SailNet Community banner
1 - 12 of 12 Posts

bell ringer
Joined
5,258 Posts
Discussion Starter · #1 ·
I am sure my boat was wired per the ABYC codes of 2000 when it was built. But the last couple of days chasing an issue has me shocked at how much isn't protected from a high current grounding.

My house batteries have 4/0 cable and a 300A fuse. But feeds a cable via a switch to the inverter that is smaller without protection as the 300A one is too big. The start battery of course didn't come with any protection. I since added a fuse at the start battery, But that doesn't protect all the cabling etc. if I run the starter off the house battery. The alternator cabling has no protection at all.

Now I know some argue that "you don't what a blown fuse to stop you starting the engine". My position what good is that when your boat is on fire.

I bet I can add fuses to all these things for less than $200.
 

bell ringer
Joined
5,258 Posts
Discussion Starter · #2 ·
I bet I can add fuses to all these things for less than $200.
WOW was I ever wrong!

I can do this for around $20 with some MIDI fuses.
 

bell ringer
Joined
5,258 Posts
Discussion Starter · #3 ·
Turns out that big 300A house battery fuse on the 4/0 cable is actually still protection for the 2/0 cable that feeds into my start circuit from the house. So all I need is an alternator fuse as I already have 1 on the start battery. So it is now $10 or just be too lazy to do it.
 

bell ringer
Joined
5,258 Posts
Discussion Starter · #4 ·
I added that alternator fuse. The added benefit was i discovereed a mystery that had me going crazy and wasnt related.

But the crazy thing about this thread is it appears no one was concerned enough to look into their cable protection.
 

Registered
2003 Hunter 356
Joined
65 Posts
I added that alternator fuse. The added benefit was i discovereed a mystery that had me going crazy and wasnt related.

But the crazy thing about this thread is it appears no one was concerned enough to look into their cable protection.
Do you have your alternator wired in to a bus bar direct to the batteries?

Have the original stock alternator and was thinking of upgrading to higher amp external regulated alternator and wire direct to house bank, with fusing it seems :)

Jeff
 

bell ringer
Joined
5,258 Posts
Discussion Starter · #6 ·
no bus bar, my alternator connects to an isolator and feeds to the house and starter batteries from there
 

Registered
Aloha 32 & Hunter 26.5
Joined
236 Posts
Most of the time, an alternator is wired straight to the battery. The alternator is a special case that normally is not fused because if that fuse blows, it will usually take out the regulator & stop the alternator from working, even after the fuse is replaced.
 

bell ringer
Joined
5,258 Posts
Discussion Starter · #8 · (Edited)
As opposed to shorting out, blowing apart, and causing a fire.

I will chose to have to replace the alternator instead of the boat.

It is the same twisted logic used to not fuse the start battery, because if it blows you can not start the engine. Sorry but if the cable shorted enough to blow the fuse you were never starting that engine! In my opinion of course.
 

Registered
Aloha 32 & Hunter 26.5
Joined
236 Posts
As opposed to shorting out, blowing apart, and causing a fire.

I will chose to have to replace the alternator instead off the boat.

It is the same twisted logic used to not fuse the start battery, because if it blows you can not start the engine. Sorry but if the cable shorted enough to blow the fuse you were never starting that engine! In my opinion of course.
There are times when common wisdom is not the wisest path to follow.

Although I have seen it in print from manufacturers that the heavy alternator wire should be connected directly to the battery, I share your concerns & I appreciate the reasons for your decision. What we have here is a risk/benefit assessment. Not everyone will reach the same conclusion. A similar debate sometimes occurs when people suggest wiring a bilge pump directly to a battery, bypassing the AB switch.
 

Registered
Joined
4,735 Posts
Wiring through an isolator is essentially wiring straight to the battery in an electrical sense. Both batteries, in fact. It is similar in concept to an external diode pack - which isn't considered "not straight to the battery" just because it physically exists between the wire run from the alternator body to the battery.

It is definitely a different electrical argument than wiring a bilge pump directly to the battery (the debate of which I've never heard).

Mark
 

Super Moderator
Joined
6,815 Posts
Most of the time, an alternator is wired straight to the battery. The alternator is a special case that normally is not fused because if that fuse blows, it will usually take out the regulator & stop the alternator from working, even after the fuse is replaced.
The alternator end of the wire, provided it is sized correctly, is not fused because under ABYC standards the alternator is classed as a "current limited" device. The wire needs no over-current protection from the alternator because the alternator does not have enough current, even in a failure mode, to damage the wire. In other words your 100A alterntor cannot fail and drive upwards of 3000A - 10,000A+ into a dead short, but the battery end can. A single G-31 TPPL AGM can deliver as much as 5000A into a dead short. Sadly we see far too many fuses for alternators installed at the wrong end of the wire. The fuse always goes at the battery bank end of the alternator B+/Output wire.

The alternator B+/Output wire does need a fuse at the battery end of the wire. Any fuse for an alternator needs to be sized at a minimum of 140% to 150% of the alternators rated output. Boat builders get around this by taking the cheap way out and wiring the alternator directly to the starter post and the cranking conductor does not require over-current protection.
 

bell ringer
Joined
5,258 Posts
Discussion Starter · #12 · (Edited)
The alternator B+/Output wire does need a fuse at the battery end of the wire
Can/does the main fuse at the house battery be considered the fuse for this? - never mind I found the ABYC fuse/cable chart so the answer is NO unless the alternator cable is as big as the battery cable

I don't feel my alternator before I installed a fuse meets the below. I don't know what is considered "integral regulators", but the alternator is definitely more than 40"
4. Overcurrent protection is not required in conductors from self-limiting alternators with integral regulators if the conductor is less than 40 inches (1.02m), is connected to a source of power other than the battery, and is contained throughout its entire distance in a sheath or enclosure.

I am more interested in having protection make sense and able to do it's function over "just meeting" a requirement. I have no problem installing fuses on both ends of my alternator cable and hadn't really thought power going from the battery to the alternator.
 
1 - 12 of 12 Posts
Top