Breaker vs. ANL fuse for Alt on Firewall

I have the Van's 60A alternator and want to protect the "big" wire before it goes into the main buss on the firewall side. I see some choose the 60A ANL fuse and some seem to pick a 60A CB. Are there benefits to one or the other? I wonder about heat and moisture with a CB but the ability to reset the breaker while away from home might be good too. Thoughts?
THANKS!
Mark

MarkChristopher said:

I have the Van's 60A alternator and want to protect the "big" wire before it goes into the main buss on the firewall side. I see some choose the 60A ANL fuse and some seem to pick a 60A CB. Are there benefits to one or the other? I wonder about heat and moisture with a CB but the ability to reset the breaker while away from home might be good too. Thoughts?
THANKS!
Mark

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Hi Mark. Just to be clear, the purpose of the breaker or ANL is to protect the alternator + wire from an alternator short. If your battery and contactor are on the firewall, then the ANL is the most convenient method.

If your battery is elsewhere, you have the option of the breaker if you want. Typically, the breaker is mounted on the breaker panel along with all of the main load breakers, although I've even seen a 60A breaker mounted to the firewall instead of an ANL.

Don't overthink it... just remember you are protecting the wire from an alternator short.

I think he's asking, will a circuit breaker work mounted somewhere forward of the firewall...?

Thanks guys. Since the battery is the what I want to keep from being grounded in the case of a shorted Alt wire, I want to protect the circuit right at the switched side of the battery contactor. Therefore, can I mount a CB forward of the firewall in the engine compartment? The only advantage I can see is possibly being able to ground reset it if it were to trip which seems like a good idea. I just don't know about its longevity in that environment.

Breaker vs ANL

Another consideration is protecting that big wire from the alternator to the overcurrent protection device. If you mount a CB on the panel, to facilitate a reset for example, then you have a long run of unprotected 10 gauge wire. I use an ANL fuse right next to the alternator. Resetting a 60 amp tripped CB in flight is not a good idea.

I don't think the engine compartment near the alternator is an acceptable environment for a CB for long term reliability.

When it comes to fat wires in our airplanes, the primary source of current large enough to smoke the fat wires is the battery. The protection should be as close to the battery as possible.

Most people install the protective device in the alternator B Lead as close to the battery as they can. Some of us take it an extra step and also install a protective device on the main bus feed as close to the battery as possible.

ANL's are simple, cost effective and proven for their intended purpose. Never heard of one blowing for no reason if it was installed and sized correctly.

A breaker on the engine side of the firewall may work just as good if it is properly spec'd. Some are thermal devices and their trip characteristics can be significantly altered by the ambient temp. Take a look at the published trip curves for any device you are considering.