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Old 11-28-2007, 12:31 PM   #1
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12 volt marine wiring - can anyone help?


okay, i am about to start on the rewiring process of my boat (14' tri hull open bow) and i was seeking some advice and got lots of conflicting advice from the people on a boating forum.

basiclly, i am going to rewire the entire electrical system (NOT motor wiring or harness)... i am going to run my power and ground from the battery to a 6 gang 15 amp switch panel, that will control bilge pump, nav and anchor lights, mood lights, radio and depthfinder.

from that switch panel, power will run individially to each accessory.

the conflicting advice i am getting is wire size.

some say to use 10awg, because the voltage drop will be 3% on a combined distance (power and ground) of 10 ft. is this true? i need to power a 3 amp draw depth finder, 2 lights @ .5 amps each, 2 led @ .7amp each and a bilge pump 5 amps (used very rarely, and only for short bursts) and i am unsure of the radio's draw because i dont actually have one yet.

from my limited automotive wiring experience, i have wired a few car stereos, NEVER using anything larger than 12awg with NO PROBLEMS, even runs to the trunk to power crossovers, etc.

it is 5 ft from the battery to the switch panel, then 5 feet to the front nav light, 5 feet from the panel to the rear anchoring light, 10 ft to the stereo and a total of 10ft to the mood light led's (the first is 3 ft from panel and second is another 7ft)

what do you guys think?

i would like to use 12awg stranded auto type wire... i am not going to spend the extra $$$ for marine wire, because in a few years it is all getting ripped out anyways.


this boat will NEVER be used in salt water.

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Old 11-28-2007, 02:08 PM   #2
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12 volt marine wiring - can anyone help?


12 awg is going to do all you want, whoever told you to use 10 awg for boat accessories must be in the wire making business. Rather than make all the calculations for you ...... go here... http://nooutage.com/vdrop.htm
and use the voltage drop calculator to help you with the voltage drop. You would like 2% or less for dc but even 3% will be fine. Your going to find that 12 is plenty to power the terminal strip and you probably could do the branch circuits in 14 or 16.

Remember to put only one way distances into the calculator

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Old 11-28-2007, 02:15 PM   #3
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12 volt marine wiring - can anyone help?


I would say that 12 gauge wire from the switch panel to the various lights and equipment is OK. But use 10 gauge from the battery/alternator location to the panel if have between 20 and 30 amps expected load, use 8 gauge if you have between 30 and 45 amps load (three 15 amp breakers with (cigarette lighter?)receptacles on each branch circuit).

You can use 14 gauge wire for 15 amp. circuits, 16 gauge wire for 10 amp circuits.

Heating or overheating of the wires depends on the amperes only, not the volts.

Also, for a given resistance of wires (depends on thickness, length, and material) and a given number of amperes being drawn, the same number of volts, not the same percentage of volts, is dropped regardless of the voltage. Because the distances in your case are small, the voltage drop will be minimal for the loads you suggested and the wire sizes I suggested.

Last edited by AllanJ; 11-28-2007 at 02:27 PM.
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Old 11-28-2007, 03:49 PM   #4
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12 volt marine wiring - can anyone help?


I would agree with Alan about the 10 gauge but I calculated your combined load at 15 amps which would show up on the wire supplying the terminal strip if everything was on at the same time. This was to allow for any reasonable additions to the terminal strip like the radio. 12 awg is good for 20 amps which would be 5 amps above that figure. Your distances are so short you will have less than 2 % drop with the wire I suggested. Plus you said it was all going to be torn out in a few years.
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Old 11-29-2007, 01:39 AM   #5
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12 volt marine wiring - can anyone help?


Quote:
Originally Posted by arichard21 View Post

i would like to use 12awg stranded auto type wire... i am not going to spend the extra $$$ for marine wire, because in a few years it is all getting ripped out anyways.


this boat will NEVER be used in salt water.

there is one diffrence between automovite wire and marine wire is that the marine wire is UV/salt water restest the automotive wire is not UV proof at all.

that mean if not UV[ some case sunlight proof ] protected the wire will get brittle in very short time depending on where the sun will " aim " on the wire

the other thing to run power from battery to switch box you need 10 gauage wire both postive and neg wires because you mention trihull that is pretty good chance you have fiberglass vessel there.

and put a master inline fuse near the battery to prevent any short circuit or hevey overload.

Merci, Marc
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Old 11-29-2007, 06:29 AM   #6
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12 volt marine wiring - can anyone help?


Quote:
Originally Posted by frenchelectrican View Post
there is one diffrence between automovite wire and marine wire is that the marine wire is UV/salt water restest the automotive wire is not UV proof at all.

that mean if not UV[ some case sunlight proof ] protected the wire will get brittle in very short time depending on where the sun will " aim " on the wire

the other thing to run power from battery to switch box you need 10 gauage wire both postive and neg wires because you mention trihull that is pretty good chance you have fiberglass vessel there.

and put a master inline fuse near the battery to prevent any short circuit or hevey overload.

Merci, Marc
marc, i mentioned using auto type because the wire wont be exposed to sunlight, as it will be tucked up in the gunwale, and the boat will NEVER be used in salt water... so i should be okay, right?

a master fuse is in the plans as well.
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Old 11-29-2007, 06:47 AM   #7
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12 volt marine wiring - can anyone help?


As with automobiles, the wiring should be multi strand. By this I mean each wire should have many fine strands of copper. Ideally, greater than 32 strands per wire. This is because of vibration.

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