I went with two 3/4" pass-throughs, and that was sufficient (though a little tight) for my relatively simple build. This assumes you wrap each bundle with a section of fire sleeve that goes inside the fitting, which comprises as much volume as the bundle itself.
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Doug
RV-9A "slider"
Flew to Osh in 2017, 2018 & 2019!
Tail number N427DK
Donation made for 2020 You haven't seen a tree until you've seen its shadow from the sky -- Amelia Earhart
I have a full Dynon EMS setup and used two 1/2" or 5/8" conduit fittings. I had a third opening for the battery cable. I used BX fittings and the firesleeve goes on the outside.
Larry
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N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
I would recommend 3. It's easier to cover one up than to add more later IMHO.
Agreed. Once you get to the last 10% of the build, it's amazing the things you discover that need a wire or two going FFwd. I started out confidently with two penetrations; ended up with three.
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Terry Ruprecht
RV-9A Tip-up; IO-320 D2A
S. James cowl/plenum
(Dues paid thru Nov '18)