DC Wiring

[Orbweaver]

Greetings all,
I'm slowly going through all the systems on my Hunter 26.5, and next up is the electrical. The individual circuits are fuse protected, but there is NOT a fuse at the batteries. I do have a battery combine switch, so I could have dual banks if I wanted. However, I think I'm just going to go with a single bank with 2 batteries. The only electrical I have is the lighting, bilge pump, a stereo and the outboard. I may add a VHF at some point, and I'll most likely add solar this summer, since my slip doesn't include shore power.
So, my questions:
1. What's a good fuse for the battery(s)? I'm looking at maybe this one: MRBF
2. Would a circuit breaker also be acceptable? Better?
3. Do I size the fuse for the total expected load, or for the main wires to/from the distribution panel? The cables from the battery to distribution panel are about twice what I'll actually be using.
4. Outboard wiring: What does the code say for protection of the main wiring to the outboard starter? If fused, then I'll probably use a dual fuse block and have that separate from the house.

Thanks all!

 

[Davidasailor26]

For your expected loads a single bank sounds fine.

1. What's a good fuse for the battery(s)? I'm looking at maybe this one: MRBF

Blue Seas MRBF fuses are spoken of quite well. That should be good.

2. Would a circuit breaker also be acceptable? Better?

Circuit breakers aren’t usually used for the first line of overcurrent protection off a battery. They usually aren’t designed to break the type of current that a battery can provide, and could weld themselves closed instead of opening if there’s a dead short. Circuit breakers farther down the line are ok, but I’d stick to a fuse off the battery.

3. Do I size the fuse for the total expected load, or for the main wires to/from the distribution panel? The cables from the battery to distribution panel are about twice what I'll actually be using.

The fuse is there to protect the wire, so it should be sized according to the smallest wire between the fuse and the next overcurrent protection. DC wires do often have a maximum capacity greater than the load because they need to be sized to minimize voltage drop along the cable. Just be sure the breakers at the panel are also sized appropriately for the wires on the individual circuits.

4. Outboard wiring: What does the code say for protection of the main wiring to the outboard starter? If fused, then I'll probably use a dual fuse block and have that separate from the house.

I’ll defer to others more familiar with outboard wiring for that. From what I remember fuses for starter circuits aren’t strictly required, but there are some options to put them there anyway.

 

[Stu Jackson]

3. Do I size the fuse for the total expected load, or for the main wires to/from the distribution panel? The cables from the battery to distribution panel are about twice what I'll actually be using.

Wire Sizing Tables from West Marine (unfortunately they removed the handy charts! around 2016) Marine Wire Size and Ampacity | West Marine www.bluesea.com also has good material on this and fusing, but it's a PDF download and doesn't link. Here's the link to the page, scroll down for the PDF download of the Fuse & Wire Sizing Tables: Reference - Blue Sea Systems

 

[dlochner]

Well, I would add more to this thread, however, @Davidasailor26 and @Stu Jackson pretty much covered it.

Always fuse near the unregulated power supply (battery) and always fuse for the wire size. These are the cardinal rules of DC wiring.

 

[Orbweaver]

Many thanks all! I do have the 3% and 10% charts, so I should be good. I am going to spring for a decent crimp tool and clean up some of the individual circuits. Primarily the bilge pump, because right now it's just connected to one of the Aux switches/fuses in the distribution panel. I'd kinda like to have that connected to the battery upstream of the combine switch.

 

[Orbweaver]

Regarding the need to go through the wiring, I'm just gonna leave these right here:

That radio is going to be replaced with a bluetooth unit that'll be about 1/4 the depth, and that will help the panel fit back into it's original location. I'll be labeling and organizing the wiring, and replacing anything that has questionable splices. I also want to add an auto/manual bilge pump switch, as right now it's just wired to one of the Aux switches. Anyway, now that I have an inventory I'll be ordering up all the bits and bobs I'll need to make this much safer and hopefully more reliable.

 

[LakeOntario270]

Add this Blue Sea battery fuse to your batteries and you will sleep better. I used a 150 amp fuse which is big enough to start my diesel.

https://www.amazon.com/Blue-Sea-Systems-5191-Terminal/dp/B0019ZBTV4/ref=pd_bxgy_img_2/141-8053359-9506564?_encoding=UTF8&pd_rd_i=B0019ZBTV4&pd_rd_r=ff4c84f1-a4b1-435d-8fb3-009e895589bc&pd_rd_w=AM5qa&pd_rd_wg=pkQBW&pf_rd_p=fd3ebcd0-c1a2-44cf-aba2-bbf4810b3732&pf_rd_r=ASFNFXSF2QSKCYJE2QGT&psc=1&refRID=ASFNFXSF2QSKCYJE2QGT

 

[Orbweaver]

Those fuses/terminals are already on the way, although I'm going with 40A for the house and 50A for the outboard.

 

[Ron20324]

AS A "KNOW-NOTHING ABOUT IT".... WILL THE manetism of the speakers have any effect on current flow in the wiring?.

 

[Orbweaver]

yes, but the more important question is how much of an effect? not enough to worry about.

 

[Orbweaver]

I made a LOT of progress today on the wiring. The house and outboard wiring is all fuse protected right at the battery, a mess of cheap butt splicing with no seal is completely replaced, the cabin lights are now wired correct with the center of the socket being POS and the housing negative (ALL the lights were bassackwards, so I think that was a factory feature), and the bilge pump wiring is cleaned up and ready for me to install the new Manual/Auto switch when I get a chance. I also have most of the wiring in place ready for solar install, as well as a battery monitor to keep track of charge and usage.
Other projects included checking and greasing the trailer bearings, adjusting the brakes, finish polishing and wax the topsides, sort out dock lines/fenders and start new foam for the v-berth. It was a busy weekend, and I REALLY want to get finished up so we can haul it to the lake!! This would have been a spectacular weekend on the water. The Admiral had to have pretty extensive surgery last week though, so she rested and I boat projected. At this point everything that's left can be done on the water and I am ready for some play time.

OH, and my fancy new crimp tool and high quality heatshrink connectors have spoiled me for life. I'll never use any of those cheap ones ever again.