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ANL Fuse Proximity to Contactors

rockitdoc

Well Known Member
Sponsor
I have read/seen the location of the ANL fuses between the B leads on alternators (Littlefuse Midi's in my case) placed immediately next to the contactors. In fact, some even connect them via hard copper bars.

In my case with the -14A this puts the fuses under the contactors on the firewall and difficult to access/inspect/replace. Is there a compelling reason why I do not want the fuses on the upper firewall above the contactors? I would connect with the same 6AWG from the main alternator and 10AWG for the backup wires for about a 12 inch run.
 
Nope - not an issue

Here's my thinking - the only way to get enough current to blow the fuse is from the battery - no way the alternator can generate it. We are most likely protecting against a most likely a dead short at the Alternator.

In this scenario the whole length of 6AWG is carrying the load until the ANL blows, regardless of where the fuse is.

If the short is caused by the 6AWG wire chafing to ground the ANL provides protection that would keep the lights on, so keep the length to the fuse short and well supported and you have an equivalent solution.
 
Here's my thinking - the only way to get enough current to blow the fuse is from the battery - no way the alternator can generate it. We are most likely protecting against a most likely a dead short at the Alternator.

In this scenario the whole length of 6AWG is carrying the load until the ANL blows, regardless of where the fuse is.

If the short is caused by the 6AWG wire chafing to ground the ANL provides protection that would keep the lights on, so keep the length to the fuse short and well supported and you have an equivalent solution.

When you say short, you mean between fuse and contactor? Is 12” short if its well supported?
 
Yes and yes.

Many aircraft don't even have the ANL at all, so for the length between the contactor and the fuse you are the same as many certified airplanes. If that wire shorts you have to turn off the contactor and everything goes black, if it shorts beyond the fuse, then the fuse blows and you have power until the battery runs down.

12" counts as short, but the length isn't the factor as much as: is there anything that could potentially chafe on it before it gets to the fuse - the advantage of the brass bar is that question is soundly answered which is why folks do it
 
Excellent

Yes and yes.

Many aircraft don't even have the ANL at all, so for the length between the contactor and the fuse you are the same as many certified airplanes. If that wire shorts you have to turn off the contactor and everything goes black, if it shorts beyond the fuse, then the fuse blows and you have power until the battery runs down.

12" counts as short, but the length isn't the factor as much as: is there anything that could potentially chafe on it before it gets to the fuse - the advantage of the brass bar is that question is soundly answered which is why folks do it

Thank you. Onward and up.
 
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