Battery fusing

Stu Jackson · Mar 12, 2009

We use the Mega fuses

and don't bother with the covers. They're all in the battery compartment within the 7 foot rule of the battery posts (i. e., PDP for the house bank and + post for the reserve bank). For the fuses, the red plastic battery-cable-cover-type things kept sliding off, even when I cable tied 'em up, so I did away with them. Still keep 'em on the battery posts themselves, though. Ain't nothin' metal flyin' around in our battery box. :dance: Been 10 years now...

Ross · Mar 12, 2009

I don't see a need for more than you discribe. I did have a problem last week with the fuse block in my Volvo wagon. Apparently it developed a resistant contact between the fuse and the fuse holder in a 30 amp circuit and cooked the fuse block. I don't know how to protect against that sort of an event except to remove and replace the fuse once every ten years, Just to clean the contacts.
I have lashed plastic cover shields on the tops of my AGM batteries to prevent anything from falling onto the terminals.

Chuckbear · Mar 12, 2009

Putting a fuse on the starter cable is probably not a good idea, won't help much and you might find yourself unable to start the engine just when you really need to. Lots of good information on OVERCURRENT PROTECTION read ABYC E-11, paragraph 11.12, beginning page 24, at:
http://www.boatdesign.net/boat-desig...ricalGuide.pdf
and also see
Figures 10 (A & B) pages 41, 42, etc

Maine Sail · Mar 12, 2009

Roger Long said:
I am going to add battery fuses to my system. I was looking at the Blue Sea ANL fuses and blocks but that still leaves me with an unprotected short cable attached to each battery and just plastic covers to protect the terminals in the engine compartment. Seems to me like the best place for the fuse is right on the battery terminal, at least with AGM's that don't give off a lot of hydrogen.

The Blue Sea Class T fuses come up to 400 amps which should be enough for a 20 hp engine starter. My terminals are the kind that just have a bolt. Is there any reason not to just bolt one of these fuses to each battery and then bolt the cable to the other end?

These are for last ditch protection in case of major havoc in the engine compartment or a battery cable being compromised. I expect I would be doing a lot more than just replacing a fuse in a situation where one of them blew.

Roger put it on the negative lead then no worries about covers etc. A short can't tell if the fuse is on the positive or neg lead. If you don't have ground you no longer have a short..

I tend to disagree with the ABYC on not fusing starter leads. ABYC is a good standard but they are the minimum safety standard not the maximum.

As long as you know the KW or amp draw of your starter and size the ANL appropriately you will not have an issue. I always start on my house bank and house banks need to be fused to abide by the current CFR builders code on a new vessel. I also have a fuse on my emergency / back up battery. Ten+ years & I've never blown even one ANL during starting. Also my Catalina came from the factory with two ANL fuses one for each bank so some builders go above the standard too not just me.

Ron20324 · Mar 12, 2009

MS, you surprise me. I didn't look a whole lot in the books on the matter, but the fellow who lived next door and worked installing new electronics on new boats told me you DO NOT put fuses in the negative cables. I had a spare circuit breaker and was thinking of putting it on the neg battery feed, but just the one to the DC panel. I was thinking I could move the breaker down in size to just above where keying the mike would blow the breaker. He said, no, No, NO! Reason? With a blown neg fuse, most all of the other cables would still be energized and you still have other battery negs and the shore power ground looking for juice! I don't think you'll find wiring diagrams with ground fuses.

Actually, there IS a fuse that bolts right on the battery post. I have some (not installed because of clearance to the bunk board), and have seen them in a catalog (not West or Defender) recently but don't recall which one. Is a square plastic gizmo you put on the post then put the cable on top and bolt it. Beneteau has it in the parts department.

Bill Roosa · Mar 12, 2009

Fusing and # of connections

Given that we operate in a corrosive environment you really want to fuse where it makes sense. Adding fuses to several + terminals only gets you more opportunities to have then corrode and give you problems. Better to have one fuse on the ground side (flame on!) for the high amp cables to minimize the number of connections that corrosion can effect.
The problem then becomes how can I protect my primary leads to my secondary (panel) circuits and the start and charge cables. There is not much that the panel cable sees in the way of vibration, heat..... that will cause it to fail so just make sure all the places it goes through bulkheads are grometted or protected from chafe. The start and charge circuits just need to be checked regularly and run so that they don't get chafe

Maine Sail · Mar 12, 2009

Only suggesting this for

Ron20324 said:
With a blown neg fuse, most all of the other cables would still be energized and you still have other battery negs and the shore power ground looking for juice! I don't think you'll find wiring diagrams with ground fuses.

I am not suggesting this on equipment leads but on the negative battery lead. If it blows it does not matter how many wires you have looking for juice as you've disconnected your battery. Take your ground lead off your batt and try to fire up your panel or bilge pump.

If you need USCG certification as a charter vessel then you'll need to put it on the positive side. Don't ask why they mandate this? I don't know.. The fuse will blow on either side of the battery and in both cases it disconnects the battery from the vessel which is the entire point of having a fuse close to the battery..

Chuckbear · Mar 12, 2009

Roger Long said:
I've got the whole ABYC book right here on my shelf but I take it with a grain of salt on my own boat. I have the classic 70's vintage set up where the starter lead goes to the battery switch. My engine starts so easily that I haven't felt the need to change it or have a dedicated starting battery. I just switch to "Both" when I get on the boat and "Off" when I leave it. This means the starter would have to pull 800 amps to blow the fuses, not very likely unless there is a problem severe enough that I probably shouldn't be trying to start the engine anyway.

Roger, Blowing the fuse is not the only way to keep the engine from starting. All it takes is a little corrosion and you can't start the engine. So why add a weak link to an important piece of equipment. In 40 years in the service end of this business I have never encountered a situation where a fuse in the starter cable would have been of any benefit. I would suggest that the starter cable be connected directly to a battery and not a switch. Battery switches do fail. If it is connected to a switch then a fuse between the battery and the switch would be more helpful but not necessary to add another between the switch and the starter. BTW, NEVER use a circuit breaker on the battery cables. Always use the appropriate fuses.

Ron20324 · Mar 12, 2009

Roger, and all: The 2009 West catalog has, on page 279, the fuse I refered to. It can actually be placed on ANY 3/8-size electric post. This means you could put it on a battery, battery selector switch, inverter, whatever. From 30 to 300 amps. 15 bucks.

For others, lacking any printed backup, I would only say if neg battery fuses were a good idea, you'd see them in use somewhere. Or are ALL the boat builders wrong? Say you blow a fuse on one house battery, or maybe you just pop the fuse off to do some work. You still have another battery or two or more looking for some fingers to fry.

Maine Sail · Mar 12, 2009

Fusing..

Ron20324 said:
For others, lacking any printed backup, I would only say if neg battery fuses were a good idea, you'd see them in use somewhere. Or are ALL the boat builders wrong? Say you blow a fuse on one house battery, or maybe you just pop the fuse off to do some work. You still have another battery or two or more looking for some fingers to fry.

I just want to be clear, I have my fuses on the pos side of the battery. If the question becomes, as it seemed to above in the OP, no fuse, or fuse the negative I'd always opt to at least fuse the negative over nothing at all.

As I have said before the builders need to build to the CFR and that dictates pos side so builders comply.

As for "lacking printed back up" Ample Power actually suggests fusing the neg side..

Ample Power said:
Fusing: Why do your drawings show a main battery fuse on the negative lead? I thought you were supposed to fuse on the positive wire.

A great amount of thought has gone into the proper location for a main battery fuse. We wish to achieve safety with a minimum cost, which fusing on the negative side of a battery permits. If someone were to give you a sealed box with a battery and a fuse inside it, you would not be able to determine which side of the battery was fused by any kind of electrical measurement. That being a fact, why not put the fuse where it will be most economical? If you put the fuse on the negative side, it will not need to be insulated. Even if you do drop a wrench on the fuse, shorting it to your metal hull, no electrical damage will result.
A fuse on the positive side must be enclosed inside an insulator of some sort, which adds unnecessary cost to the system. Should you fuse on the positive side? If you need Coast Guard certification, then you will have to put the fuse in the positive lead of the battery

Ample Power is a fairly well respected source..

I would guess that most boats on this forum are wired with a 1/2/BOTH/OFF switch and do not have a direct wired start battery. If either bank 1 or 2 can act as a house bank, via a switch, I still think it is safe and prudent to fuse close to the battery..