with the magneto wires but I don't have magnetos. Bob Knuckoll's book
has a good discussion on noise propagation from wires but you knew I was
going to say that ;)
After a wee bit of investigating I put everything through the same hole.
For wires that are paired (signal plus ground) I also ran the ground
through the same hole and then grounded everything at the same place
behind the firewall. I don't think that is required but it seemed like a
good idea especially for moderately high current digital signals like
the connections to the ignition coils and injectors.
And of course all the very low level alternating signals (crankshaft and
camshaft sensors) are also shielded with the shield grounded at the
computer end only. Again probably not required but it seemed reasonable
and the car was wired similarly. I suspect my biggest risk is noise from
my alternator feed because my batteries are also behind the firewall.
I believe it is good practice to ground everything to the same point to
eliminate ground loops, noises, and interference. Ground loops occur
when two systems share the same ground. For instance I am grounding my
strobe power supplies to the wing spar at the wing tip. Now if I also
ground my headset or microphone jack to the airframe then I would expect
to hear a noise everytime my strobes fire as the voltage at the headset
ground point would rise a bit everytime the strobes fire. When current
flows there is always a voltage drop associated and that is also true
for current flowing through the airframe. So isolate the headset jacks
from the airframe and run that ground back to a common point on the
firewall and no ground loop noise. I have about 40 ground wires going to
push on tabs on the firewall.
Ken
Kim Kimball wrote:
I am hoping to finish the wiring that must pass through the firewall this weekend. I wonder if there are any no-nos in grouping certain types of wires. I've got power, electronic ignition, IVO prop control and sensor wires, and engine gauge sensor wires that need to pass through the firewall. Can all of these types of wires be grouped in the same feedthrough?
Mike
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