Electrical question

[porman]

In preparation for replacing my old diode style battery isolator with a new Blue Seas ACR I made a diagram of my batteries and chargers. I noticed that the big 2/0 battery cables run directly from the batteries to the battery switches without any over-current protection. Calder says any run over 6 feet should have protection. My question is how many of you have protection on those cables? I've been on a lot of boats and never seen any.

 

[tiltrider1]

I think most of those boats had fuses that you just didn’t recognize I would be surprised if anyone here has an unprotected run.

 

[SteveK]

Start batteries are not required to have Fuse or overcurrent protection, you have not said what batteries are on the isolator and will be on the ACR.

 

[fgarriso]

My boat has 2/0 cables that run from the battery bank to the starters without any breakers or fuses on them.

 

[Comodave]

Here is the ABYC recommendations.

Mounting placement dimensions for a fuse or circuit breaker (7"/40"/72" ABYC rule): 7 inch maximum if the conductor is not housed in a sheath or enclosure
in addition to the wire insulation, 40 inch maximum if the conductor is housed in a sheath or enclosure in addition to the wire insulation, 72 inch maximum
if the conductor is connected directly to the battery and housed in a sheath or enclosure in addition to the wire insulation.

 

[Flatswing]

Both Steve K & Comodave are correct. Can you provide more information about which batteries you are isolating? The fusing requirements (type and size) for your house bank will depend on the banks storage capacity. If you choose to fuse your start bank cables, best to know the actual current draw for your diesel’s starter during prolonged cranking.

 

[porman]

In typical Mainship fashion the two start batteries also supply power to the electrical panel. No house bank as original equipment. This boat has an additional 3 batteries that supply power to a 3000 watt inverter/charger, and also to the bow thruster. The thruster circuit and inverter circuit are protected. This bank is not connected to any 12 volt house circuits. The diode isolator lets one alternator charge one start battery and the 3 additional batteries. All batteries are 8D deep cycle. The cable runs from the start batteries to the battery switches, not the starters, are longer than 6 feet. After more than 40 years as a car mechanic I hope that I could recognize any type of current protection in a battery cable, and I don't see any.

 

[Flatswing]

It sounds like you have start batteries connected to battery switches then individual cables to starters and house loads. A common set up allowing easy disconnect to safely work on starters etc. Perhaps wise to fuse the run from switch to house bus.
To answer your original question: Given that most boat fires are electrical in origin, I elected to upsize many cables & fuse all power sources (including start batteries to starters.) This was not an inexpensive change since I have a 1200Ah house/inverter bank and my starters pull just over 500A continuous from their respective Grouo 31’s, so big a** Type T fuses and holders in addition to a host of MRBF fuses appropriate to each cable.

 

[porman]

The main electrical distribution breaker panel is right next to the two battery switches so the runs are very short. Not too worried about them. I will look into the type T fuses and see it I can work them into the system. DeFever 49, one of my favorite boats. I got to drive one from the Anacortes Trawlerfest back to Seattle a few years ago.

 

[Bob Cofer]

These are a great option for retrofitting an established system.

5191 Blue Sea Systems 5191 Fuse Block for Terminal Fuse

Blue Sea Systems 5191 Fuse Block for Single Battery Terminal Fuse

www.boatwireusa.com

 

[Comodave]

These are a great option for retrofitting an established system.

5191 Blue Sea Systems 5191 Fuse Block for Terminal Fuse

Blue Sea Systems 5191 Fuse Block for Single Battery Terminal Fuse

www.boatwireusa.com

I use these quite often. But they only go up to 300 amps and that will not start my 8.3L diesels. They did work on a previous boat that had 318 gas engines.

 

[SteveK]

I have wondered if a dead short of a 12-14G wire would blow a 400A fuse or if the wire would explode first. Most likely the average 15A fuse/breaker would trip first.
Now a house bank battery to an inverter can suck up enough power to blow that fuse. Same as a starter needing high amp short duration draw.
Maybe the reason a lot of boats from the factory before big house banks did not have any fusing before the distribution fuse box.

 

[Comodave]

Why would you have a 400 amp fuse on 12 or 14 gauge wire in the first place? They are rated for 15 to 20 amps.

 

[CharlieJ]

ABYC Electrical Standard requires every B+, with the exception of the starting battery cable, to be protected.

 

[SteveK]

Why would you have a 400 amp fuse on 12 or 14 gauge wire in the first place? They are rated for 15 to 20 amps.

Well Dave, I am following the posts made by the OP who is talking about installing an overcurrent protection on 2/0 wire but 300A is not enough as the starter draws more. So I used a 400A for my question since the bat cable to the DC fuse box may also be 2/0.
Maybe I was being hypothetically devilish.
But never mind that, what do you think would blow first, 12-14g wire or 400A fuse on a dead short?

 

[High Wire]

But never mind that, what do you think would blow first, 12-14g wire or 400A fuse on a dead short?

My money would be on the wire going first. 400A through a 14 or even 12 gauge wire would have it glowing like a lightbulb. Its amazing that much current can flow thru a fuse with a tiny diameter conductor and survive. FWIW, back when we were stupid kids we played with old boat batteries and a hacksaw blade. Yes they not only glowed but melted the terminals down too until the blade melted in half.