Battery fusing

[brettportzer]

Starting to clean up some wiring issues, and am not sure how to proceed with the following, which is a survey recommendation:

"Install over-current protection in positive battery cables close to batteries in the form of slow blow fuse rated for wire gauge. All other wires should be taking off of buss bar aft of disconnect switch."

I have been doing a lot of reading, etc, but it's mostly people arguing or stuff that is inconclusive.

Basically, I have 2 8d batteries at 12v in parallel for each 6-71 engine. The positive 4/0 wire goes to the battery switch, but also attached to the terminal on the port side are the cables for generator start and on the starboard side the cables going to the main DC panel.

It seems to me that I need to be fusing the 4/0 cable coming from the battery, then going to a terminal block.

What I am confused about is various fusing options and ratings, and what seems like disagreement over whether it is required, what size fuse to use (the Blue Sea MRBF goes to 300a), etc...

What are you guys running on your boats that are at least somewhat similar to mine?

Thanks!!

 

[Jammin']

The starter is not fused. Nothing was fused at the batteries on my boat. I've used terminal fuses at the batteries where I thought it was appropriate. https://shop.pkys.com/Terminal-Fuses_c_71.html Supposedly you are fusing the wire and not the load.

 

[Pascal]

I can’t imagine putting a fuse on the starter wires. Protecting the wiring to the DC panel(s) sure but I wouldn’t use a fuse. I d rather use a breaker like these

https://www.westmarine.com/buy/blue-sea-systems--285-series-thermal-circuit-breaker-30a--P011975596

 

[Jammin']

The photo below is when I was still sorting out the installation of a shunt for a battery monitor, which you can see on the right, and I was still working out the cabling. You can see a double fuse block on the positive terminal. There are two 4/0 cables with no fusing at the battery. One goes to the battery switch. The battery charger wire is attached at the battery switch to the always hot side and I installed a terminal fuse for that wire there. The other 4/0 wire is for the bow thruster. I didn't even try and fuse that, but the thruster switch is nearby. The sanitation system feed is not fused at the battery as it's supposed to be in accordance with ABYC standards, but the fuse block for it is close enough by that there's not much of a cable run for there to be a problem in.

By the way, I'm an amateur. I had to learn this stuff because there's nobody near me - but me! There are far more qualified people on here to give you feedback, but we have the same boats and are going through the same things.

 

[brettportzer]

The photo below is when I was still sorting out the installation of a shunt for a battery monitor, which you can see on the right, and I was still working out the cabling. You can see a double fuse block on the positive terminal. There are two 4/0 cables with no fusing at the battery. One goes to the battery switch. The battery charger wire is attached at the battery switch to the always hot side and I installed a terminal fuse for that wire there. The other 4/0 wire is for the bow thruster. I didn't even try and fuse that, but the thruster switch is nearby. The sanitation system feed is not fused at the battery as it's supposed to be in accordance with ABYC standards, but the fuse block for it is close enough by that there's not much of a cable run for there to be a problem in.

By the way, I'm an amateur. I had to learn this stuff because there's nobody near me - but me! There are far more qualified people on here to give you feedback, but we have the same boats and are going through the same things.

View attachment 46741

Indeed, we are!

Here are a few photos of what I did with my battery box situation, the fiberglass boxes were really beat from getting neglected and I wanted a removeable solution such that things on that side of the engine could be more easily accessed.

Trying to make things serviceable as much as possible.

 

[brettportzer]

The dual 8d box installed.

Actually, these are test fits, I did paint it before I put them in!

 

[brettportzer]

The photo below is when I was still sorting out the installation of a shunt for a battery monitor, which you can see on the right, and I was still working out the cabling. You can see a double fuse block on the positive terminal. There are two 4/0 cables with no fusing at the battery. One goes to the battery switch. The battery charger wire is attached at the battery switch to the always hot side and I installed a terminal fuse for that wire there. The other 4/0 wire is for the bow thruster. I didn't even try and fuse that, but the thruster switch is nearby. The sanitation system feed is not fused at the battery as it's supposed to be in accordance with ABYC standards, but the fuse block for it is close enough by that there's not much of a cable run for there to be a problem in.

By the way, I'm an amateur. I had to learn this stuff because there's nobody near me - but me! There are far more qualified people on here to give you feedback, but we have the same boats and are going through the same things.

View attachment 46741

BTW, right where that battery is, is where my Vacuflush VG4 unit was installed, replacing the VG3 that had been on the rear bulkhead behind the starboard engine.

I am able to remove it, and get that space back with the new Raritan toilet!

 

[Jammin']

I had two 8D's installed in the center. I moved one battery outboard of the starboard engine to make some more room in the center. One of my fiberglass battery boxes had a hole worn in it. I glassed it up and used a layer of .060" EPDM rubber under the battery box and one inside the battery box under the battery.

 

[Boatsb]

Ok now the basics

1) The starter lead does not get fused. Just a switch.
2) Maximum 4 (3 for CG) wires per terminal.
3) Size and draw determines which one goes on first.
4) All feeds need to be protected 7 inches from the source. Breakers beat fuses in my book.

Now for the next level.

Wires need to be run in a manner that supports them
Wires should be marked.
Grounds are as important as hot wires.
Size should be based on engine room and under debating formulas.

DIY is often done wrong.

 

[brettportzer]

And hence the confusion, because the very experienced surveyor made the note...

Ok now the basics

1) The starter lead does not get fused. Just a switch.
2) Maximum 4 (3 for CG) wires per terminal.
3) Size and draw determines which one goes on first.
4) All feeds need to be protected 7 inches from the source. Breakers beat fuses in my book.

Now for the next level.

Wires need to be run in a manner that supports them
Wires should be marked.
Grounds are as important as hot wires.
Size should be based on engine room and under debating formulas.

DIY is often done wrong.