Firewall passthrough failure

[BJohnson]

The drawings show a firewall pass through for the main bus power, starter contactor, battery contactor, etc that is comprised of two plastic snap bushings pressed (an SB625-8 and SB500-6) together in a hole in the firewall. I installed this per plans, but contemplating failure modes raises a question.

Has anyone experienced a failure of this design? It seems likely that the thin firewall will eventually saw through the plastic bushings and then into the wire insulation.

I followed the aeroelectric schematic Z11 which has a 6 awg wire leading from the battery contactor to the main bus un-protected. A direct short of the 6 awg wire to the firewall, with no circuit protection, would make things pretty exciting.

I am aware of the various other pass throughs available, but my question is about the durability of the "per plans" version.

[alpinelakespilot2000]

Hi Brice-

Put an aluminum doubler on the aft side of the firewall wherever you want a pass through with a bushing. Shouldn't have any problem if you do that. FWIW, I only used the double bushing methods for the control cables where a little bit of flex helped with routing (and where you needed to split the bushings to fit over the cables). For wires I used the single smallest bushing I could, unsplit, to hold any wires tight so that there would not be any relative movement between wires, bushings, firewall holes and their associated doublers. Used CS1900 over everything topped off by stainless steel grommet shields.

Not a full answer to your specific question, but hope it helps.