In order to tidy up the spag,
and perhaps improve the radio performance, I wondered if I was to organise the
ground points and have the electrical services grounded to a common point and
the avionics to a separate common point.
Dom,
What you want to avoid is multiple grounding points
that are interconnected through multiple paths. I would recommend a single
heavy duty ground point on the firewall that the large cable from the negative
battery terminal attaches to. The battery negative lead should be at
least #4 cable as it will carry the current from the starter back to the
battery. Typically the ground point on the firewall is a stud
that goes through the firewall to provide a grounding point for things under the
cowl, like the starter. Unless the manufacturer recommends otherwise I
would not ground engine sensors (fuel flow, fuel pressure, oil pressure) to this
point. I would route them with the other wires from the sensors to the
engine interface box.
Behind the panel I would run the ground
wires from the avionics, and whatever else is currently
grounded behind the panel, to a single ground bus. You can buy
grounding busses or make one from a bar of copper or brass. I would then
run a single heavy wire, #10 or #8, from that ground bus to the ground stud on
the firewall. (You could run it all the way to battery instead but that's
probably overkill.) If you have more than one grounding bus run a heavy
wire from each bus to the common ground point. Don't daisy-chain grounding
points. When you're done there should be a single wire from each grounding
bus, if you have more than one, to the common ground point and no wires running
between grounding busses.
For audio wiring follow the audio panel
manufacturer's instructions. Typically this involves using a shielded
multiconductor cable from each audio source, or destination, to a channel
on the audio panel. Most manufacturers then recommend grounding the shield
at the audio panel only. Again, follow the manufacturer's instructions on
how to terminate the shields. If this requires soldering wires to the
shield that are then tied to the connector backshell or the audio panel chassis,
keep these wires as short as possible. Never use the cable shield as a
return. For example a standared stereo headset jack will have a wire for
left audio, one for right audio, and one for return. In this case you
would use 3-conductor cable. Do not use 2-conductor and then cheat and use
the shield for a return.
If I've made an error in my descriptions I'm sure
someone will bring it to my attention.
Tom Gourley
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