up and or
stressed by flexing.
Unfortunately they also require heavy duty crimp tools to properly crush
the sleve around the wiers and create a gas tight seal against the wires.
My crimp tool cost $200 as opposed to the cheap $25 tool used by many
automotive mechanics for making starter cables.
However my crimps will stand up to maximum curent draw 24/7 year after year.
Try that on a starter cable.
When a connector is heated up from high curent flow, the thin wall
automotive lugs will soften and may loosen their grip on the wire strands
whne compared to the heavy wall tinned lugs in such brand names as T$B,
Burndy, AMP and NEDCO to name some of the brands I have used. This is by no
means an exhaustive list.
I can get cheap 2/0 plain copper lugs from th eautomotive supplier for
fifty cents apiece.
In the Burndy, AMP or T&B brand name the same size lug cost $1.50
Which one would you rather trust to last 10 years or so without stating a
fier or leaving you without power?
And of course, since SAE wire is smaller than AWG wire the automotive lugs
have a smaller sleee hole and this won't always fit the larger and correct
size AWG cable.
LAstly, if you choose to use SAE wire instead of AWG, remember that the
ampacity tables are based on using AWG so now you are pushing the cable
beyond its allowablel limits.
For that mater how many of you derate the ampacity when the cable is used in
a hot engine room or when bundled together with more than two more current
carrying conductors in a tight wire chase?
Cheers
Arild
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