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  #1  
Old 12-06-2017, 10:20 PM
JDA_BTR JDA_BTR is offline
 
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Location: Baton Rouge, LA
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Default Cable Harness Length

I've got the position of all avionics components figured out in my panel. I'd like to build a harness based on measurements and bring it to the plane rather than wire it all on-site run by run.

I figured if I took all of the lengths, and added 12" I for sure would have enough run to each piece, allow for some extra when a component is pulled, and be able to take up any extra length with a double back, or loop, or whatever to mechanically make it fit.

Has anyone else done this? Is 12" a ridiculous add? I look at a lot of custom made harnesses and they don't try to get it exact. The approach fast stack for example seems to have runs of very generic length.
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  #2  
Old 12-06-2017, 11:40 PM
rvbuilder2002 rvbuilder2002 is offline
 
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All depends on your preference....

Other custom panel builders such as AFS and Steinair do panels with pre-planned routing for the main bulk of the harness which makes for a very tidy installation.
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  #3  
Old 12-07-2017, 05:43 AM
JDA_BTR JDA_BTR is offline
 
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Yes they do.... I like wiring things though, its the ham in me. Figure too long is way better than 1" too short, and service loops never hurt. I'll string some wires around the assembly and see what looks best....
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  #4  
Old 12-07-2017, 06:56 AM
jliltd jliltd is offline
 
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For simple installs I usually pull a string from start point to end point and mark the string with a Sharpie for any component locations or breakouts along the way. Then I can take the string to a long table and tape it down and label each end and each mark along the way.

The AEA puts on a great experimental avionics class that shows how to determine lengths and positions (3D) of components and then lay out a full-size harness bundle pattern on a table with masking tape. Each harness end point is labeled with connector type, wire spec and pin assignment referencing the component position on the opposite end of each wire. Then each individual wire or shielded multi-conductor wire is laid along its individual run tacked down by pieces masking tape until all the wires are in their place. Then the harness is completed by tying it neatly and professionally along its length with wax lacing tape (zip ties are amatuer and won't last like lacing). The harness and split out bundles come together on the table taking on the shape of the final harness in the airframe. Looks as good as factory harness. There are finer nuances such as whether to pin and install connectors on one end or both ends of each run prior to airframe install. And whether to pin at all on the far end so length can be finalized after running the harness. Etc.

That is only a small part of the excellent Avionics Installation for Experimental Aircraft training class at the AEA offered a couple of times a year. The emphasis is on the G3X, can bus, LRUs,appropriate shielding and methods, autopilot installation and set up (and first flight safety). I took the class a year ago and still refer to the excellent manual provided with my notes. I recommend the class for anybody with even the slighttest interest in wiring or avionics integration. Highly recommend.

Jim
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Last edited by jliltd : 12-07-2017 at 07:06 AM.
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  #5  
Old 12-07-2017, 07:03 AM
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rleffler rleffler is offline
 
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Quote:
Originally Posted by JDA_BTR View Post
I've got the position of all avionics components figured out in my panel. I'd like to build a harness based on measurements and bring it to the plane rather than wire it all on-site run by run.

I figured if I took all of the lengths, and added 12" I for sure would have enough run to each piece, allow for some extra when a component is pulled, and be able to take up any extra length with a double back, or loop, or whatever to mechanically make it fit.

Has anyone else done this? Is 12" a ridiculous add? I look at a lot of custom made harnesses and they don't try to get it exact. The approach fast stack for example seems to have runs of very generic length.
That's what I did and I regret not making them longer.

Think about this scenario. You want to make a modification and add a couple pins to a connector. Can you pull the tray out and lay it in your lap to work on (ideal situation).

When I had to modify the high density connectors on my 650, the slack that I had only allowed me to move the connector to about the rudder pedals. Having to work on the high density connectors in the foot well wearing bifocals is a major PITA.
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  #6  
Old 12-07-2017, 11:59 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Quote:
Originally Posted by JDA_BTR View Post
Yes they do.... I like wiring things though, its the ham in me. Figure too long is way better than 1" too short, and service loops never hurt. I'll string some wires around the assembly and see what looks best....
I wasn't suggesting just let the pros do it, just pointing out how the pros do it.

I don't think just adding 12" to your measurements would be a good idea.

Stringing some scrap wires and taping them together to mock-up exactly what you want (with service loops to meet your needs) is a good way to do it.
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