RE: (ET) Oh yeah, serious ground fault

["Elie, Larry \(L.D.\)" <lelie ford com>]

Just for the info; all the tables of wire gauge and current are ignored in 
designing small equipment.  What is 
important is voltage drop (resistance based) on the wire.  The tables will 
tell you #10 is good to 30 amps; and 
that you need number 00 for 200 amps; that's true in your house where the 
runs are 50' long.  200 Amps on #10 
that is only a few feet long is NOT a big problem.  #10 has a resistance 
of .9988 ohms per 1000', so 5' is only 
5 mili-ohms.  #4 has a resistance of .2485 ohms per 1000', so 20' of 
number 4 (where my table ends) will have the 
same resistance AND TEMPERATURE RISE as 5' of #10.  Short is good.  The 
temperature of the wire depends on the 
resistance, current ambient temperature and duration; nothing more.  The 
starter leads on your car are probably 
#8 or at most #6; 500 amps for 1 minute is not uncommon.  The wires inside 
your alternator are no bigger than 
single strand #8 (and more likely #10) and we run them at up to 120 amps 
continuous (at 90 deg C...) because the 
net resistance is small.

Larry Elie


-----Original Message-----
From: elec-trak-bounces cosmos phy tufts edu
[mailto:elec-trak-bounces cosmos phy tufts edu]On Behalf Of Chris Zach
Sent: Saturday, July 31, 2004 3:11 PM
To: Elec-trak list
Subject: (ET) Oh yeah, serious ground fault


Okies. So I took the deck apart to find the source of half the ground 
fault on my E20. Didn't have to look far; when I took off the wire cover 
that runs along the length of the deck I found that the wire to the 
right motor was *cremated* along it's length.

To be honest, I have no clue how it stayed together. And it points out 
another design flaw on the Elec-Trak; the wires are not fused anywhere 
near their ratings. This is 10 gauge wire, and it's only protection is 
the 200amp main fuse links.

Ah well. I cut out the bad wire, re-wired with 10 gauge, and closed it 
up for now. Will have to go out and get some grommets to seal it all. 
However the tractor now runs totally normally.

Now for the fun part: There has to be a second ground fault on the 
tractor. In a main wire; it's got to be big enough to not have melted 
out under the current. I'll pull the resistor banks and start looking 
from there next weekend.

Chris


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