From a previous thread...
...which is a very good point.
That inexperienced builder may wish to learn more. Like most issues, God is in the details.
At typical operating temperatures the snap bushings will be fine.
Snap bushings combined with a good sealant choice actually performed at a reasonable level in a fire resistance test, maintaining a gas tight seal for roughly 1-1/2 minutes when adjacent to, but not encompassed by the hot spot. That said, sealant choice is an integral part of bushing performance, and there were significant differences in sealant. The popular orange Permatex was not a good choice, as it appeared to be highly flammable, and would serve as a fire transfer mechanism, bringing open flame and smoke to the cabin side.
In the same hot test, a simple tubular pass through filled with intumescent sealant performed much better than the basic snap bushing and sealant. It never lost a gas tight seal, even when subjected to the full 2000F, and did not itself transfer flame to the cabin side. The test was ended when the cabin side tefzel wire insulation ignited via its red hot copper core.
The popular eyeball style pass throughs were not tested, but their performance is going to be predictable. Aluminum eyeballs should be expected to melt if encompassed in the hot spot, but maintain integrity if held below 1000F, more or less. Steel eyeballs would maintain integrity regardless, but may not remain gas tight when the wire insulation melts.
Read here:
https://vansairforce.net/community/showpost.php?p=549778&postcount=38
https://vansairforce.net/community/showpost.php?p=549798&postcount=40
https://vansairforce.net/community/showpost.php?p=549839&postcount=42
"...Yes Mickey, I constantly come across RVs that have firewall penetrations made with nylon snap bushings covered with a blob of "high temperature" red RTV such as Permatex Silicon Gasket Maker or similar. This is crazy..."
I guess you ought to address this with Vans. Referring to RV-10 plans, section OP37-2 figure 1, electrical harness, Vans says drill a 1/2" hole for firewall penetration of the battery cable and use a SB500-6 snap bushing...
It may not be what YOU consider airworthy, quality, or whatever you want to call it but it is spelled out in the plans that way. Someone with little or no experience in this hobby is going to follow the plans...
...which is a very good point.
That inexperienced builder may wish to learn more. Like most issues, God is in the details.
At typical operating temperatures the snap bushings will be fine.
Snap bushings combined with a good sealant choice actually performed at a reasonable level in a fire resistance test, maintaining a gas tight seal for roughly 1-1/2 minutes when adjacent to, but not encompassed by the hot spot. That said, sealant choice is an integral part of bushing performance, and there were significant differences in sealant. The popular orange Permatex was not a good choice, as it appeared to be highly flammable, and would serve as a fire transfer mechanism, bringing open flame and smoke to the cabin side.
In the same hot test, a simple tubular pass through filled with intumescent sealant performed much better than the basic snap bushing and sealant. It never lost a gas tight seal, even when subjected to the full 2000F, and did not itself transfer flame to the cabin side. The test was ended when the cabin side tefzel wire insulation ignited via its red hot copper core.
The popular eyeball style pass throughs were not tested, but their performance is going to be predictable. Aluminum eyeballs should be expected to melt if encompassed in the hot spot, but maintain integrity if held below 1000F, more or less. Steel eyeballs would maintain integrity regardless, but may not remain gas tight when the wire insulation melts.
Read here:
https://vansairforce.net/community/showpost.php?p=549778&postcount=38
https://vansairforce.net/community/showpost.php?p=549798&postcount=40
https://vansairforce.net/community/showpost.php?p=549839&postcount=42