ANL-60 vs 60AMP CB

I know its an electrical forum thread, and I already posted there, but I am still scratching my head, not sure I figured it out yet, so decided to ask you guys in our RV10 group.

I see many install 60AMP CB from alternator to main bus, while installing ANL 60 fuse from main battery to main bus.

If CB is good enough for alternator , why not install the same from main bat to main bus?
I understand the ANL trips slower, and is more tolerant. why would I need tolerance , and if so, why not same with the alternator?

Thanks
Oren

Builder’s choice, but the choice is between a 60amp ANL or a 70amp circuit breaker.

A 60amp circuit breaker will yield nuisance trips as a standard 60amp alternator can, and will exceed 60 amps from time to time depending on how much your battery is depleted after engine start.

Carl

Main bus can draw 200+ amps from the battery while the starter is engaged. 60 amp fuse at the battery is a bad idea unless you have a separate, unfused wire going directly to the starter.

Larry

Carl Froehlich said:

Builder’s choice, but the choice is between a 60amp ANL or a 70amp circuit breaker.

A 60amp circuit breaker will yield nuisance trips as a standard 60amp alternator can, and will exceed 60 amps from time to time depending on how much your battery is depleted after engine start.

Carl

Click to expand...

Carl
you are correct
I did install 70A CB from alternator to Main bus

I am referring to the fuse from main bat to main bus

Please see relevant section,
Its actually a cut from someone else's elec diagarm, which I copied (Thanks D ),
Its the ANL between BAT 3 and BAT 4

BAT2 is directly from battery and BAT5 is main bus

https://photos.app.goo.gl/YttjZqM4ENvzL3oU7

replacing with a 70A CB should give me the option to reset if was flipped during flight, and I see reason why it would flip during regular operation

Oren,

The ANL 60 is located close to the connection to the battery cable on the start relay, and is intended to protect the #6 AWG cable between the main bus and the battery connection, including the current shunt. While you could connect this without the ANL or with a circuit breaker at the main bus, you would be leaving the #6 cable unprotected. In the event of a short to ground on that cable (it is about 4 ft. long and runs through the fire wall, and so could be subject to insulation damage), you would draw the full current available from the battery, which can be in excess of 200 amps. The resulting damage would be extensive.

While it would be nice to protect the #2 AWG cable from the battery to the start relay and then to the starter, that would require a very large fuse due to the high current draw from the starter. And that fuse/circuit breaker would need to be located in the tail cone by the battery. I've never seen an installation like that, but can't say it isn't possible.

The 70 amp circuit breaker on the alternator output is there to protect the alternator output cable the shunt on that cable.

Regards,

Thanks Dave
my intention was not to leave this #6AWG wire un protected, but to replace the ANL with a 70A CB, similar to the alternator.
Wouldn't it give same protection but with an option of an in-flight reset in case was flipped?

Dave, Now after re-reading your answer I finally understnad what you mean.
its not about cutting the line in case of a shortage, but where to cut it, where most dangerous current runs, and thats as close as possible to battery.
If its near the battery (on FW) , a CB is un-reachable anyway, so whats the point?!

Thanks a lot!
Oren

Here is what I think about big 60 & 70 amp fuses(cb's).....

Track the cable placement. What can happen during that run if properly mounted? If a short happens with a 60 amp fuse in line, the material (if it is thin) shorted against will burn away and end the short before the fuse or breaker ever reaches it's limits.

The 6 AWG would need to be pinched against a substantial grounded surface to trip a 60 amp breaker..... If it grounded to the ss firewall at a pass through, it would blow the ss away and the short would end.

The Piper PA 28 151 had it's battery under the back seat. The aluminum cable that powered the entire aircraft went unprotected from the battery solenoid across the spar,along the left side of the fuselage to the firewall where it met the starter sol. and to the main bus.

It's the load on the wire that you are trying to protect. Small wires need protection because they don't carry enough amperage to burn away a surface that they come in contact with....... Big wires 6 AWG have that capability.
Proven with a simple bench test.

Another consideration

Give some thought to the idea of resetting a 60 amp C/B airborne. That is a huge amount of current which would not normally be present in the air. If I were to have that C/B blow I would reduce the electrical load to essential power and land. Troubleshooting is much safer on the ground. If there were a short which the C/B properly protected, you are re-powering the the faulty line. If the C/B itself were to now fail as well, you have an airborne electrical fire.