Quote:
Originally Posted by keith
Thanks for the advice guys.
One more question. I am doing my calculations for amp draws and adding them up. I have a total of around 280 max amps. Is it necessary to run ground wire back to the engine to support that max amp at 3% loss? It would be highly unlikely that I run the downriggers, crab pot puller, trim tabs, both bilge pumps, both vhf's transmitting, radar radarring, all while spotlighting at the same time! Jeez, I get a headache just thinking about all that going on!
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You don't have to figure it that way, You will never run all that at one time. Residential and commercial services are not even rated to carry all the load that it feeds at one time.
I usually use 4 awg on smaller boats with minimal electronics with a single outboard and step it up from there depending on what I am trying to run. 1/0 or 2/0 will carry about what ever you may try to run on a smaller powerboat with lots of electronics and devices. I would use 2/0 for you main feed if there is over 25 feet of cable between your batteries and your distribution point. Most of the time the point where you split the circuits apart is close to the batteries so there is not much voltage drop there. But the supply under the console to your motors you may get some drop. I like to oversize the wire some so if I add anything in the future I'm covered. 4/0 is only necessary in extreme cases but that would give you like a 400 amp capacity. For the starting circuit #4 awg will carry most loads and will be fine for just that one circuit to the motors but you may want to use #2 depending on how far the run is. I would start with 1/0 or 2/0 for the main wiring off the batteries and disconnect switch to the main distribution point then you can step it down from there and come off with smaller wire to each device. Make sure you fuse each item separate and correctly size the fuses too.
Here is something that might help, Chart for wire amp capacity and a wire size calculator:
http://www.genuinedealz.com/voltage-drop-calculator
Here is a neat calculator software that may work, (I have not tried it out yet myself):
http://api.viglink.com/api/click?format=go&jsonp=vglnk_14226536444427&key=cc2 d0a2fcbd156974a46448313b0e067&libId=74d8e582-f9f1-43e6-bf1d-55f6bc0794c5&loc=http%3A%2F%2Fwww.thehulltruth.com %2Fboating-forum%2F37966-battery-cable-size.html&v=1&out=http%3A%2F%2Fwww.midcoast.com%2F ~aft%2Fprogram%2Fwiresz20.zip&ref=http%3A%2F%2Fwww .thehulltruth.com%2Fboating-forum%2F37966-battery-cable-size-2.html&title=Battery%20Cable%20Size%20-%20The%20Hull%20Truth%20-%20Boating%20and%20Fishing%20Forum&txt=http%3A%2F% 2Fapi.viglink.com%2Fapi%2Fclick%3Fformat%3Dgo%26am p%3Bjsonp%3Dvglnk_14226536444416%26amp%3Bkey%3Dcc2 d0a2fcbd156974a46448313b0e067%26amp%3BlibId%3D...