Help! Burnt wire!

[zenoahphobic]

So we accept the fix is to cleanup all ground connections there are no other faults; this fixes the problem. The way a mechanic would think, he just needs to fix the problem and doesn't necessarily need to know all the how's and why's.

Going back to that OPs specific wire, we then must assume that wire was attached to some high current component carrying its earth because it's normal earth became loose or dirty. It then travelled down that wire to some lump of metal that already had good connection back up to the engine block that in turn had good connection back to the battery.
So this becomes a design issue in that that wire shared a ground connection with a heavy ground connection, it should have had its own connection point!

[TownsendsFJR1300]

So we accept the fix is to cleanup all ground connections there are no other faults; this fixes the problem. The way a mechanic would think, he just needs to fix the problem and doesn't necessarily need to know all the how's and why's.

Going back to that OPs specific wire, we then must assume that wire was attached to some high current component carrying its earth because it's normal earth became loose or dirty. It then travelled down that wire to some lump of metal that already had good connection back up to the engine block that in turn had good connection back to the battery.
So this becomes a design issue in that that wire shared a ground connection with a heavy ground connection, it should have had its own connection point!

T&T unit? ……….

[boscoe99]

I can see, and read, that - but I'm not 'getting' it.

I too know that it happens. I also am not "getting" the way behind it.

Unfortunately, the theory of what goes on is often left far behind. Wish that it were not so but...

[99yam40]

So clearly with Evinrudes explanation, this burning of small gauge wires may happen when there is ANOTHER fault condition, not from loose earths alone!

read it again, it was not talking about bonding wires metling in that portion, it was talking about accessory wiring can melt from a short among other thing mentioned

[99yam40]

I too know that it happens. I also am not "getting" the way behind it.

Unfortunately, the theory of what goes on is often left far behind. Wish that it were not so but...

As I said before most boats that have multiple batteries have all of the negatives commoned(tied together).
if one has a bad connection it will seek out the least resistance to get back to the original battery.
It will not and cannot flow to a different battery. it has to get back to the original that the electrons came from.
metal hull boats I can understand it flowing thru the hull, but not fiberglass hulls,
so there has to be another ground wire that has less resistance than the main one with a bad connection

[99yam40]

T&T unit? ……….

T&T,starter, and the charging system are all possibilities

[zenoahphobic]

read it again, it was not talking about bonding wires metling in that portion, it was talking about accessory wiring can melt from a short among other thing mentioned

You are right.

I guess the struggle I have with this is for the bonding wire to melt there must actually be TWO faults.

That is the heavy earth wire has lost good earth connection (1), and the bonding wire has lost good earth connection(2), as this bonding wire would not carry that heavy earth wire current if it maintained good earth. So there is a condition where the bonding wire has maintained a good connection with the heavy earth wire but lost good connection with earth.
And this burning of the bonding wire of course could have been avoided by proper design, the two earths of different current carrying capacity, should never be joined together on the one post or bolt.

[zenoahphobic]

As I said before most boats that have multiple batteries have all of the negatives commoned(tied together).
if one has a bad connection it will seek out the least resistance to get back to the original battery.
It will not and cannot flow to a different battery. it has to get back to the original that the electrons came from.
metal hull boats I can understand it flowing thru the hull, but not fiberglass hulls,
so there has to be another ground wire that has less resistance than the main one with a bad connection

What happens when batteries are connected in parallel, the electrons flow from one to the other. Connected in series they do that as well but go on a longer journey doing so.
Electrons don't care where they go and nor do batteries, they don't need to go back to the battery that they come from. It's just a numbers ****, a battery strongly prefers an electron to be ready to come aboard before releasing one.
What this means relative to the subject, one battery can influence another battery simply by having wires near each other through capacitance, inductance, moist air transfer and other "leakages". This why we have some strange happenings like earth loops etc., mysterious voltage etc etc.

[99yam40]

Normally house and start batteries are not hooked up in series or in parallel with each other,
their negatives are just commoned in all of the set ups I have seen.
if one negative gets a bad connection, the electrons will try to find a different path to eventually get back to the battery