Wiring clean-up [long message alert]

[Esgbradford]

Hi all. I am doing a project to clean-up/improve the wiring in my Newport 27. Some of this isn't specific to Atomic 4 engines, and some is. I'd be glad to share as much of the project that people are interested in (also installing LED lights, an entertainment center, USB power ports).

Currently, the fuses and switches are panel mounted on starboard side of the companion way, and the wiring resembles spaghetti. I am designing a (hopefully) better, organized solution for the wiring cabinet. I plan on leaving the switches in the same area, but upgrading the switch looks; moving the fuses inside, and changing from glass tubes to blade fuses; and updating the supply and return to batteries.

I have reviewed information in several books on yacht electrical systems, and have viewed several schematics on Moyer Marine's site. Much of it was helpful. I have some questions though. And, I realize that the answer to some of these questions might begin with "It depends upon your implementation..."

Anyway, I have a few questions I'd like to get your input on regarding positive supply cables. As I understand it, there should be a fuse close to the battery before heading to the distribution panel. My boat doesn't have this that I can find... so I bought a couple ANL fuse holders. Can someone please help me with determining the appropriate size fuse to supply the distribution panel?

Is the correct way to do this, to add up all the loads the lead might supply, and then chose the next bigger size fuse? My boat doesn't have watermaker, water heater, electric windlass, refrigerator... pretty basic: interior lights, bilge fan, bilge pump, navigation lights, depth sounder, atomic 4, marine VHF radio, stereo head. I am planning on adding 5x 2.1A USB ports, and a TV (approx 3 A).

On a similar note, I think I remember reading that the positive lead to the starter motor doesn't need to be fused. But I don't remember reading that it shouldn't be fused. What is your take on this? And if a fuse on the starter lead is a good idea, what should the fuse size be for the Atomic 4 starter? 200A?

And likewise, my boat has an outboard as an auxiliary motor which has an electric starter. I was thinking I might hard wire it to the batteries too. The manual doesn't state anything about using a fuse on the supply, but it does state the battery must have 245 CCA, 325 MCA. Is there any way to determine from that what size fuse to put on it? Perhaps I should just use a clamp meter and then start the motor and use the reading from that as a guideline for a fuse?

Sorry this message is so long. Your help is appreciated.

Eric

Eric

[edwardc]

Here's my take on it.

Contrary to popular belief, the fuses aren't there o protect your electronics. They're there to protect the wires! As such, they should be sized to the smallest wire they feed. In a strict sense, everywhere you transition to a smaller wire size (such as at the switch panel) should be accompanied by an appropriate sized fuse.

On mine, with #4 marine wire coming off the house battery bank, I used a 150A ANL fuse when I rewired my supply lines. I also brought all the rat's nest of ground wires off of the engine block and onto a single large ground bus bar, and connected a single #4 wire from the ground bus to the engine, close to the starter.

The starter battery does not have an ANL fuse on the line. I was advised by a marine electrician that fuses on the starter line can cause problems. The starting surges can be quite high, even though the steady-state draw of the starter is only about 60A, and you can randomly pop a fuse.

Haven't redone the rat's nest of branch circuits on the DC panel yet, but plan to use #12 wire for the most part, and 20A breakers for most, unless a smaller size is warranted due to existing smaller wire gauges.

Really like the Blue Seas stuff. Redid my AC panel with it, and plan to make the DC panel match.

[The Garbone]

On our current boat the cables feeding the battery selector switch is not fused and neither is the cable from the selector switch to the 2 switch panels. Not saying that it is right but that is how it is.

On my last boat we had a 20amp breaker on the house bank. I actually liked it as it allowed me to work on the fuse/switch panel without disconnecting the batteries.

Something like these would be good and you could even get one for the start circuit if so inclined.

http://www.defender.com/product.jsp?path=-1|328|2289980|2289983&id=2436718

On our last boat we nursed along the PO's wiring. On our new one after looking behind the panel we decided to do a complete gut job on the DC distribution side. Kept the panels but replaced everything else. Added a common -DC bus bar and distributive + bus bars for lights and DC accessory outlets. Properly fused everything and got rid of a lot of crimps and the ones we kept we use proper heat shrunk connectors. Overall a lot of work and we are still not done but well worth the effort.






Here is a picture of the POs -DC bolt/bus. It is the star formation wrapped in electrical tape floating within 3 inches of the unfused +DC feed to the switch panel.

[roadnsky]

Gary-
I had a similar rat's nest.
Took a weekend and some patience to clean up.
Pics of BEFORE and AFTER...

[joe_db]

FYI my starter draws around 120-130 amps, not 60 amps. Another member on here had a 100 amp fuse on the starter and it was too small.

[Esgbradford]

Okay, so I feel sort of sheepish. LOL. I own three books which deal specifically with boat electricity, "Boatowner's Electrical Handbook", "The 12-volt Bible for Boats", and "Boatowner's Mechanical and Electrical Manual". I had looked in the first two books, and hadn't found much on how to size fuses.

Contrary to popular belief, the fuses aren't there o protect your electronics. They're there to protect the wires! As such, they should be sized to the smallest wire they feed.

Then I opened the third book (this book was by Nigel Calder), to see if it had anything on the topic. Sure enough it did, stating nearly exactly what Edward said. It had a good explanation of why, and illustrations of electrical fires. I suppose I could have answered the question myself had I read the third book first.

Thanks Edward for your input, it was very helpful. So, from what I read in that book, and what you say, I conclude this for choosing my fuse size. First, I add the expected amperage draw of the devices being served by the distribution panel, then I use a conductor-size-%-voltage-drop chart to size the supply wire correctly. Then I use that same chart to find the total ampacity the supply wire would be rated for the length it runs, and that number (or up to 150% of it) would be the size of the fuse. [I'm not sure if i should use 10% drop tables or 3%, so I'll be more conservative].

Putting this into practice... If I estimate the total draw to be 32A @ 12V, and the run from the battery swich to the distribution buss/fuses to be 8 feet, then the minimum guage wire (using 3% drop table) would need to be 8 guage. An 8 guage wire running 10' can carry 40A, so the fuse should be between 40A and 60A.

However, if I chose to use a bigger supply cable, 6 Guage, then it's 10' rating (12V 3% drop) would be 80A. So my fuse would be 80A-120A. Would you agree?

Thanks,

Eric

[Esgbradford]

I had a similar rat's nest.
Took a weekend and some patience to clean up.
Pics of BEFORE and AFTER...

Nice work Jerry.

On our last boat we nursed along the PO's wiring. On our new one after looking behind the panel we decided to do a complete gut job on the DC distribution side. Kept the panels but replaced everything else. Added a common -DC bus bar and distributive + bus bars for lights and DC accessory outlets. Properly fused everything and got rid of a lot of crimps and the ones we kept we use proper heat shrunk connectors. Overall a lot of work and we are still not done but well worth the effort.

Gary, do you have photos available of your wiring clean-up?

Thank you both,

Eric

[The Garbone]

Will be working on the boat this weekend and will try for some photos. As it is I am not finished as I have yet to install navigation and deck lights, electronics, engine circuits, waste pump.

[Scuppers]

Remember the lenght of wire is both directions. If the distance of the load is eight feet from the distribution panel, the electrons are traveling sixteen feet. Plan the tinned braided wire size accordingly.

[joe_db]

Here is before and after:
I found it very useful to have the panel able to swing out on hinges to work on. Note the positive bus bars on the circuit breakers have plastic wire loom on them to keep them from rubbing against the wires when the panel is closed up.

[The Garbone]

Here we go.

New behind the panel, the only neg Dc is for the indicator lights.



And here is my still in progress bus bar setup. Not completely dressed. I also plan on building some wood standofffs an covering it with plexiglass.



Note a spelling error.

[edwardc]

... If I estimate the total draw to be 32A @ 12V, and the run from the battery swich to the distribution buss/fuses to be 8 feet, then the minimum guage wire (using 3% drop table) would need to be 8 guage. An 8 guage wire running 10' can carry 40A, so the fuse should be between 40A and 60A.

However, if I chose to use a bigger supply cable, 6 Guage, then it's 10' rating (12V 3% drop) would be 80A. So my fuse would be 80A-120A. Would you agree?

Thanks,

Eric

Sounds right to me. But I'd consider going up to a bigger bus wire size to allow for future needs. I rarely see a battery bus wire smaller than #4. And be sure to get the marine grade wire. Its expensive but worth it. The tinned wire resists corrosion, and the finer strands and the thinner, more flexible insulation makes the wire more supple and easier to bend and route.