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Old 11-06-2020, 21:12   #1
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3 strands of 12 gauge VS 1 of 4

Adding a second battery to boat, trip is coming up in a week, and my A/B switch is mounted in the transom in the back, so I need a second positive wire to run to B on the switch.
I went to Home Depot and they don't seem to have any staff left there, so I was unable to see if they had 25 feet of 4 gauge single wire, but they do sell 25 foot extension cords of 12 gauge wire, so I bought that. it was cheap at $39 bucks. Cut the ends off, and thinking I will strip insulation off all three wires inside and wrap them together, then put a battery terminal on the end.
Is 3 strands of 12 functionally the same as one strand of 4? more or less? Will that extra insulation between the wires cause a problem somehow?
I was thinking even a single strand of 12 would be enough, since it is a 12v system, but I may as well use all three.
Thoughts? crazy?
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Old 11-06-2020, 21:28   #2
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Re: 3 strands of 12 gauge VS 1 of 4

Quote:
Originally Posted by BugzyCan View Post
Adding a second battery to boat, trip is coming up in a week, and my A/B switch is mounted in the transom in the back, so I need a second positive wire to run to B on the switch.
I went to Home Depot and they don't seem to have any staff left there, so I was unable to see if they had 25 feet of 4 gauge single wire, but they do sell 25 foot extension cords of 12 gauge wire, so I bought that. it was cheap at $39 bucks. Cut the ends off, and thinking I will strip insulation off all three wires inside and wrap them together, then put a battery terminal on the end.
Is 3 strands of 12 functionally the same as one strand of 4? more or less? Will that extra insulation between the wires cause a problem somehow?
I was thinking even a single strand of 12 would be enough, since it is a 12v system, but I may as well use all three.
Thoughts? crazy?
It's the amps that count not the volts. Have you considered welding wire as used to connect the workpiece to the welder, high current capability and often available from tool and industrial suppliers. Not tinned but will work if the ideal is not available.
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Old 11-06-2020, 22:56   #3
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Re: 3 strands of 12 gauge VS 1 of 4

Crazy? You asked the question, so please do not be offended. IMHO, yes.

You need marine grade wire, which is stranded, tinned and has the proper insulation. Three strands of 12 gauge is not functionally the same a 4 gauge. The current carrying capacity is a function of the cross sectional area. 4 gauge is .0328 in^2. 12 gauge is .0051 in^2. Three strands of that would be .0153 in^2, or less than half the cross sectional area of 4 gauge.

Please, please, please use the proper wire, terminals and crimping tools, or hire this out to someone who will. You are literally playing with fire, especially when you consider that the wire from the battery to the selector switch is often unfused.

You mentioned 25' feet of wire. You will also need to look into voltage drop based on the round trip wire length and your largest current draw to determine the required wire size.
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Old 12-06-2020, 05:57   #4
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Re: 3 strands of 12 gauge VS 1 of 4

If this is truly a temp fix and we know how that goes. You could get a jumper cable.
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Old 12-06-2020, 11:31   #5
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Re: 3 strands of 12 gauge VS 1 of 4

Bugsy:

Why would you go to HomeDepot when Lordco is just down the street, not to mention Martin Marine in NV?

Draw us a little sketch of just what it is you want to achieve and we'll help you out with the proper dimensions, specs and supplier's names.

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Old 12-06-2020, 11:41   #6
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Re: 3 strands of 12 gauge VS 1 of 4

Tinned wire is definitely better but boats have sailed for years without it. It wasn't an ABYC wiring standard till recently. Since this is a temporary fix, yeah right!!, wouldn't sweat that. Have no idea if it would work but seems like it would. Would get crimp on heat shrink terminals in battery/switch sizes for each wire and install them together. If you only have a fat battery post you can buy battery clamps that have a 1/4"-5/16" threaded post to fit smaller diameter terminals.

Might hit your local marine store/boat yard to find the cable. Genuine Dealz is out of many wire sizes because of manufacturing shut downs with Covid and not expecting shipments for a couple of weeks. That seems to be the case in a lot of places. Genuine Dealz normally would be my go to source for battery cables. I needed a 12" 1 gauge cable and found the wire at my local boat yard and they crimped on the terminals. They were also out of other size cables with no idea of resupply.
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Old 12-06-2020, 12:55   #7
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Re: 3 strands of 12 gauge VS 1 of 4

If you can’t find wire in Vancouver stores and don’t have proper crimping tools I bet pacific yacht systems would cut it and put the ends on for you if you called. You’d need the cable lengh and terminal ring size. (Some batteries are 3/8 and some are 5/16. )

Pay more then online but you could probably pick up same day.
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Old 12-06-2020, 13:27   #8
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Re: 3 strands of 12 gauge VS 1 of 4

How are you going provide circuit protection (fusing)?
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Old 12-06-2020, 13:38   #9
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Re: 3 strands of 12 gauge VS 1 of 4

Below is a link to calculate how many wires to establish equivalent gauge and amp capacity. You need 6 12 gauge to carry the same amps as 4 gauge.

https://www.wirebarn.com/Combined-Wi...tor_ep_42.html
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Old 12-06-2020, 13:52   #10
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Re: 3 strands of 12 gauge VS 1 of 4

I have ordered from bestboatwire.com and received fast service all made up properly to my specs.
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Old 12-06-2020, 16:24   #11
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Re: 3 strands of 12 gauge VS 1 of 4

Oh wow, great information all thanks. I might see if Lordco here has wire by the foot. They may also have the battery terminals since I could not find them at Canadian Tire.
Ok Ok, I will switch out my cable again. Not a big deal since I haven't put ends on anything yet or moved the battery into position.

This is what I am thinking for the wiring. The switch is at back of boat, so the wiring from battery is fairly long. There is no fuse in here anywhere.

Is there any danger having motor charging and solar panel charging at the same time?


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Old 12-06-2020, 17:38   #12
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Re: 3 strands of 12 gauge VS 1 of 4

you ask if there might be problem with the motor and solar charging.


are you using a solar charge controller? might help


consider the solar panel might put out 20 + volts..


what happens when this is fed into the motor charge circuit..hum.. might
not be good. bad?? I wouldn't want 20+ volt back into my alternator.. a couple of diodes would help solve the problem


also in you setup the solar only charges one battery the same as the motor..
at night the solar, without diodes, will draw power from the battery...
not much but its still there.


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Old 12-06-2020, 17:55   #13
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Re: 3 strands of 12 gauge VS 1 of 4

Auto parts store might have what you need in the form of a amplifier installation kit or an inverter installation kit. No matter how you do it, right or wrong, it is still a good idea to put some kind of fuse or breaker near the battery.
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Old 12-06-2020, 18:09   #14
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Re: 3 strands of 12 gauge VS 1 of 4

Now that I think about it, the solar panel does have a fuse inline, not sure about a diode though, do they make diodes that wire into a 4 awg wire to a battery? The cable to the motor has nothing though, pretty sure about that, unless that is built-in by default?

At night I will try to remember to switch the A/B switch to Off to prevent any backflow to solar panel or motor from battery(s).
Solar panel does have a controller.
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Old 13-06-2020, 04:01   #15
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Re: 3 strands of 12 gauge VS 1 of 4

Yikes!!!

This thread is a perfect example of why electrical fires on boats are tragically too common.

Extension cords from Home Depot?? Unfocused questions about solar?? Not a clue about fuses??

The problem here is way too many folks who think that since 12v won't give you a shock if you touch the positive terminal of a battery, no worries mate.The very real danger is a 12v battery has a large amount of energy stored inside. If you don't believe me, take your Mickey Mouse 12ga extension cord setup, put on a welders apron, gauntlets, and face shield. Next short it across the terminals and watch it get red hot, catch the insulation on fire and melt down in big blue flash.

The above is a very bad idea. Much better would be to find someone who is qualified to give you advice and is able to take a look at your setup in person, instead of asking (no insult intended) ignorant questions on an open forum.
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