Alternator output wire size question

[jt11791]

Both of my alternators' outputs go through fuses (breakers) on the way to the 1-2-both switch. Protects from alternator shorts and good if I need to remove an alternator.

[mitiempo]

Originally Posted by Buster007

the house bank positive will be fused. i understand no need to fuse the starter battery per ABYC

Actually that is not correct.

ABYC does not require a dedicated start battery to be fused. By dedicated they mean a battery that can not be used for anything except engine starting. Battery to simple on/off switch and to starter.

With a 1/2/both/off switch either battery can be used for any load so both batteries do need fusing.

It is not hard to do. I fuse start circuits regularly, most often with a fuse of about 250 amps. Typically wired with 2/0.

[mitiempo]

Originally Posted by Celestialsailor

I have never seen a fuse on an alternator. If a short developed "in" an alternator the diodes would blow. Yes, It's quite common to fuse at the common on the battery switch.

An alternator is a current limited device. As long as the wire is sized properly a fuse is not needed at the alternator.

The battery is the source that can cause the problem. That is why fusing should always be at the battery end of a cable, not at the load end.

smac999 is correct, only fuse if the wire is led from the alt to a battery directly.

[Celestialsailor]

Originally Posted by mitiempo

An alternator is a current limited device. As long as the wire is sized properly a fuse is not needed at the alternator.

The battery is the source that can cause the problem. That is why fusing should always be at the battery end of a cable, not at the load end.

smac999 is correct, only fuse if the wire is led from the alt to a battery directly.

I think we were on the same page. I usually fuse the common on the 1/2/ALL/OFF selector switch and yes, in most cases 2/0 is most sufficient for a cable run (depending on distance run of course). Still, fusing the alternator is not a practice that I have seen. More importantly IMHO is proper routing and chafe protection of the large battery cables. Over time with a multitude of wire changes and add-ons, the cables can get covered by a birds nest of wire and if there is a chafe problem, hard to see before it is too late.