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Battery Fuse Block

EGregerson

Member III
I'm trying to decide what amp fuse to install on a battery block: i.e. the Blue Seas Block Terminal. I contacted Blue Seas, stating that i have 2 group 29 batteries with a reserve of 170 amps; plus a starting battery. They replied it's not a matter of battery amps, but what size wire I'm trying to protect. Ok. How about 1/0; I got no reply. It seems I would need something less than a 170 amp fuse for the house bank. Is there a rule of thumb estimate? O Simply add up the value of the breakers on the electrical panel? Then there's the question of cranking amps. If the starting battery has 600 cranking amps, hows does that enter the equation? And the glow plugs? I'd like to hear your thots and experience with this.
 

toddster

Curator of Broken Parts
Blogs Author
Sounds like you need a copy of "Boat Owners Mechanical and Electrical Manual, by Nigel Calder."

The battery specs really have nothing to do with your fusing. Assume that they are far in excess of the loads that the wires will carry.
1/0 wire is rated for something like 280 amps. Any fuse that blows at or below that will protect those wires. Every time you step down in wire size (or add a device) you need another fuse or breaker to protect that smaller wire.

The number you need is how many amps it takes to start your particular engine, then add a generous buffer that is still within the ampacity of your wire.

For example, I believe I have a 120 amp fuse on the battery terminals, to protect the wires running from the battery to the A/B switch, and the engine, all of which are capable of handling 160 amps. (My engine needs only about 60 or 70 amps to start.) Between the main switch and the hot bus behind the house panel, there is a 30 amp main breaker. The hot bus feeds all the branch circuits, each of which has its own appropriately-sized breaker. Within the engine bay, each wire that is rated at less than 150 amps has its own fuse or breaker.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
And, while the subject is "current', as it were,
Any opinion on using large expensive fuses vs a circuit breaker that could be reset?

Loren
 

toddster

Curator of Broken Parts
Blogs Author
And, while the subject is "current', as it were,
Any opinion on using large expensive fuses vs a circuit breaker that could be reset?

Loren

I prefer using breakers, for the obvious reason that stocking and finding the appropriate spare fuse in the middle of nowhere is much more difficult than resetting a breaker.
Some people prefer fuses because they are simple, cheaper than breakers, and it's easy to see if they're blown. Breakers do sometimes go bad, and it's usually a head-scratcher when they do. Plus then you need a spare breaker. (I usually assume that I can "borrow" a breaker from a less important circuit, assuming there is more than one of that size.)

But the Blue Sea terminal blocks are the only product I know of that protects the entire battery cable. It seems like we hear about a lot of boats lost to fires caused by shorted battery cables. That doesn't mean there isn't something I don't know about. I have a truck winch that came with some sort of thermal breaker that goes between the terminal and the cable, but it's a nightmare of exposed (Chinese) energized metal, and doesn't fit well. I tossed it and put in a Blue Seas ANL fuse block.
 
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Shelman

Member III
Blogs Author
Looks loke 175 amp fuse if inside engine bay for 0awg.
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I have the blue sea terminal fuses on the battery which are ignition protected terminal fuses. and breakers in the electrical pannel. Nuisance shorts and bumps are taken care of by the breaker pannel and only a short between the panel and the battery would have to be absorbed by the main fuse.
 

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markvone

Sustaining Member
MaineSail How-To article to the rescue

I just did this last winter. I followed the MaineSail How-to. I have 2/0 cables so I used 300A Blue Seas fuses. I had one smaller cable for something else that I used the Blue Seas double terminal with a 100A and a 300A on it. No problems so far. Note, you need approx. 2 inches of vertical clearance above your batteries for the new fuse terminal - check the Blue Seas website for the exact number.

I still have a half dozen small wires that are fused further than 7 inches from the battery terminal, due to my battery arrangement, but they are fused. My boat's PO was a Caltech electrical engineer! :egrin: Blue Seas makes another terminal attached block that takes the small amperage blade fuses, like cars use, that works well for the small size wires.

Mark

http://www.pbase.com/mainecruising/battery_fusing
 

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Shelman

Member III
Blogs Author
You can also reduce the clearence needed by just a bit if its tight by trimming the extra 3/8" off the top of the stud on the fuse holder. Mine just barely fits under the lid after a bit of a trim and a slight bending of the base plate.
 

EGregerson

Member III
Fuse

Thanks all for the input. I got wrapped around the axle but it looks good now. No needs to determine total load demand downstream; or wonder what the 'current ' amp capacity of my 5 year old battery is. Just size the fuse to the wire: e.g. 250 amp fuse for a 1/0 cable. Fair winds!
 
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