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Circuit Protection of Main Batery - Starter Wire

G

gkochers

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I thought I had a pretty good plan for wiring, based mostly on Z-13. I'm starting to run some actual wires before sealing up the baggage floor and I've realized that no wiring diagram I have ever seen shows any sort of circuit protection (fuses) to protect the #2 wire running from the battery, through the master contactor, to the starter contactor, to the starter.

I understand that during starting we're pulling 100s of amps through that wire and that any fuse would need to be very large. So large that maybe it wouldn't really even be providing much protection to that wire for continuous duty amperages.

If something shorted during starting, I'd at least be on the ground. But let's just say that #2 wire chafed through somewhere and grounded to the airframe in flight. What would be my protection?

Just want to make sure I'm most missing something here.
 
I think you hit it in your initial comments- Any kind of fuse there would have to be 200-ish amps. if you got chaffed insulation and shorted to ground somewhere it would melt just about everything in sight before reaching the fuse limit.
 
I thought about this and simply took extra inspection and consideration when running the always-hot wires. Sturdy straps for connection, adel for routing and allowing nothing that can rub. On the 7 there is a relatively short #2, but a few smaller hot wires for sensors that I have limited to a closely mounted fuse block.

I had to repair a Volvo wiring harness where an alternator indicator wire got grounded and merged with its brethren in the harness. A smoking mess. So . . . nothing hot on my plane (except the #2) is routed unfused, especially small wires.
 
Starter cable

The starter cable is only hot when the starter is engaged. Unlikely it will cause a problem in flight unless you have an engine problem. That said, mine is 2AWG welding wire. Very thick insulation and it's also fire sleeved.
The Master feeds the Starter Contactor by a copper bus. Another bus feeds the ANLs then yet another bus to the Shunt. All the busses have multiple wraps of heat shrink where exposed.
 
Well, maybe

wirejock said:
The starter cable is only hot when the starter is engaged. Unlikely it will cause a problem in flight unless you have an engine problem. That said, mine is 2AWG welding wire. Very thick insulation and it's also fire sleeved.
The Master feeds the Starter Contactor by a copper bus. Another bus feeds the ANLs then yet another bus to the Shunt. All the busses have multiple wraps of heat shrink where exposed.
Click to expand...

There are some setups that use that two gauge wire as a B lead from the alternator; in this case, the only wire that is not hot is grime the start contactor to the starter. In most -10s this is a fairly short wire. The rest of the #2 wire remains hot with the alternator/battery on.
 
rocketman1988 said:
There are some setups that use that two gauge wire as a B lead from the alternator; in this case, the only wire that is not hot is grime the start contactor to the starter. In most -10s this is a fairly short wire. The rest of the #2 wire remains hot with the alternator/battery on.
Click to expand...

Yes, mine is a -10 if that wasn't clear. I was worried about the hot #2 running all the way from the battery in the back to the starter solenoid, not necessarily the wire from the solenoid to the starter.

After reading some of the other replies, I'm satisfied that this installation meets the standard of care without additional circuit protection.

Thanks for all the responses!
 
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