newb-simple wire question

Hello,

I bought an old 1972 bass boat off ebay that is running well, but I have a couple of wiring questions.

I went to buy a switch and some cable off the internet to wire the lights from the battery to the switch (and hopefully eventually a fish finder).

I was just wondering what size battery cable I should get. I ordered the basic connector package that comes with all different sizes, but I am not sure what size cable to get.

It is just a basic marine battery that I bought at Wal Mart. I would go look at the cables now to see, but I am at college and the boat is at home. I would like to order the stuff now so I can work on it when I get home.

Lastly, any tips for doing this procedure?

Thanks

 

The proper size wire is a function of how far it is from the battery or power supply and how much power the device being hooked up draws. I would recomend looking at

http://www.westmarine.com/webapp/wcs/stores/servlet/westadvisor/10001/-1/10001/MarineWire.htm

which has a copy of the sizeing chart for wire based upon draw and distance. Then I normally go one size up just for safety.

 

Ok great thanks.

Now, if I do not know the current the light will draw (the wiring will only be about 8 feet long), can I just go with 16 to be safe? I guess my question is, can you go wrong by just getting the thickest wire?

The reason I do not know the current of the light is that they are old, and have been on the boat for a long time...

 

If you are talking about running lights I just go to West Marine and get an idea of the wattage of the incandecent bulbs used for running lights. The current draw on the bulbs hasn't really changed much in the last 20 years or so. This may not be exact, but it will give you a rough idea of the right size. As for going to larger wire, you can never really go to big (I am sure someone here will point out 3 inch wire as a tad big), but it is more expensive and adds weight. Other than that there shouldn't be a problem.

The other thing to remember is to the extent possible have as few fittings and splices as possible in a wire ru, since each added one increases the resistance in the system.

 

3 inch copper wire is a tad big. I would start looking at liquid-helium chilling of a superconducting cable if you feel the need to go to that kind of overkill.

There is never any harm in going a size or two larger (ie, lower gauge number) when in doubt. It is, however, more expensive and, if you have a lot of wiring runs, a bit heavier.

 

Wire should have adequate rating to ensure it doesn't overheat, and there should be enough volts after wire losses are taken into account to run the device that it feeds electrical power to.

Voltage loss in a wire = amps x ohms.

16 g is adequate for most applications. An 8ft run of 16g copper wire has about 1/16 ohm resistance including the return wire. Allowing a wire loss of 5% in a 12V circuit, it would be fine up to about 10 amps, which would cover most lighting and electronic needs. 16g copper wire is rated at about 20 amps so you can see that for most low voltage applications the rating is less important than the wire loss. The resistance of wire doubles when the gauge is increased by 3; e.g., for 22g, which often used for speaker wire, the resistance for that same 8 ft run would be doubled twice to 1/4 ohm.

For a motor drawing more amps that might run for a long time such as a bilge pump you will need a thicker gauge. For a starter motor that might draw a few hundred amps but only runs for a few seconds at a time wire gauge can be based on about 20% wire loss.

Always protect wiring fed by a source with very high current capability such as a battery with fuses.

 

the fuse goes at the power source ie the battery end

 

FWIW, ABYC recommends no more than a 3% voltage drop for essential loads such as navigation lights.

Good Luck!

 

Look here. Scroll down to Wiring: http://newboatbuilders.com/pages/elect.html

Then look at this table :http://newboatbuilders.com/pages/elect2.html

 

I'm about as novice as you get and found Blue Sea System's circuit wizard pretty niffty. http://beta.circuitwizard.bluesea

 

Oops, forgot the dotcom. http://beta.circuitwizard.bluesea.com