4th of July boat wiring. Hey gurus !!!

[Midway Tommy]

Don't know why they do it other than cost savings but I've come across a lot of aluminum boats where the manufacturer or dealers used the boat as the ground rather than running separate ground wires for each item. I know it's standard procedure in automobiles but boats are in a totally different environment. It's a no-no in my mind so I always redo the ground wiring right away if I find it's been done that way. 🥴

[Keta]

Stupidity and/or greed.  In saltwater this can cause galvanic corrosion.

I like to put 2 ground busses in, one in back and one in font of the boat connected with 10ga tinned marine wire.  12ga would work for most boat loads but I prefer 10ga.

[jtwill98]

If you're pulling 37 amps through a 22ga wire that works out to 0.323 ohms then you're dropping 12v across the wire. If you only have 12v to feed it and there's a device of some sort, which is functionally in series with the wire, you can never pull that much power unless the device becomes a dead short.

You are correct that this is a dead short -- however long it takes for the wire to heat up and burn through, it will be carrying the max 37 amps. 

You are also correct on the safety standards. 

Wire Size    Suggested Safety Current rating @12v
24 gauge    5.1 amps
22 gauge    6.3 amps
20 gauge    8.9 amps
18 gauge    11.4 amps
16 gauge    13.9 amps
14 gauge    17.7 amps
12 gauge    24.0 amps
10 gauge    32.9 amps

However, for a controlled test scenario, I would have no issue using 22 gauge wire with a 10 or 15 amp fuse inline.  If the device draws more than that, then either the inline fuse or the device fuse will blow. Yes, the wire will heat but for a few seconds test, it will be fine.

Would I wire a boat with that gauge wire? Absolutely not. I would probably look at 10, 12 or 14 gauge wire depending on my futures needs. 

Please note the numbers posted are for automotive safety.  I just checked and the marine numbers are considerably different.  One should check one of the sites online:  https://www.boatus.com/expert-advice/expert-advice-archive/2020/february/choose-the-correct-wire-size   

[boon]

Don't know why they do it other than cost savings but I've come across a lot of aluminum boats where the manufacturer or dealers used the boat as the ground rather than running separate ground wires for each item. I know it's standard procedure in automobiles but boats are in a totally different environment. It's a no-no in my mind so I always redo the ground wiring right away if I find it's been done that way. 🥴

Just being cheap for sure. For what it's worth the largest source/drain of current on an alloy boat is the outboard, and every single one I've checked has had electrical continuity between the negative/ground and the hull, via the bracket and mounting bolts. But they always have a heavy duty negative wire, usually off the starter or the block, back to the battery, which should mean those and the hull never have a potential difference and therefore no galvanic corrosion.

The problem is when they use the hull as the negative and then there's an imperfect connection somewhere in the mix; suddenly you have a voltage difference across the hull and it will start fizzing like an aspirin in the presence of salt water. I keep an eye on insurance auctions for cheap boats, and with alloy boats I would say it's about third place for cause of boats being written off - first place by far being land-based accidents while being towed, ironically, and second being flipping them on bar crossings.

[Rancanfish]

Just a follow up, the issue was resolved with a re-install of tinned #10 wire from the battery to the fuse box. I also upgraded the bilge pump run to #12 tinned wire. I found a section of the lighting that was wrong in color and sizing so I cut that out and ran new. I had to pull my switches down to work on them while scrunched under the dash. I didn't realize I could get that sore working on wires for a few hours.

I added roughly an hour of unnecessary work disconnecting and removing my lighting fixtures. I turned the lights on and after about 10 seconds they went out. In my tired state I 'assumed' a short. After I checked everything I realized I had temporarily put a 1 amp fuse in the lighting circuit. Duh! Put the right fuse in and now both the lights and my new Garmin circuit work as intended.

[Keta]

:0)

[jtwill98]

Just a follow up, the issue was resolved with a re-install of tinned #10 wire from the battery to the fuse box. I also upgraded the bilge pump run to #12 tinned wire.

Nice to hear!

[Dominick]

Does tinned wire mean that solder is put on about 1 inch of wire after the wire is stripped of insulation?  Dominick

[Keta]

No, that is "tinning" the wire.  Tinned wire has every strand coated.

[Dominick]

Does the tinned wire have insulation?  Now I am assuming that it is copper wire coated in tin and is insulated with a rubber or plastic sleeve.  Dominick

[Keta]

Yes.

[Gobi King]

Does the tinned wire have insulation?  Now I am assuming that it is copper wire coated in tin and is insulated with a rubber or plastic sleeve.  Dominick

Dominik
Each copper strand is tinned and then jacketed like a regular insulated  wire .