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Wire Choice?

CJK

Well Known Member
I'm still quite early in my build, but not too far down the road is installation of the elevator trim servo and the tail strobe/position light. I've read several threads here where folks talk about using different wiring from that supplied with the kit (and don't worry, I'm definitely using different connectors!), but I've grown increasingly confused as to what to choose as a replacement. :confused:

Can anyone make some recommendations -- with explanations, please! -- as to the best wire/cable to use for these two applications?
 
You want durable, flexible and easy to install.
- Elevator trim: Single four #22 conductor shielded wire. Two conductors to power the trim motor, one for servo position voltage, one for servo position sense, shield for ground.
- Tail nav/strobe (assuming you are using LED): Single three conductor #20 shielded wire. One conductor for nav power, one for strobe power, one for strobe sync, shield for common ground.

These shielded cables are available from Stein.

Carl
 
You want durable, flexible and easy to install.
- Elevator trim: Single four #22 conductor shielded wire. Two conductors to power the trim motor, one for servo position voltage, one for servo position sense, shield for ground.
- Tail nav/strobe (assuming you are using LED): Single three conductor #20 shielded wire. One conductor for nav power, one for strobe power, one for strobe sync, shield for common ground.

These shielded cables are available from Stein.

Carl

Is it normal to use the shield like this to actually carry power?

I used this for my trim even though it’s not shielded - hope I don’t regret that later, if I end up with a Garmin servo. https://www.steinair.com/product/24-ga-5-conductor-trim-wire-jacketed/
 
Cable Shields As Power Wires

Is it normal to use the shield like this to actually carry power?

While you may be able to get away with using the shield as the return leg (ground) for the nav/strobe lights, I wouldn't recommend it. The shield is meant in most cases to prevent the transmission of EMI/RFI between cables and other sensitive devices.

When powering a pulsing power device such as a strobe, the EMI/RFI is typically higher and can cause interference with other devices in your aircraft such as radio reception and other sensitive low voltage electronics such as magnetometers.

On my aircraft I carried a separate return/ground conductor back to the ground block inside of the shield, and terminated the shield separately. Upon completion of my RV-10 avionics systems, I had zero noise or interference issues.

While this adds a little bit to the cost of the cable, and requires additional terminations, it is in my opinion a preferred method. As a registered professional electrical engineer with a degree in electronics engineering and significant experience in industrial control system design and construction, that would be my recommendation. But as the builder, it is of course your decision.

Regards,
 
If you are going Garmin it's recommended that you use a 2 cond/shielded (22ga) wire from the servo to the trim motor, Garmin uses PWM from the servo to control trim motor speed and therefore is subject to emitting noise.
 
Thanks, guys -- very helpful info!

Based on the recommendations above, I'll likely run a 20-4 cable for the tail strobe/position light. (And yes, it's an LED: AeroLEDs SunTail.)

I'm a little confused about the wiring of the elevator trim motor, though. I'm definitely going with a Garmin panel and AP servos, so I'll need to run the 2 conductor cable Walt mentioned from the pitch servo to the trim motor. But do I ALSO need to run the 22-4 cable that Carl described? Or does the connection from the Garmin servo replace the 2 power conductors to the servo?
 
Thanks, guys -- very helpful info!

Based on the recommendations above, I'll likely run a 20-4 cable for the tail strobe/position light. (And yes, it's an LED: AeroLEDs SunTail.)

I'm a little confused about the wiring of the elevator trim motor, though. I'm definitely going with a Garmin panel and AP servos, so I'll need to run the 2 conductor cable Walt mentioned from the pitch servo to the trim motor. But do I ALSO need to run the 22-4 cable that Carl described? Or does the connection from the Garmin servo replace the 2 power conductors to the servo?

If I were running my tail wires again (I just might!) then I would run a shielded 2 core 22awg for power and a 3 conductor jacketed for the trim position. For a couple of reasons - one is to shield the power wires, but the other is they end up going to 2 different boxes in the end so would be better as seperate cables. As it stands for me now, where my 5 conductor goes past the Garmin servo I will need to break the 2 power wires and route them to and from the servo. Then the length of wire from the servo to the trim servo is unshielded - but that’s the way the factory harness runs so I’m hoping it’s fine.
 
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If I were running my tail wires again (I just might!) then I would run a shielded 2 core 22awg for power and a 3 conductor jacketed for the trim position. For a couple of reasons - one is to shield the power wires, but the other is they end up going to 2 different boxes in the end so would be better as seperate cables. As it stands for me now, where my 5 conductor goes past the Garmin servo I will need to break the 2 power wires and route them to and from the servo. Then the length of wire from the servo to the trim servo is unshielded - but that’s the way the factory harness runs so I’m hoping it’s fine.

As Trent above mentions, a 3 wire to the GEA24 from the Ray Allen servo for position. and a separate shielded 2 cond from Garmin servo to trim motor.
Std 22 single conductor from trim relays to Garmin servo trim input.

Follow the recommended light wiring for nav/str.

I'm doing a wiring job on a 14/Garmin, not using any of Van's harnesses.
 
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...and

"... As a registered professional electrical engineer with a degree in electronics engineering and significant experience in industrial control system design and construction, that would be my recommendation. But as the builder, it is of course your decision..."

You may want to let AeroLEDs in on it because their installation instruction specify using the shield.

I wired my RV-10 per their recommendations and I have no avionics noise whatsoever...
 
You may want to let AeroLEDs in on it because their installation instruction specify using the shield.

I wired my RV-10 per their recommendations and I have no avionics noise whatsoever...

Yes. I saw where AeroLEDs changed that. Originally they didn't specify to use shield as ground but about 3 or 4 years ago they changed to that. I think they go so far as to say that using the shield for ground is less noisy than having the ground inside as a standard circuit where we leave the shield for pure shielding. That got my attention as I too am an electrical engineer (and aerospace engineer). I have done it both ways, the earlier installs with dedicated ground separate from shield and then switching to the shield ground configuration. I haven't noticed a difference as both are quiet but if AeroLEDs suggests the best way and it's lighter who am I to argue?

AeroLEDs are still my all-around favorite strobe product line.

Jim
 
As Trent above mentions, a 3 wire to the GEA24 from the Ray Allen servo for position. and a separate shielded 2 cond from Garmin servo to trim motor.
Std 22 single conductor from trim relays to Garmin servo trim input.

Follow the recommended light wiring for nav/str.

I'm doing a wiring job on a 14/Garmin, not using any of Van's harnesses.

Sorry for digging up an old thread. I'd like to understand better when one would and wouldn't use shielded:

Why should the servo to trim power be shielded, but the relay to servo trim input can be unshielded? Can the servo power leads also be unshielded? I ask because the power going into the servo from the relays would throw off as much, if not more, electronic interference than the servo to trim leads, all while passing near and alongside a whole lot more wires and components.
 
Sorry for digging up an old thread. I'd like to understand better when one would and wouldn't use shielded:

Why should the servo to trim power be shielded, but the relay to servo trim input can be unshielded? Can the servo power leads also be unshielded? I ask because the power going into the servo from the relays would throw off as much, if not more, electronic interference than the servo to trim leads, all while passing near and alongside a whole lot more wires and components.

There is no electrical reason to use shielded cable for trim servos - but that is what I use. As I mentioned, a single, four #22 conductor shielded cable has all the wires you need, and the single cable provides for a much more durable wire run than a bunch of individual wires.

For LED strobes, the three #20 conductor shielded cable as I mentioned does what you need, as well as provides a little protection agains RFI.

This has worked well for me on three RVs.

Carl
 
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