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allenmaris
Joined: 02 Sep 2020
Posts: 4
Location: Santa Ynez, CA
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 Posted: Sun Jan 30, 2022 10:38 am Post subject: Wiring Best Practices? |
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I’m designing the wiring for my RV-7A. I’ve been reading and looking at manufactures recommendations, Bob’s best practices, etc. Seems there are just not enough routes in the plane to keep so many wires separated as recommended by best practices. With 2 conduit routs down from the sub-panel to the floor of the plane, things are going to have to go into route 1 or route 2. I’m using shielded wire as recommended by manufacturers and keeping the UAT and the Com antenna runs apart from either other. But I still have to run the power wires for strobes, landing light, flaps, fuel pump, trim, etc. Where do I draw the line of “good enough”??
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Ceengland
Joined: 11 Oct 2020
Posts: 391
Location: MS
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| Posted: Sun Jan 30, 2022 11:01 am Post subject: Wiring Best Practices? |
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On 1/30/2022 12:37 PM, Allen Maris wrote:
| Quote: |
I’m designing the wiring for my RV-7A. I’ve been reading and looking at manufactures recommendations, Bob’s best practices, etc. Seems there are just not enough routes in the plane to keep so many wires separated as recommended by best practices. With 2 conduit routs down from the sub-panel to the floor of the plane, things are going to have to go into route 1 or route 2. I’m using shielded wire as recommended by manufacturers and keeping the UAT and the Com antenna runs apart from either other. But I still have to run the power wires for strobes, landing light, flaps, fuel pump, trim, etc. Where do I draw the line of “good enough”??
My understanding is that with few exceptions, grounding practices are
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far more critical than adjacent wires. The UAT & comm *antennas* might
need some separation, but properly terminated shields on quality coax
should prevent any issues with the wires themselves.
Which combinations are most concerning to you?
Charlie
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allenmaris
Joined: 02 Sep 2020
Posts: 4
Location: Santa Ynez, CA
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| Posted: Sun Jan 30, 2022 11:30 am Post subject: Re: Wiring Best Practices? |
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| Ceengland wrote: | On 1/30/2022 12:37 PM, Allen Maris wrote:
My understanding is that with few exceptions, grounding practices are
far more critical than adjacent wires. The UAT & comm *antennas* might
need some separation, but properly terminated shields on quality coax
should prevent any issues with the wires themselves.
Which combinations are most concerning to you?
Charlie
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Hi Charlie, the biggest ones I've written down from various sources:
•Keep some separation between strobe lines and any audio wires, coax or headset jacks. I HAVE to run this next to some coax, and the UAT seems like a better option just to avoid any possible audio feedback on the Comm frequency which I might hear.
•Separate UAT and Comm coax (I can do that)
•Avionics/Audio wiring shouldn't share bundles with power distro lines (assuming this means the big battery/Alternator connections and not just standard device power)
•Keep Can Bus wires away from power/ground lines, especially pertaining to loads for motors.
I know some of this is ideal/best-case scenario, I just don't have enough experience to know where that line is. All I remember is the days of installing car stereos in my cars when I was younger and hearing the telltale hum of a poor install!
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nuckolls.bob(at)aeroelect
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| Posted: Sun Jan 30, 2022 11:59 am Post subject: Wiring Best Practices? |
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At 01:06 PM 1/30/2022, you wrote:
--> AeroElectric-List message posted by: Charlie England <ceengland7(at)gmail.com>
On 1/30/2022 12:37 PM, Allen Maris wrote:
--> AeroElectric-List message posted by: Allen Maris <allenmaris(at)gmail.com>
I'm designing the wiring for my RV-7A. I've been reading and looking at manufactures recommendations, Bob's best practices, etc. Seems there are just not enough routes in the plane to keep so many wires separated as recommended by best practices. With 2 conduit routs down from the sub-panel to the floor of the plane, things are going to have to go into route 1 or route 2. I'm using shielded wire as recommended by manufacturers and keeping the UAT and the Com antenna runs apart from either other. But I still have to run the power wires for strobes, landing light, flaps, fuel pump, trim, etc. Where do I draw the line of good enough??
My understanding is that with few exceptions,
grounding practices are far more critical than
adjacent wires. The UAT & comm *antennas* might
need some separation, but properly terminated
shields on quality coax should prevent any issues
with the wires themselves.
Which combinations are most concerning to you?
Charlie
Exactly!
It's my suspicion that authors for 'best practices' in wire
routing have not spent much time working with the heavy iron
birds . . . I worked for every airframe manufacturer in Wichita
at least once . . . one of them three times. In 40+ years
I can recall but a couple of times that stimulus coupled
between a 'victim' and 'antagonist' was initially attributed
to 'poor separation of wiring'.
A couple of stand-out incidences included a recovery parachute
system that spontaneously launched from the tail of an airplane.
The event was first blamed on lack of shielding and/or separation
of critical wires from potential antagonists.
The second was at Beech on a Hawker 800 where a host of warning
annunciators were triggered by the energizing of a 400Hz, AC
blower motor in aft cabin.
In BOTH cases I discovered effects of poor grounding practice.
The blower took a SINGLE power wire through the ship's wire
bundle tunnels and GROUNDED the motor at the tail of the airplane.
This turned that wire into the primary winding of a TRANSFORMER
that was relatively tightly coupled to lots of other wires. In
the first case, the designers routed SINGLE conductor firing signals
from the control panel to explosive devices in the parachute system
and grounded those initiators in the tail. To complete the
design guaranteed to fail, they grounded the source end of those
same wires in the control panel . . . ostensibly to reduce the
possibility of introducing hazardous stray signals into the
firing lines. This guaranteed that those feeders combined with
voltages induced in the fuselage to set up a low impedance
source of extraneous energy that simultaneously lit up every
initiator in the system. It was later deduced that the airplane
had flown past a active thunderstorm and while there was
separation of sufficient miles for safe flight, it was probably
a lightning strike that provided the PRIMARY energy source
for initiating the event.
This was one of a couple reasons that yours truly was assigned
the task of designing and constructing the last four recovery
parachute systems installed in Beech flight test aircraft before
my retirement. The other reason was that our original contracted
supplier of a control system for the parachute on the Premier I
blew off a couple hundred thousand dollars and two years of
development time before delivering a system that launched the 'chute
in the hangar.
A long time friend and colleague Dean Matson and I along with
the capable hammer-n-tongs guys in the Beech Targets Division
designed, built and qualified a system from scratch in about
30 days for a budget of well under $20K.
There were no doubt others but I'd have to stir the memory
pot for awhile to dig them up. Bottom line is that ROUTING
of wires in community of systems where proper attention is
given to GROUND LOOPS is not an issue. In fact, there are rigorous
qualification tests for all appliances designed for TC aircraft
that makes sure that appliances will be peaceful and
harmonious citizens of the aircraft.
While at Lear working on the GP180 program, I witnessed first
hand the battles between hydraulics, controls, fuel, wire
slingers and HVAC guys for space in the aircraft. Anyone
who complained about proximity of his hardware with any
other might well find his car covered ten or so rolls
of soggy toilet paper when he got of work that day.
Don't worry about HOW wires are routed and bundled. If you've
paid attention to good GROUNDING practices and particularly
good assembly practices for coax connectors, you stand a much
better chance of being brought down by a meteor strike than by
an altercation between electro-whizzies in the airplane.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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Ceengland
Joined: 11 Oct 2020
Posts: 391
Location: MS
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| Posted: Sun Jan 30, 2022 12:03 pm Post subject: Wiring Best Practices? |
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On Sun, Jan 30, 2022 at 1:35 PM allenmaris <allenmaris(at)gmail.com> wrote:
| Quote: |
allenmaris(at)gmail.com>
Ceengland wrote:
> On 1/30/2022 12:37 PM, Allen Maris wrote:
>
> >
> >
>
> My understanding is that with few exceptions, grounding practices are
> far more critical than adjacent wires. The UAT & comm *antennas* might
> need some separation, but properly terminated shields on quality coax
> should prevent any issues with the wires themselves.
>
> Which combinations are most concerning to you?
>
> Charlie
>
Hi Charlie, the biggest ones I've written down from various sources:
•Keep some separation between strobe lines and any audio wires, coax or
headset jacks. I HAVE to run this next to some coax, and the UAT seems like
a better option just to avoid any possible audio feedback on the Comm
frequency which I might hear.
•Separate UAT and Comm coax (I can do that)
•Avionics/Audio wiring shouldn't share bundles with power distro lines
(assuming this means the big battery/Alternator connections and not just
standard device power)
•Keep Can Bus wires away from power/ground lines, especially pertaining to
loads for motors.
I know some of this is ideal/best-case scenario, I just don't have enough
experience to know where that line is. All I remember is the days of
installing car stereos in my cars when I was younger and hearing the
telltale hum of a poor install!
I'll defer to Bob for 'final answers', but...
Strobes *can* be problematic, but don't have to be. Traditional strobe
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issues can be minimized a bit with 'home run' grounds and proper
shields/terminations per mfgr specs. I had an RV with the 'whoop whoop' of
its strobe in the intercom, and it was about 99% related to the ground
location (locally grounded) of the strobe power pack. The charge/discharge
power variations were riding on the ground path of the audio system. (I
didn't wire the a/c.) LED strobe noise can be minimized by using properly
filtered LED drivers (and good grounding practices).
My UAT experience is limited to the uAvionix, and all its components are in
the wingtip as recommended by one of their engineers. The power supply to
the assembly runs in bundles with everything else in the plane. This one is
an RV6 (again, I didn't do the initial wiring), and all the wires
(including xpndr & comm coax) leaving the panel go down the center support
in two fat bundles, and then through the spar and fan out to their
destinations throughout the airframe. No noise in this installation.
Avionics/audio: Again, grounding practices predominate. If it's convenient
to keep the mic lines at least a few inches away from the 'fat' power
wires, why not? But for most installs, you'd have to try to get them close,
anyway. Keeping audio grounds isolated from airframe grounds and tying them
directly to the audio panel/intercom as shown by the mfgr will almost
always have more effect than any 'adjacency'. What risk there is of
electromagnetic noise introduction can be minimized by using twisted pairs
for the audio, and minimizing to the degree that's practical, the length of
the adjacency. Crossing at close to 90 degrees doesn't hurt anything at all
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Charlie |
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user9253
Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan
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| Posted: Sun Jan 30, 2022 12:23 pm Post subject: Re: Wiring Best Practices? |
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Mount headset jacks with insulating washers to be sure that they are not grounded locally. (They will be grounded at the instrument panel end)
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Run power and ground wires as a twisted pair for electrically noisy devices.
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A very knowledgeable person once wrote: If cables are modern coax (RG400 or RG142), you can run them right together with any wires in any system.
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Joe Gores |
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allenmaris
Joined: 02 Sep 2020
Posts: 4
Location: Santa Ynez, CA
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| Posted: Mon Jan 31, 2022 11:40 am Post subject: Re: Wiring Best Practices? |
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Thank you all for the input and the story, Bob. I am using best practices for shielding/grounds to the best of the common theories that I've come across from multiple sources. It was the best practices from one source but no mention from another source that had me thrown. I'm feeling much more confident that I'll probably be fine. And for sure, pushing the PTT button won't fire the ejector seat.
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Mon Jan 31, 2022 2:45 pm Post subject: Wiring Best Practices? |
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At 01:40 PM 1/31/2022, you wrote:
| Quote: | --> AeroElectric-List message posted by: "allenmaris" <allenmaris(at)gmail.com>
Thank you all for the input and the story, Bob. I am using best practices for shielding/grounds to the best of the common theories that I've come across from multiple sources. It was the best practices from one source but no mention from another source that had me thrown. I'm feeling much more confident that I'll probably be fine. And for sure, pushing the PTT button won't fire the ejector seat.
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About those shields . . . the most mis-understood feature
in systems interfacing: Follow them manufacturer's
recommendations when given in the installation manual.
SOMETIMES the shield is BOTH a mitigator of noise propagation
AND conductor of energy. I have purposely used shielded wire
as the power feeder for LED indicator lights meaning that
both center conductor and shield need to be 'powered'.
But shields in small signal and data systems are USUALLY
intended only to mitigate ELECTRO-STATICALLY coupling between
adjacent wires in a bundle. In these cases, no substantial
energy is conducted on the shield and only one end is
'grounded'. In rare cases, builders have mistakenly
deduced, 'if one ground is good, two grounds are better'
only to find that a new, magnetically coupled noise has
appeared in the victimized system due to ground loop
currents flowing on the shield.
Confucius says, "When in doubt, read the instructions.
If still in doubt, check it out on the AeroElectric-List."
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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