Interesting day today, lots of smoke in the cockpit!
So while doing a small panel upgrade for a customer I had a bit a meltdown on his aircraft. The panel mounted Lightspeed CB, with open and bare terminals was connected directly to the battery, and was located right under the xpdr rack I was replacing (within about 1/8"). Well as soon as the rack came loose it came into contact the uninsulated terminals. (of course I was unaware at the time that this situation existed with a hot bus right below the rack).
I can tell you this, there was a ton of smoke accompanied by some small flames as the wiring began to burn, disintigrate and melt. All the switches and master were off so there was no killing this thing and it just continued to burn until the wiring finally burnt thru. I was scrambling to get the cowl off so I could disconnect the battery, but by the time I got if off the wires has already burnt thru and opened up.
So whats the moral to this story, do not run 'HOT' unprotected (no fuse, CB, contactor controlled) wires into the cockpit. This situation could have easily presented itself from any number of causes (loose hardware, wires, breaker, switches getting loose etc.) If this would have happened in flight there was no way to kill power to the burning wires, and trust me with a closed canopy you would be in serious trouble fast. I was really pretty amazed at how much smoke there was, in the air this likely would have ended badly.
For your Hot battery busses (this includes battery charger pig tails) there should ALWAYS be a fuse (or some type of circuit protection) located at the battery to prevent this kind of thing from happening.
Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
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RV7A built 2004, 2000+ hrs, New Titan IO-370, Bendix Mags, MTV-9 prop
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Last edited by Walt : 04-16-2018 at 08:44 PM.