AWG for Alt to master relay and main buss?

[alpinelakespilot2000]

Van's FWF wiring diagrams for the 60A alternator show 8AWG wire being used between the alternator and the main buss (via a 60A C/B on the panel). Aeroelectric Bob shows 6AWG for the same purpose (but with a 60A current limiter on the firewall in place of the panel mounted C/B).

That run--from alternator, to master relay, to main buss--is only about 5-6 feet total (maybe 10' total if you follow Van's route), and AC43.13b Figure 11-2 shows 8AWG can handle runs of 60A up to 12 feet. Thus, I'm planning to use 8AWG wire from alternator to a 60A current limiter to the master relay (starter relay side), then finally to my main (master) fuse block buss. Any problem with doing this all with 8AWG? If not, why is Bob Nuckoll's showing 6AWG?

Where's George when you need him? Sure hope he's out of purgatory! : )

Thanks.

[tonyjohnson]

Steve,

George posted a good article on this subject, including diagrams on a couple of ways to wire from the alt to the buss or battery. I think he mentions the wire size.

http://www.vansairforce.com/communit...ernator+wiring


Yep, I hope George comes back soon.

[az_gila]

Steve.... #6 or #8 should be fine. I think Bob's earlier Z11 schematics showed a #8 there (that's what I bought), but that may have been for a 40A alternator.

As long as the wire doesn't fry itself (and the AC 43.13 reference says it's OK) a small extra voltage drop caused by a #8 is OK.

The reason is that the Voltage Regulator looks at the voltage at the buss (if you follow Bob's schematics) so it will control the alternator output to keep the bus voltage correct, and that's what we want...

I say leave it at #8...

gil A

[alpinelakespilot2000]

Thanks guys. George's post did help a little.

Thinking aloud here... it just occured to me that a current limiter might require a larger wire than a similarly rated fuse, hence the discrepency I noted above. As I seem to recall (but I'm not at all sure of what follows), while a 60A c/b will blow at anything higher than 60A, a current limiter will allow a temporary surge. (??? I think I got that latter part from B&C's website.) Thus, if I wired with a c/b following Van's, 8AWG would be correct, but if I choose to go with the current limiter instead of the c/b, the wire has be more capable of carrying whatever temporary surge the limiter allows?

Make any sense?

[az_gila]

Originally Posted by alpinelakespilot2000

Thanks guys. George's post did help a little.

Thinking aloud here... it just occured to me that a current limiter might require a larger wire than a similarly rated fuse, hence the discrepency I noted above. As I seem to recall (but I'm not at all sure of what follows), while a 60A c/b will blow at anything higher than 60A, a current limiter will allow a temporary surge. (??? I think I got that latter part from B&C's website.) Thus, if I wired with a c/b following Van's, 8AWG would be correct, but if I choose to go with the current limiter instead of the c/b, the wire has be more capable of carrying whatever temporary surge the limiter allows?

Make any sense?

No... the wire just gets hot when over-rated... and this will happen way before it melts...

The fuse/current limiter will go first... just look at the copper cross-section of the current limiter and the cross-section of the wire.

It's obvious which will melt first...

ADDED

BTW, the 60 Amp breaker won't be a guaranteed "pop" at 61 Amps - here is a typical trip curve for a Klixon aircraft breaker...



gil A

[f1rocket]

I used an 8AWG wire and a 60 AMP current limiter. It has worked fine so far.