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Old 18-01-2017, 13:22   #1
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Fuse/Breaker in battery to started cables?

While installing a new beta 50 in the old 41 Morgan OI I'm wondering what the current thinking is on fusing the battery to starter cables. From a quick googling most would say don't fuse. However, there are some convincing arguments on smaller motors such as a beta 50. Any thoughts?
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Old 18-01-2017, 13:36   #2
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Re: Fuse/Breaker in battery to started cables?

The ABYC doesn't require overcurrent protection in engine starting circuits because the current drawn by the starter would approach the practical value of that protection. You don't want nuisance fuse blowing, especially if you are drifting towards the rocks.




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Old 18-01-2017, 13:39   #3
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Re: Fuse/Breaker in battery to started cables?

Reading previous discussions on the forum if I recall correctly, ABYC doesn't "require" fuses on the cable from the starting battery to the starter but with the battery terminal fuse available at low cost and easy install there's absolutely no reason not to add a bit of safety and fuse that cable. I did it on my boat.

You will hear arguments from some that claim the fuse will blow, you can't start the engine, what if there's an emergency, etc., etc., etc. My answer, these fuses almost never blow if properly sized, if it did blow I can change mine out in a couple of minutes OR I can switch to the house battery immediately as a backup starting source.

Bottom line, I think it's cheap insurance, almost zero potential down side and might save the starter if the solenoid locks up and you don't notice.
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Old 18-01-2017, 13:47   #4
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Re: Fuse/Breaker in battery to started cables?

mainesail has a great writeup on why all battery banks should be fused .
Battery Bank Fusing Photo Gallery by Compass Marine How To at pbase.com
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Old 18-01-2017, 13:50   #5
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Re: Fuse/Breaker in battery to started cables?

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Originally Posted by rwidman View Post
in engine starting circuits because the current drawn by the starter would approach the practical value of that protection.
This might be the case with a large engine in a power boat but a 50 HP sailboat diesel starters typically 125-175 amps. Blueseas terminal fuses come in ratings up to 300 amps.

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You don't want nuisance fuse blowing, especially if you are drifting towards the rocks.
My experience, random nuisance fuse (or circuit breaker) blows are extremely rare. I've had fused systems on boats, cars, houses (a long time ago) electronics, etc that went for years and years with never a blown fuse unless there was a short or large overload. Of course if there is something shorted in a fused system you can go through a large handful of fuses trying to track down and repair the problem.
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Old 18-01-2017, 14:28   #6
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Re: Fuse/Breaker in battery to started cables?

Picking a value between nuisance tripping and the point where the fuse does nothing is the trick. Remember, the resistance of the wiring and the internal resistance of the battery limit the maximum current and the battery power will be quickly depleted.


I figure the ABYC knows what they are talking about. Still, they don't prohibit it so do what you think is best for your situation.
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Old 18-01-2017, 14:42   #7
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Re: Fuse/Breaker in battery to started cables?

As Maine Sail states, the ABYC requirement is more for a pair of giant detroit diesels, not a dinky sailboat engine.

I'd say fuse it.
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Old 18-01-2017, 15:03   #8
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Re: Fuse/Breaker in battery to started cables?

When you think about the starter from a system perspective there are a lot of parts that might fail and leave you in a bind (including a typical 30A in the starter solenoid circuit). ANL type fuses are pretty slow to blow on moderate overload, but will clear a ground fault PDQ. Probably the biggest serious hazard is the insulation chafing through and this will normally produce a fault condition. If something else goes south (or north for those down below) then probably time to open the battery switch. Double insulate the starter cable in the engine compartment (dirt cheap and easy) and then fuse the cable as close to the battery as practical.
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Old 18-01-2017, 16:17   #9
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Re: Fuse/Breaker in battery to started cables?

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Remember, the resistance of the wiring and the internal resistance of the battery limit the maximum current and the battery power will be quickly depleted.
And possibly burn down your boat. A battery is capable of enormous current into a shorted cable.
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Old 18-01-2017, 17:02   #10
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Re: Fuse/Breaker in battery to started cables?

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And possibly burn down your boat. A battery is capable of enormous current into a shorted cable.
Exactly!
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Old 19-01-2017, 08:04   #11
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Re: Fuse/Breaker in battery to started cables?

If one was going to fuse any curcuit. Consider a fast blow fuse between the alternator and the battery bank. It will protect the diodes in a power surge or a loose ground. It needs to be T class fuse.

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Old 19-01-2017, 08:28   #12
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Re: Fuse/Breaker in battery to started cables?

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Originally Posted by michaelmrc View Post
mainesail has a great writeup on why all battery banks should be fused .
Battery Bank Fusing Photo Gallery by Compass Marine How To at pbase.com
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Old 19-01-2017, 08:36   #13
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Re: Fuse/Breaker in battery to started cables?

I put a fuse on my start battery this year. It is WAY higher rated than what the starter would even need and if it blows it means that cable is shorted. In which case my boat wouldn't start whether the fuse blows or not, but with the fuse the boat doesn't burn down!!!!
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Old 19-01-2017, 08:52   #14
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Re: Fuse/Breaker in battery to started cables?

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Picking a value between nuisance tripping and the point where the fuse does nothing is the trick. Remember, the resistance of the wiring and the internal resistance of the battery limit the maximum current and the battery power will be quickly depleted.
This is very bad advice.
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Old 19-01-2017, 09:00   #15
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Re: Fuse/Breaker in battery to started cables?

Having had an earthing fault my starter was using the neg feed to the alternator. The wire was hot, melted and smoking although I didnt fit a fuse but I can see the value but it was such a rare fault I dont think I'll bother. I'm on board when the only high draw non fused event occurs. Fuses also suffer from "necking" with age so a nice 100amop fuse can drop to 20A but still look good.
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