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Really dumb running wiring question I need to ask

Steve Crewdog

Steve Crewdog

Well Known Member
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I think it was Churchill who said It is better to keep your mouth shut and look like a fool than open it and prove it, but Churchill was a Lord of the Admiralty, not a kitplane builder.


I need to run some 20 ga power and ground wires to the master solenoid and starter contactor for a Rotax 914, the best way to support/run them is to lace them against the ground wire from the battery-engine. If the ground wire was a normal size 12-22 ga I don't think I'd have much qualms, but running them next to a 4 ga ground wire makes me wonder if it's a good idea. (I know, electrons can't pass though Tefzel. Can they?)

The battery ground runs aircraft left->right from the battery to the engine, the 20 ga wires run from aircraft left->right from the sources to the contactors.


Thoughts? Am I ok to do this, or should I find a different way to run them?


TIA
 

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bjdecker said:
Where's the bilge pump? ;)
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Under the fuel tank.


wirejock said:
I always hand twist power and ground for each device together then install. Keeps them electrons together. Probably doesn't make much difference. Old habit from radio days.
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I did that for a while, Larry, but it added bulk to the wiring harness, and when I messed up and had to undo/redo the wires they were kinked. Easier to keep them individual. Plus when they're twisted it's impossible to read a label in the middle of a run.
 
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I don't think that's what Churchill meant pretty sure he meant don't speak like a dumbass, asking questions is not speaking like a dumbass. Somebody wants told me think about what you're going to say before you say it that might be what Churchill meant
 
Is building the same airplane 3 times (do, redo, do again when you finally figure out how to do it.) the same as building 3 different airplanes? Then 5 years later looking at it again and going Hmmmmm..... Asking for a friend.


Probably one of the best things that happened to me during my build was having a retired USN Chief with 20+ years of working on airplane avionics stop by my hangar one day and started grilling me, finishing with "How are you going to repair this?" He's moved on now, but it meant the world to me when he'd stop by and make suggestions, or point to something and say "You need to work on this. Figure it out." Gradually they started turning to "Nice job. For a pilot."
 

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Twisting power and ground wires together is a good idea, presuming that all the ground current goes thru the wire and not thru the metal airframe in some fashion. In this case, the ground and power currents are equal and opposite, and there is a considerable reduction in any magnetic field created. So especially important around compasses, conventional or electronic.
 
I started using "Snake Skin" (https://buyheatshrink.com/) TechFlex product. Love it. Everything from now on goes in a "Bundle" of wires in snake skin; even 2 wires. Twisting is good if you are concerned w/ RF however it makes for more difficult to repair down line. If you R&R both twisted pair wires together, ok. R&R one of the twisted; not so good. All of your CAT5/CAT6e etc WIFI network wiring is twisted pair; important in that application.
I recommend put the two wires in a snake skin first then tie it to your 4GA Ground wire. Creates a separation...
IAW AC43.13.1B Section 11 this mostly answers your question of separation:


11-105. SYSTEM SEPARATION. Wires
of redundant aircraft systems should be routed
in separate bundles and through separate connectors to prevent a single fault from disabling
multiple systems. Wires not protected by a
circuit-protective device, such as a circuit
breaker or fuse, should be routed separately
from all other wiring. Power feeders from
separate sources should be routed in separate
bundles from each other and from other aircraft wiring, in order to prevent a single fault
from disabling more than one power source.
The ground wires from aircraft power sources
should be attached to the airframe at separate
points so that a single failure will not disable
multiple sources. Wiring that is part of electro-explosive subsystems, such as cartridge￾actuated fire extinguishers, rescue hoist shear,
and emergency jettison devices, should be
routed in shielded and jacketed twisted-pair
cables, shielded without discontinuities, and
kept separate from other wiring at connectors.
To facilitate identification of specific separated
system bundles, use of colored plastic cable
ties or lacing tape is allowed. During aircraft
maintenance, colored plastic cable straps or
lacing tape should be replaced with the same
type and color of tying materials.
 
Didn't need to lace it to the ground wire after all, but Thanks for the help, everyone.

As to Why it's taking so long to get OspRey flying, aside from some life events getting in the way, Kerry Fores wrote an excellent missive called Done, or done enough? that pretty much nailed it. Check it out: https://avbrief.com/done-or-done-enough/
 

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Twisting power and ground wires together makes it a joy to fix 50 years down the road when the insulation is worn through on the wires..... and they touch... and they are fished under panels that take all day to get off
 
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