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What Size Plastic Bushing For a Bundle of 44 Wires?

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David Paule

Well Known Member
That's the question. This is for an RV-3B which has a very small cockpit. I was amazed to realize just how many wires there were.

I've got a variety of things feeding up to the avionics panel, and they've got to pass through a bushing into the spar bulkhead's aft side. All together these are for a transponder remote box, an ADAHRS, a couple of autopilot servos, the lights, the headphone plugs and so on. After they've made it into the side of the bulkhead, they'll go to the avionics shelf.

I think the biggest wire is probably an 18 ga., but that's still slightly TBD so far. I think that there are a few shielded cables in the mix. There are no antenna cables in the bundle.

I'm putting together the armrest assembly on that side of this small RV-3B cockpit and the bundle will go into the side of the spar bulkhead below the armrest's bottom shelf, where there's not a lot of room.

Thanks!

Dave
 
C'mon, you guys, you're pulling my chain here - I need to drill for the proper size SB plastic bushing.

Let's forget about the alligator grommet and the caterpillar grommet and the centipede grommet. Please, no more of that creepy crawly chewy stuff.

Thanks,
Dave
 
Gather up a bunch of wire until you have 44 pieces.

Measure it???

Really, it is hard to give an exact size without knowing what you are putting in there.

You say most likely 18 for the largest, but what about the other 40+ wires?
 
Inside Diameter required ?

Wrap a tie wrap around the 44 bundle. Measure the nominal OD. Text me the number and I will make you a flanged Delrin bushing with OD that matches common drill sizes.
 
Calc'd size

I did a rough calc using Pi R squared assuming wire diameters of 2mm for the 44 wires and the bundle should theoretically fit through a 1/2" hole, just. If you went one size up it would be easier to get any pins and labels fed through. Disclaimer: 2mm is just a guesstimate for the wire.
 
Thanks to several of you, especially Larry. I bundled about 45 wires and Paul, you're right - they fit in a 1/2" bushing, without a lot of margin. I decided to use the next size larger, the SB750-10, which has enough room for anything that I might not have accounted for so far.

So thanks, one and all, even for the earlier entertainment.

Dave
 
Oh yes.

I'd been hoping that someone ahead of me might have had some experience to share and be able to just tell me the answer.

Dave
 
Hey David - since you don’t have the bundles fully defined, you already know the answer - you want to put the largest hole that the structure (and edge distance) will allow, since wiring always grows to fill available space…..and you know that I have BTDT with a -3B…..

Paul
 
If the wiring gets out of control, I'll start removing things. The first to go will be the autopilot servos.

Dave
 
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