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Re: (ET) Oh yeah, serious ground fault - connectors
To add a bit to what Larry said,
Clean, uncorroded connections are extremely important, after you pick your
new wire size.
So, tinned wire, crimped & soldered connectors, and anti-corrosion compound
are often essential.
In the case of these machines, plastic 'grommet' strip (applied to the
edges
of the holes in the chassis that the wire feeds through), or that
corrugated
plastic tubing (split loom?) over the wire, is helpful in preventing
abrasion of the wire's insulation. Unfortunately these might not prevent
some problems like Chris had, when the wire melted from the inside out -
depending on the temperature rating, the tubing could prevent two wires
from
melting together.
John
----- Original Message -----
From: "Elie, Larry (L.D.)" <lelie ford com>
To: "Chris Zach" <czach computer org>; "Elec-trak list"
<elec-trak cosmos phy tufts edu>
Sent: Monday, August 02, 2004 10:06 AM
Subject: RE: (ET) Oh yeah, serious ground fault
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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