Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Sat, 07 Sep 2002 19:05:32 -0400
Message-ID: <redirect-1723621@logan.com>
From: "Gary Casey" <glcasey@adelphia.net>
Subject: wire gage size and shielding
MIME-Version: 1.0
Content-Type: text/plain;
	charset="Windows-1252"
Content-Transfer-Encoding: 7bit
Importance: Normal

<<Small gage wire has been nothing but a problem to me.  I try never to go
below 18 AWG (stranded) because , with this size, the conductor itself
provides a measure of strain relief protection.  With smaller gage wiring,
termination becomes more and more of a  problem.  If you crimp the leads; as
in a connector, you have to be careful that the crimp doesn't sever the
conductors and there is always the stray-strand problem.    If you solder
the ends, then you introduce a solid  into a flexible conductor and
vibration can sever the conductors at the solder joint.

Yes, with larger conductors, the extra weight becomes a factor but I look at
it as insurance and cheap insurance at that.  So far, the wiring  for the
Storm-Scope, the Angle of Attack system, and the wiring for the MAC trim
system has given me many hours of problem chasing that can be attributed
directly to the use of small conductors.  I don't need problems like that.

As for shielding, yes, Yes, and YES.>>

I agree in general that "small" gage sizes may be more trouble than they are
worth.  However, automotive wires used to be limited to 18 gage or larger,
but now 20 gage is routinely used to save space and weight.  Good crimping
tools and connectors designed for that gage provide good mechanical
integrity.  Lots of aircraft wires are less than 20, but these are very
delicate and I plan to use mostly 20 gage.  Using excessively large wire can
also lead to fatigue failures where the wire has to bend.  We build the F-16
control sticks and it is amazing how many small wires are in the space
available.  They are reliable if done carefully.  That's why we get lots of
money for them.

We also reverse engineered the fuel probes and found the circuit design and
execution to be very crude.  There is no temperature compensation, linearity
compensation (not required anyway), no EMI protection and no environmental
protection.  I would certainly try to seal the wire entrance with RTV.
Theoretically, since it has a frequency, not analog output, shielding is not
necessary, but I agree with the previous post - shield it anyway.  You
certainly need to strain relief the wires close to the sensor.

Gary Casey
ES project